Patent Publication Number: US-2023148098-A1

Title: Methods and devices for transferring data using sound signals

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 16/150,060, filed Oct. 2, 2018, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure is related to consumer goods and, more particularly, to methods, systems, products, features, services, and other elements directed to media playback or some aspect thereof. 
     BACKGROUND 
     Options for accessing and listening to digital audio in an out-loud setting were limited until in 2002, when SONOS, Inc. began development of a new type of playback system. Sonos then filed one of its first patent applications in 2003, entitled “Method for Synchronizing Audio Playback between Multiple Networked Devices,” and began offering its first media playback systems for sale in 2005. The Sonos Wireless Home Sound System enables people to experience music from many sources via one or more networked playback devices. Through a software control application installed on a controller (e.g., smartphone, tablet, computer, voice input device), one can play what she wants in any room having a networked playback device. Media content (e.g., songs, podcasts, video sound) can be streamed to playback devices such that each room with a playback device can play back corresponding different media content. In addition, rooms can be grouped together for synchronous playback of the same media content, and/or the same media content can be heard in all rooms synchronously. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, aspects, and advantages of the presently disclosed technology may be better understood with regard to the following description, appended claims, and accompanying drawings, as listed below. A person skilled in the relevant art will understand that the features shown in the drawings are for purposes of illustrations, and variations, including different and/or additional features and arrangements thereof, are possible. 
         FIG.  1 A  is a partial cutaway view of an environment having a media playback system configured in accordance with aspects of the disclosed technology. 
         FIG.  1 B  is a schematic diagram of the media playback system of  FIG.  1 A  and one or more networks. 
         FIG.  1 C  is a block diagram of a playback device. 
         FIG.  1 D  is a block diagram of a playback device. 
         FIG.  1 E  is a block diagram of a network microphone device. 
         FIG.  1 F  is a block diagram of a network microphone device. 
         FIG.  1 G  is a block diagram of a playback device. 
         FIG.  1 H  is a partially schematic diagram of a control device. 
         FIGS.  1   -I through  1 L are schematic diagrams of corresponding media playback system zones. 
         FIG.  1 M  is a schematic diagram of media playback system areas. 
         FIG.  2 A  is a front isometric view of a playback device configured in accordance with aspects of the disclosed technology. 
         FIG.  2 B  is a front isometric view of the playback device of  FIG.  3 A  without a grille. 
         FIG.  2 C  is an exploded view of the playback device of  FIG.  2 A . 
         FIG.  3 A  is a front view of a network microphone device configured in accordance with aspects of the disclosed technology. 
         FIG.  3 B  is a side isometric view of the network microphone device of  FIG.  3 A . 
         FIG.  3 C  is an exploded view of the network microphone device of  FIGS.  3 A and  3 B . 
         FIG.  3 D  is an enlarged view of a portion of  FIG.  3 B . 
         FIG.  3 E  is a block diagram of the network microphone device of  FIGS.  3 A- 3 D   
         FIG.  3 F  is a schematic diagram of an example voice input. 
         FIG.  4    is a schematic diagram of an environment in which a playback device is arranged to transmit data using sound signals. 
         FIG.  5    is a flow chart of a method of transmitting data using sound signals. 
         FIG.  6    is a constellation diagram of an example 16-QAM modulation scheme. 
         FIG.  7    is a flow chart of a method of receiving data using sound signals. 
         FIG.  8    shows a waveform of an example received sound transmitted using the method of  FIG.  5   . 
         FIG.  9    shows the in-phase and quadrature components of a demodulated sound signal waveform from  FIG.  8   . 
         FIG.  10    is a schematic diagram of data transfer between playback devices during a setup process. 
     
    
    
     The drawings are for the purpose of illustrating example embodiments, but those of ordinary skill in the art will understand that the technology disclosed herein is not limited to the arrangements and/or instrumentality shown in the drawings. 
     DETAILED DESCRIPTION 
     I. Overview 
     Embodiments described herein relate to the transmission of data using sound signals and to improving the reliability and/or robustness with which such data can be transmitted. This may be beneficial when data is transmitted by sound signals using hardware which is designed to transmit audio signals as its primary purpose. 
     In some embodiments, for example, a method includes encoding a block of data into a plurality of symbols to be transmitted, modulating the symbols onto a sonic carrier signal, and transmitting the modulated data. Transmitting the modulated data involves transmitting a portion the modulated data for a first duration, pausing transmission for a second duration, and repeating the transmitting and pausing with further portions of the modulated data. 
     By including a pause in the transmission, transmission of data using an audio transducer may be made more reliable or robust. It has been found that audio transducers may overheat or otherwise not perform optimally when used for data transmission rather than audio transmission. The pause in transmission reduces this effect and can improve the quality of the transmitted data. 
     In some embodiments, a method includes receiving sound by a microphone, the received sound comprising a block of data modulated on an intermittent sonic carrier signal. The method includes sampling the received signal to generate a sampled data stream, and demodulating the sampled data stream. Demodulating the sampled data stream involves demodulating a portion of the sampled data stream corresponding to a first duration in which the intermittent sonic carrier signal is present, disregarding a portion of the sampled data stream corresponding to a second duration in which the intermittent sonic carrier signal is not present, and repeating the steps of demodulating and disregarding to demodulate further portions of the sampled data stream. 
     In some embodiments, a method of transferring data between a transmitting device and a receiving device includes the transmitting device encoding a block of data into a plurality of symbols to be transmitted, modulating the symbols onto a sonic carrier signal, and transmitting the modulated data. Transmitting the modulated data involves transmitting a portion the modulated data for a first duration, pausing transmission for a second duration, and repeating the transmitting and pausing with further portions of the modulated data. The method further includes a receiving device receiving the transmitted data using a microphone to generate a received signal, sampling the received signal to generate a sampled data stream, and demodulating the sampled data stream. Demodulating the sampled data stream involves demodulating a portion of the sampled data stream corresponding to the first duration, disregarding a portion of the sampled data stream corresponding to the second duration, and repeating the steps of demodulating and disregarding to demodulate further portions of the sampled data stream. 
     In some embodiments, a playback device includes an electroacoustic transducer for generating audio signals, non-transitory storage comprising program code, and a processing system. The program code, when executed by the processing system, causes the playback device to encode a block of data to be transmitted into a plurality of symbols to be transmitted, modulate the symbols onto a sonic carrier signal to generate modulated data, and transmit the modulated data using the electroacoustic transducer. Transmitting the modulated data involves transmitting a portion of the modulated data for a first duration, pausing transmission for second duration, and repeating the transmitting and pausing with further portions of modulated data. 
     In some embodiments, a device includes a microphone configured to receive sound signals, non-transitory storage comprising program code, and a processing system. The program code, when executed by the processing system, causes the device to sample sound received by the microphone to generate a sampled data stream including a block of data modulated on an intermittent sonic carrier signal. The program code then causes the device to demodulate the sampled data stream by demodulating a portion of the sampled data stream corresponding to a first duration in which the intermittent sonic carrier signal is present, disregard a portion of the sampled data stream corresponding to a second duration in which the intermittent sonic carrier signal is not present, and repeat the steps of demodulating and discarding to demodulate further portions of the sampled data stream. 
     In some embodiments, a system includes one or more playback devices and a receiving device. Each of the one or more playback devices includes an electroacoustic transducer for generating audio signals, non-transitory storage comprising program code, and a processing system. The program code, when executed by the processing system, causes the playback device to encode a block of data to be transmitted into a plurality of symbols to be transmitted, modulate the symbols onto a sonic carrier signal to generate modulated data, and transmit the modulated data using the electroacoustic transducer. Transmitting the modulated data involves transmitting a portion of the modulated data for a first duration, pausing transmission for second duration, and repeating the transmitting and pausing with further portions of modulated data. The receiving device includes a microphone configured to receive sound signals, non-transitory storage comprising program code, and a processing system. The program code, when executed by the processing system, causes the receiving device to receive the data transmitted by the one or more playback devices using a microphone to generate a received signal, sample the received signal to generate a sampled data stream, and demodulate the sampled data stream. Demodulating the sampled data stream involves demodulating a portion of the sampled data stream corresponding to the first duration, disregarding a portion of the sampled data stream corresponding to the second duration, and repeating the steps of demodulating and disregarding to demodulate further portions of the sampled data stream. 
     While some examples described herein may refer to functions performed by given actors such as “users,” “listeners,” and/or other entities, it should be understood that this is for purposes of explanation only. The claims should not be interpreted to require action by any such example actor unless explicitly required by the language of the claims themselves. 
     In the Figures, identical reference numbers identify generally similar, and/or identical, elements. To facilitate the discussion of any particular element, the most significant digit or digits of a reference number refers to the Figure in which that element is first introduced. For example, element  110   a  is first introduced and discussed with reference to  FIG.  1 A . Many of the details, dimensions, angles and other features shown in the Figures are merely illustrative of particular embodiments of the disclosed technology. Accordingly, other embodiments can have other details, dimensions, angles and features without departing from the spirit or scope of the disclosure. In addition, those of ordinary skill in the art will appreciate that further embodiments of the various disclosed technologies can be practiced without several of the details described below. 
     II. Suitable Operating Environment 
       FIG.  1 A  is a partial cutaway view of a media playback system  100  distributed in an environment  101  (e.g., a house). The media playback system  100  comprises one or more playback devices  110  (identified individually as playback devices  110   a - n ), one or more network microphone devices (“NMDs”),  120  (identified individually as NMDs  120   a - c ), and one or more control devices  130  (identified individually as control devices  130   a  and  130   b ). 
     As used herein the term “playback device” can generally refer to a network device configured to receive, process, and output data of a media playback system. For example, a playback device can be a network device that receives and processes audio content. In some embodiments, a playback device includes one or more transducers or speakers powered by one or more amplifiers. In other embodiments, however, a playback device includes one of (or neither of) the speaker and the amplifier. For instance, a playback device can comprise one or more amplifiers configured to drive one or more speakers external to the playback device via a corresponding wire or cable. 
     Moreover, as used herein the term NMD (i.e., a “network microphone device”) can generally refer to a network device that is configured for audio detection. In some embodiments, an NMD is a stand-alone device configured primarily for audio detection. In other embodiments, an NMD is incorporated into a playback device (or vice versa). 
     The term “control device” can generally refer to a network device configured to perform functions relevant to facilitating user access, control, and/or configuration of the media playback system  100 . 
     Each of the playback devices  110  is configured to receive audio signals or data from one or more media sources (e.g., one or more remote servers, one or more local devices) and play back the received audio signals or data as sound. The one or more NMDs  120  are configured to receive spoken word commands, and the one or more control devices  130  are configured to receive user input. In response to the received spoken word commands and/or user input, the media playback system  100  can play back audio via one or more of the playback devices  110 . In certain embodiments, the playback devices  110  are configured to commence playback of media content in response to a trigger. For instance, one or more of the playback devices  110  can be configured to play back a morning playlist upon detection of an associated trigger condition (e.g., presence of a user in a kitchen, detection of a coffee machine operation). In some embodiments, for example, the media playback system  100  is configured to play back audio from a first playback device (e.g., the playback device  100   a ) in synchrony with a second playback device (e.g., the playback device  100   b ). Interactions between the playback devices  110 , NMDs  120 , and/or control devices  130  of the media playback system  100  configured in accordance with the various embodiments of the disclosure are described in greater detail below with respect to  FIGS.  1 B- 1 M . 
     In the illustrated embodiment of  FIG.  1 A , the environment  101  comprises a household having several rooms, spaces, and/or playback zones, including (clockwise from upper left) a master bathroom  101   a,  a master bedroom  101   b,  a second bedroom  101   c,  a family room or den  101   d,  an office  101   e,  a living room  101   f,  a dining room  101   g,  a kitchen  101   h,  and an outdoor patio  101   i.  While certain embodiments and examples are described below in the context of a home environment, the technologies described herein may be implemented in other types of environments. In some embodiments, for example, the media playback system  100  can be implemented in one or more commercial settings (e.g., a restaurant, mall, airport, hotel, a retail or other store), one or more vehicles (e.g., a sports utility vehicle, bus, car, a ship, a boat, an airplane), multiple environments (e.g., a combination of home and vehicle environments), and/or another suitable environment where multi-zone audio may be desirable. 
     The media playback system  100  can comprise one or more playback zones, some of which may correspond to the rooms in the environment  101 . The media playback system  100  can be established with one or more playback zones, after which additional zones may be added, or removed to form, for example, the configuration shown in  FIG.  1 A . Each zone may be given a name according to a different room or space such as the office  101   e,  master bathroom  101   a,  master bedroom  101   b,  the second bedroom  101   c,  kitchen  101   h,  dining room  101   g,  living room  101   f,  and/or the balcony  101   i.  In some aspects, a single playback zone may include multiple rooms or spaces. In certain aspects, a single room or space may include multiple playback zones. 
     In the illustrated embodiment of  FIG.  1 A , the master bathroom  101   a,  the second bedroom  101   c,  the office  101   e,  the living room  101   f,  the dining room  101   g,  the kitchen  101   h,  and the outdoor patio  101   i  each include one playback device  110 , and the master bedroom  101   b  and the den  101   d  include a plurality of playback devices  110 . In the master bedroom  101   b,  the playback devices  110   l  and  110   m  may be configured, for example, to play back audio content in synchrony as individual ones of playback devices  110 , as a bonded playback zone, as a consolidated playback device, and/or any combination thereof. Similarly, in the den  101   d,  the playback devices  110   h - j  can be configured, for instance, to play back audio content in synchrony as individual ones of playback devices  110 , as one or more bonded playback devices, and/or as one or more consolidated playback devices. Additional details regarding bonded and consolidated playback devices are described below with respect to  FIGS.  1 B,  1 E, and  1 I- 1 M . 
     In some aspects, one or more of the playback zones in the environment  101  may each be playing different audio content. For instance, a user may be grilling on the patio  101   i  and listening to hip hop music being played by the playback device  110   c  while another user is preparing food in the kitchen  101   h  and listening to classical music played by the playback device  110   b.  In another example, a playback zone may play the same audio content in synchrony with another playback zone. For instance, the user may be in the office  101   e  listening to the playback device  110   f  playing back the same hip hop music being played back by playback device  110   c  on the patio  101   i.  In some aspects, the playback devices  110   c  and  110   f  play back the hip hop music in synchrony such that the user perceives that the audio content is being played seamlessly (or at least substantially seamlessly) while moving between different playback zones. Additional details regarding audio playback synchronization among playback devices and/or zones can be found, for example, in U.S. Pat. No. 8,234,395 entitled, “System and method for synchronizing operations among a plurality of independently clocked digital data processing devices,” which is incorporated herein by reference in its entirety. 
     a. Suitable Media Playback System 
       FIG.  1 B  is a schematic diagram of the media playback system  100  and a cloud network  102 . For ease of illustration, certain devices of the media playback system  100  and the cloud network  102  are omitted from  FIG.  1 B . One or more communication links  103  (referred to hereinafter as “the links  103 ”) communicatively couple the media playback system  100  and the cloud network  102 . 
     The links  103  can comprise, for example, one or more wired networks, one or more wireless networks, one or more wide area networks (WAN), one or more local area networks (LAN), one or more personal area networks (PAN), one or more telecommunication networks (e.g., one or more Global System for Mobiles (GSM) networks, Code Division Multiple Access (CDMA) networks, Long-Term Evolution (LTE) networks, 5G communication network networks, and/or other suitable data transmission protocol networks), etc. The cloud network  102  is configured to deliver media content (e.g., audio content, video content, photographs, social media content) to the media playback system  100  in response to a request transmitted from the media playback system  100  via the links  103 . In some embodiments, the cloud network  102  is further configured to receive data (e.g. voice input data) from the media playback system  100  and correspondingly transmit commands and/or media content to the media playback system  100 . 
     The cloud network  102  comprises computing devices  106  (identified separately as a first computing device  106   a,  a second computing device  106   b,  and a third computing device  106   c ). The computing devices  106  can comprise individual computers or servers, such as, for example, a media streaming service server storing audio and/or other media content, a voice service server, a social media server, a media playback system control server, etc. In some embodiments, one or more of the computing devices  106  comprise modules of a single computer or server. In certain embodiments, one or more of the computing devices  106  comprise one or more modules, computers, and/or servers. Moreover, while the cloud network  102  is described above in the context of a single cloud network, in some embodiments the cloud network  102  comprises a plurality of cloud networks comprising communicatively coupled computing devices. Furthermore, while the cloud network  102  is shown in  FIG.  1 B  as having three of the computing devices  106 , in some embodiments, the cloud network  102  comprises fewer (or more) than three computing devices  106 . 
     The media playback system  100  is configured to receive media content from the networks  102  via the links  103 . The received media content can comprise, for example, a Uniform Resource Identifier (URI) and/or a Uniform Resource Locator (URL). For instance, in some examples, the media playback system  100  can stream, download, or otherwise obtain data from a URI or a URL corresponding to the received media content. A network  104  communicatively couples the links  103  and at least a portion of the devices (e.g., one or more of the playback devices  110 , NMDs  120 , and/or control devices  130 ) of the media playback system  100 . The network  104  can include, for example, a wireless network (e.g., a WiFi network, a Bluetooth, a Z-Wave network, a ZigBee, and/or other suitable wireless communication protocol network) and/or a wired network (e.g., a network comprising Ethernet, Universal Serial Bus (USB), and/or another suitable wired communication). As those of ordinary skill in the art will appreciate, as used herein, “WiFi” can refer to several different communication protocols including, for example, Institute of Electrical and Electronics Engineers (IEEE) 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.11ac, 802.11ad, 802.11af, 802.11ah, 802.11ai, 802.11aj, 802.11aq, 802.11ax,  802 . 1   lay,  802.15, etc. transmitted at 2.4 Gigahertz (GHz), 5 GHz, and/or another suitable frequency. 
     In some embodiments, the network  104  comprises a dedicated communication network that the media playback system  100  uses to transmit messages between individual devices and/or to transmit media content to and from media content sources (e.g., one or more of the computing devices  106 ). In certain embodiments, the network  104  is configured to be accessible only to devices in the media playback system  100 , thereby reducing interference and competition with other household devices. In other embodiments, however, the network  104  comprises an existing household communication network (e.g., a household WiFi network). In some embodiments, the links  103  and the network  104  comprise one or more of the same networks. In some aspects, for example, the links  103  and the network  104  comprise a telecommunication network (e.g., an LTE network, a  5 G network). Moreover, in some embodiments, the media playback system  100  is implemented without the network  104 , and devices comprising the media playback system  100  can communicate with each other, for example, via one or more direct connections, PANs, telecommunication networks, and/or other suitable communication links. 
     In some embodiments, audio content sources may be regularly added or removed from the media playback system  100 . In some embodiments, for example, the media playback system  100  performs an indexing of media items when one or more media content sources are updated, added to, and/or removed from the media playback system  100 . The media playback system  100  can scan identifiable media items in some or all folders and/or directories accessible to the playback devices  110 , and generate or update a media content database comprising metadata (e.g., title, artist, album, track length) and other associated information (e.g., URIs, URLs) for each identifiable media item found. In some embodiments, for example, the media content database is stored on one or more of the playback devices  110 , network microphone devices  120 , and/or control devices  130 . 
     In the illustrated embodiment of  FIG.  1 B , the playback devices  110   l  and  110   m  comprise a group  107   a.  The playback devices  110   l  and  110   m  can be positioned in different rooms in a household and be grouped together in the group  107   a  on a temporary or permanent basis based on user input received at the control device  130   a  and/or another control device  130  in the media playback system  100 . When arranged in the group  107   a,  the playback devices  110   l  and  110   m  can be configured to play back the same or similar audio content in synchrony from one or more audio content sources. In certain embodiments, for example, the group  107   a  comprises a bonded zone in which the playback devices  110   l  and  110   m  comprise left audio and right audio channels, respectively, of multi-channel audio content, thereby producing or enhancing a stereo effect of the audio content. In some embodiments, the group  107   a  includes additional playback devices  110 . In other embodiments, however, the media playback system  100  omits the group  107   a  and/or other grouped arrangements of the playback devices  110 . Additional details regarding groups and other arrangements of playback devices are described in further detail below with respect to  FIGS.  1   -I through IM. 
     The media playback system  100  includes the NMDs  120   a  and  120   b,  each comprising one or more microphones configured to receive voice utterances from a user. In the illustrated embodiment of  FIG.  1 B , the NMD  120   a  is a standalone device and the NMD  120   b  is integrated into the playback device  110   n.  The NMD  120   a,  for example, is configured to receive voice input  121  from a user  123 . In some embodiments, the NMD  120   a  transmits data associated with the received voice input  121  to a voice assistant service (VAS) configured to (i) process the received voice input data and (ii) transmit a corresponding command to the media playback system  100 . In some aspects, for example, the computing device  106   c  comprises one or more modules and/or servers of a VAS (e.g., a VAS operated by one or more of SONOS®, AMAZON®, GOOGLE® APPLE®, MICROSOFT®). The computing device  106   c  can receive the voice input data from the NMD  120   a  via the network  104  and the links  103 . In response to receiving the voice input data, the computing device  106   c  processes the voice input data (i.e., “Play Hey Jude by The Beatles”), and determines that the processed voice input includes a command to play a song (e.g., “Hey Jude”). The computing device  106   c  accordingly transmits commands to the media playback system  100  to play back “Hey Jude” by the Beatles from a suitable media service (e.g., via one or more of the computing devices  106 ) on one or more of the playback devices  110 . 
     b. Suitable Playback Devices 
       FIG.  1 C  is a block diagram of the playback device  110   a  comprising an input/output  111 . The input/output  111  can include an analog I/O  111   a  (e.g., one or more wires, cables, and/or other suitable communication links configured to carry analog signals) and/or a digital I/O  111   b  (e.g., one or more wires, cables, or other suitable communication links configured to carry digital signals). In some embodiments, the analog I/O  111   a  is an audio line-in input connection comprising, for example, an auto-detecting 3.5 mm audio line-in connection. In some embodiments, the digital I/O  111   b  comprises a Sony/Philips Digital Interface Format (S/PDIF) communication interface and/or cable and/or a Toshiba Link (TOSLINK) cable. In some embodiments, the digital I/O  111   b  comprises a High-Definition Multimedia Interface (HDMI) interface and/or cable. In some embodiments, the digital I/O  111   b  includes one or more wireless communication links comprising, for example, a radio frequency (RF), infrared, WiFi, Bluetooth, or another suitable communication protocol. In certain embodiments, the analog I/O  111   a  and the digital  111   b  comprise interfaces (e.g., ports, plugs, jacks) configured to receive connectors of cables transmitting analog and digital signals, respectively, without necessarily including cables. 
     The playback device  110   a,  for example, can receive media content (e.g., audio content comprising music and/or other sounds) from a local audio source  105  via the input/output  111  (e.g., a cable, a wire, a PAN, a Bluetooth connection, an ad hoc wired or wireless communication network, and/or another suitable communication link). The local audio source  105  can comprise, for example, a mobile device (e.g., a smartphone, a tablet, a laptop computer) or another suitable audio component (e.g., a television, a desktop computer, an amplifier, a phonograph, a Blu-ray player, a memory storing digital media files). In some aspects, the local audio source  105  includes local music libraries on a smartphone, a computer, a networked-attached storage (NAS), and/or another suitable device configured to store media files. In certain embodiments, one or more of the playback devices  110 , NMDs  120 , and/or control devices  130  comprise the local audio source  105 . In other embodiments, however, the media playback system omits the local audio source  105  altogether. In some embodiments, the playback device  110   a  does not include an input/output  111  and receives all audio content via the network  104 . 
     The playback device  110   a  further comprises electronics  112 , a user interface  113  (e.g., one or more buttons, knobs, dials, touch-sensitive surfaces, displays, touchscreens), and one or more transducers  114  (referred to hereinafter as “the transducers  114 ”). The electronics  112  is configured to receive audio from an audio source (e.g., the local audio source  105 ) via the input/output  111 , one or more of the computing devices  106   a - c  via the network  104  ( FIG.  1 B )), amplify the received audio, and output the amplified audio for playback via one or more of the transducers  114 . In some embodiments, the playback device  110   a  optionally includes one or more microphones  115  (e.g., a single microphone, a plurality of microphones, a microphone array) (hereinafter referred to as “the microphones  115 ”). In certain embodiments, for example, the playback device  110   a  having one or more of the optional microphones  115  can operate as an NMD configured to receive voice input from a user and correspondingly perform one or more operations based on the received voice input. 
     In the illustrated embodiment of  FIG.  1 C , the electronics  112  comprise one or more processors  112   a  (referred to hereinafter as “the processors  112   a ”), memory  112   b,  software components  112   c,  a network interface  112   d,  one or more audio processing components  112   g  (referred to hereinafter as “the audio components  112   g ”), one or more audio amplifiers  112   h  (referred to hereinafter as “the amplifiers  112   h ”), and power  112   i  (e.g., one or more power supplies, power cables, power receptacles, batteries, induction coils, Power-over Ethernet (POE) interfaces, and/or other suitable sources of electric power). In some embodiments, the electronics  112  optionally include one or more other components  112   j  (e.g., one or more sensors, video displays, touchscreens, battery charging bases). 
     The processors  112   a  can comprise clock-driven computing component(s) configured to process data, and the memory  112   b  can comprise a computer-readable medium (e.g., a tangible, non-transitory computer-readable medium, data storage loaded with one or more of the software components  112   c ) configured to store instructions for performing various operations and/or functions. The processors  112   a  are configured to execute the instructions stored on the memory  112   b  to perform one or more of the operations. The operations can include, for example, causing the playback device  110   a  to retrieve audio data from an audio source (e.g., one or more of the computing devices  106   a - c  ( FIG.  1 B )), and/or another one of the playback devices  110 . In some embodiments, the operations further include causing the playback device  110   a  to send audio data to another one of the playback devices  110   a  and/or another device (e.g., one of the NMDs  120 ). Certain embodiments include operations causing the playback device  110   a  to pair with another of the one or more playback devices  110  to enable a multi-channel audio environment (e.g., a stereo pair, a bonded zone). 
     The processors  112   a  can be further configured to perform operations causing the playback device  110   a  to synchronize playback of audio content with another of the one or more playback devices  110 . As those of ordinary skill in the art will appreciate, during synchronous playback of audio content on a plurality of playback devices, a listener will preferably be unable to perceive time-delay differences between playback of the audio content by the playback device  110   a  and the other one or more other playback devices  110 . Additional details regarding audio playback synchronization among playback devices can be found, for example, in U.S. Pat. No. 8,234,395, which was incorporated by reference above. 
     In some embodiments, the memory  112   b  is further configured to store data associated with the playback device  110   a,  such as one or more zones and/or zone groups of which the playback device  110   a  is a member, audio sources accessible to the playback device  110   a,  and/or a playback queue that the playback device  110   a  (and/or another of the one or more playback devices) can be associated with. The stored data can comprise one or more state variables that are periodically updated and used to describe a state of the playback device  110   a.  The memory  112   b  can also include data associated with a state of one or more of the other devices (e.g., the playback devices  110 , NMDs  120 , control devices  130 ) of the media playback system  100 . In some aspects, for example, the state data is shared during predetermined intervals of time (e.g., every 5 seconds, every 10 seconds, every 60 seconds) among at least a portion of the devices of the media playback system  100 , so that one or more of the devices have the most recent data associated with the media playback system  100 . 
     The network interface  112   d  is configured to facilitate a transmission of data between the playback device  110   a  and one or more other devices on a data network such as, for example, the links  103  and/or the network  104  ( FIG.  1 B ). The network interface  112   d  is configured to transmit and receive data corresponding to media content (e.g., audio content, video content, text, photographs) and other signals (e.g., non-transitory signals) comprising digital packet data including an Internet Protocol (IP)-based source address and/or an IP-based destination address. The network interface  112   d  can parse the digital packet data such that the electronics  112  properly receives and processes the data destined for the playback device  110   a.    
     In the illustrated embodiment of  FIG.  1 C , the network interface  112   d  comprises one or more wireless interfaces  112   e  (referred to hereinafter as “the wireless interface  112   e ”). The wireless interface  112   e  (e.g., a suitable interface comprising one or more antennae) can be configured to wirelessly communicate with one or more other devices (e.g., one or more of the other playback devices  110 , NMDs  120 , and/or control devices  130 ) that are communicatively coupled to the network  104  ( FIG.  1 B ) in accordance with a suitable wireless communication protocol (e.g., WiFi, Bluetooth, LTE). In some embodiments, the network interface  112   d  optionally includes a wired interface  112   f  (e.g., an interface or receptacle configured to receive a network cable such as an Ethernet, a USB-A, USB-C, and/or Thunderbolt cable) configured to communicate over a wired connection with other devices in accordance with a suitable wired communication protocol. In certain embodiments, the network interface  112   d  includes the wired interface  112   f  and excludes the wireless interface  112   e.  In some embodiments, the electronics  112  excludes the network interface  112   d  altogether and transmits and receives media content and/or other data via another communication path (e.g., the input/output  111 ). 
     The audio components  112   g  are configured to process and/or filter data comprising media content received by the electronics  112  (e.g., via the input/output  111  and/or the network interface  112   d ) to produce output audio signals. In some embodiments, the audio processing components  112   g  comprise, for example, one or more digital-to-analog converters (DAC), audio preprocessing components, audio enhancement components, a digital signal processors (DSPs), and/or other suitable audio processing components, modules, circuits, etc. In certain embodiments, one or more of the audio processing components  112   g  can comprise one or more subcomponents of the processors  112   a.  In some embodiments, the electronics  112  omits the audio processing components  112   g.  In some aspects, for example, the processors  112   a  execute instructions stored on the memory  112   b  to perform audio processing operations to produce the output audio signals. 
     The amplifiers  112   h  are configured to receive and amplify the audio output signals produced by the audio processing components  112   g  and/or the processors  112   a.  The amplifiers  112   h  can comprise electronic devices and/or components configured to amplify audio signals to levels sufficient for driving one or more of the transducers  114 . In some embodiments, for example, the amplifiers  112   h  include one or more switching or class-D power amplifiers. In other embodiments, however, the amplifiers include one or more other types of power amplifiers (e.g., linear gain power amplifiers, class-A amplifiers, class-B amplifiers, class-AB amplifiers, class-C amplifiers, class-D amplifiers, class-E amplifiers, class-F amplifiers, class-G and/or class H amplifiers, and/or another suitable type of power amplifier). In certain embodiments, the amplifiers  112   h  comprise a suitable combination of two or more of the foregoing types of power amplifiers. Moreover, in some embodiments, individual ones of the amplifiers  112   h  correspond to individual ones of the transducers  114 . In other embodiments, however, the electronics  112  includes a single one of the amplifiers  112   h  configured to output amplified audio signals to a plurality of the transducers  114 . In some other embodiments, the electronics  112  omits the amplifiers  112   h.    
     The transducers  114  (e.g., one or more speakers and/or speaker drivers) receive the amplified audio signals from the amplifier  112   h  and render or output the amplified audio signals as sound (e.g., audible sound waves having a frequency between about 20 Hertz (Hz) and 20 kilohertz (kHz)). In some embodiments, the transducers  114  can comprise a single transducer. In other embodiments, however, the transducers  114  comprise a plurality of audio transducers. In some embodiments, the transducers  114  comprise more than one type of transducer. For example, the transducers  114  can include one or more low frequency transducers (e.g., subwoofers, woofers), mid-range frequency transducers (e.g., mid-range transducers, mid-woofers), and one or more high frequency transducers (e.g., one or more tweeters). As used herein, “low frequency” can generally refer to audible frequencies below about 500 Hz, “mid-range frequency” can generally refer to audible frequencies between about 500 Hz and about 2 kHz, and “high frequency” can generally refer to audible frequencies above 2 kHz. In certain embodiments, however, one or more of the transducers  114  comprise transducers that do not adhere to the foregoing frequency ranges. For example, one of the transducers  114  may comprise a mid-woofer transducer configured to output sound at frequencies between about 200 Hz and about 5 kHz. 
     By way of illustration, SONOS, Inc. presently offers (or has offered) for sale certain playback devices including, for example, a “SONOS ONE,” “PLAY:1,” “PLAY:3,” “PLAY:5,” “PLAYBAR,” “PLAYBASE,” “CONNECT:AMP,” “CONNECT,” and “SUB.” Other suitable playback devices may additionally or alternatively be used to implement the playback devices of example embodiments disclosed herein. Additionally, one of ordinary skilled in the art will appreciate that a playback device is not limited to the examples described herein or to SONOS product offerings. In some embodiments, for example, one or more playback devices  110  comprises wired or wireless headphones (e.g., over-the-ear headphones, on-ear headphones, in-ear earphones). In other embodiments, one or more of the playback devices  110  comprise a docking station and/or an interface configured to interact with a docking station for personal mobile media playback devices. In certain embodiments, a playback device may be integral to another device or component such as a television, a lighting fixture, or some other device for indoor or outdoor use. In some embodiments, a playback device omits a user interface and/or one or more transducers. For example,  FIG.  1 D  is a block diagram of a playback device  110 p comprising the input/output  111  and electronics  112  without the user interface  113  or transducers  114 . 
       FIG.  1 E  is a block diagram of a bonded playback device  110   q  comprising the playback device  110   a  ( FIG.  1 C ) sonically bonded with the playback device  110   i  (e.g., a subwoofer) ( FIG.  1 A ). In the illustrated embodiment, the playback devices  110   a  and  110   i  are separate ones of the playback devices  110  housed in separate enclosures. In some embodiments, however, the bonded playback device  110   q  comprises a single enclosure housing both the playback devices  110   a  and  110   i.  The bonded playback device  110 q can be configured to process and reproduce sound differently than an unbonded playback device (e.g., the playback device  110   a  of  FIG.  1 C ) and/or paired or bonded playback devices (e.g., the playback devices  110   l  and  110   m  of  FIG.  1 B ). In some embodiments, for example, the playback device  110   a  is full-range playback device configured to render low frequency, mid-range frequency, and high frequency audio content, and the playback device  110   i  is a subwoofer configured to render low frequency audio content. In some aspects, the playback device  110   a,  when bonded with the first playback device, is configured to render only the mid-range and high frequency components of a particular audio content, while the playback device  110   i  renders the low frequency component of the particular audio content. In some embodiments, the bonded playback device  110   q  includes additional playback devices and/or another bonded playback device. Additional playback device embodiments are described in further detail below with respect to  FIGS.  2 A- 3 D . 
     c. Suitable Network Microphone Devices (NMDs) 
       FIG.  1 F  is a block diagram of the NMD  120   a  ( FIGS.  1 A and  1 B ). The NMD  120   a  includes one or more voice processing components  124  (hereinafter “the voice components  124 ”) and several components described with respect to the playback device  110   a  ( FIG.  1 C ) including the processors  112   a,  the memory  112   b,  and the microphones  115 . The NMD  120   a  optionally comprises other components also included in the playback device  110   a  ( FIG.  1 C ), such as the user interface  113  and/or the transducers  114 . In some embodiments, the NMD  120   a  is configured as a media playback device (e.g., one or more of the playback devices  110 ), and further includes, for example, one or more of the audio components  112   g  ( FIG.  1 C ), the amplifiers  114 , and/or other playback device components. In certain embodiments, the NMD  120   a  comprises an Internet of Things (IoT) device such as, for example, a thermostat, alarm panel, fire and/or smoke detector, etc. In some embodiments, the NMD  120   a  comprises the microphones  115 , the voice processing  124 , and only a portion of the components of the electronics  112  described above with respect to  FIG.  1 B . In some aspects, for example, the NMD  120   a  includes the processor  112   a  and the memory  112   b  ( FIG.  1 B ), while omitting one or more other components of the electronics  112 . In some embodiments, the NMD  120   a  includes additional components (e.g., one or more sensors, cameras, thermometers, barometers, hygrometers). 
     In some embodiments, an NMD can be integrated into a playback device.  FIG.  1 G  is a block diagram of a playback device  110   r  comprising an NMD  120   d.  The playback device  110   r  can comprise many or all of the components of the playback device  110   a  and further include the microphones  115  and voice processing  124  ( FIG.  1 F ). The playback device  110   r  optionally includes an integrated control device  130   c.  The control device  130   c  can comprise, for example, a user interface (e.g., the user interface  113  of  FIG.  1 B ) configured to receive user input (e.g., touch input, voice input) without a separate control device. In other embodiments, however, the playback device  110   r  receives commands from another control device (e.g., the control device  130   a  of  FIG.  1 B ). Additional NMD embodiments are described in further detail below with respect to  FIGS.  3 A- 3 F . 
     Referring again to  FIG.  1 F , the microphones  115  are configured to acquire, capture, and/or receive sound from an environment (e.g., the environment  101  of  FIG.  1 A ) and/or a room in which the NMD  120   a  is positioned. The received sound can include, for example, vocal utterances, audio played back by the NMD  120   a  and/or another playback device, background voices, ambient sounds, etc. The microphones  115  convert the received sound into electrical signals to produce microphone data. The voice processing  124  receives and analyzes the microphone data to determine whether a voice input is present in the microphone data. The voice input can comprise, for example, an activation word followed by an utterance including a user request. As those of ordinary skill in the art will appreciate, an activation word is a word or other audio cue that signifying a user voice input. For instance, in querying the AMAZON® VAS, a user might speak the activation word “Alexa.” Other examples include “Ok, Google” for invoking the GOOGLE® VAS and “Hey, Siri” for invoking the APPLE® VAS. 
     After detecting the activation word, voice processing  124  monitors the microphone data for an accompanying user request in the voice input. The user request may include, for example, a command to control a third-party device, such as a thermostat (e.g., NEST® thermostat), an illumination device (e.g., a PHILIPS HUE® lighting device), or a media playback device (e.g., a Sonos® playback device). For example, a user might speak the activation word “Alexa” followed by the utterance “set the thermostat to 68 degrees” to set a temperature in a home (e.g., the environment  101  of  FIG.  1 A ). The user might speak the same activation word followed by the utterance “turn on the living room” to turn on illumination devices in a living room area of the home. The user may similarly speak an activation word followed by a request to play a particular song, an album, or a playlist of music on a playback device in the home. Additional description regarding receiving and processing voice input data can be found in further detail below with respect to  FIGS.  3 A- 3 F . 
     d. Suitable Control Devices 
       FIG.  1 H  is a partially schematic diagram of the control device  130   a  ( FIGS.  1 A and  1 B ). As used herein, the term “control device” can be used interchangeably with “controller” or “control system.” Among other features, the control device  130   a  is configured to receive user input related to the media playback system  100  and, in response, cause one or more devices in the media playback system  100  to perform an action(s) or operation(s) corresponding to the user input. In the illustrated embodiment, the control device  130   a  comprises a smartphone (e.g., an iPhone™, an Android phone) on which media playback system controller application software is installed. In some embodiments, the control device  130   a  comprises, for example, a tablet (e.g., an iPad™), a computer (e.g., a laptop computer, a desktop computer), and/or another suitable device (e.g., a television, an automobile audio head unit, an IoT device). In certain embodiments, the control device  130   a  comprises a dedicated controller for the media playback system  100 . In other embodiments, as described above with respect to  FIG.  1 G , the control device  130   a  is integrated into another device in the media playback system  100  (e.g., one more of the playback devices  110 , NMDs  120 , and/or other suitable devices configured to communicate over a network). 
     The control device  130   a  includes electronics  132 , a user interface  133 , one or more speakers  134 , and one or more microphones  135 . The electronics  132  comprise one or more processors  132   a  (referred to hereinafter as “the processors  132   a ”), a memory  132   b,  software components  132   c,  and a network interface  132   d.  The processor  132   a  can be configured to perform functions relevant to facilitating user access, control, and configuration of the media playback system  100 . The memory  132   b  can comprise data storage that can be loaded with one or more of the software components executable by the processor  302  to perform those functions. The software components  132   c  can comprise applications and/or other executable software configured to facilitate control of the media playback system  100 . The memory  112   b  can be configured to store, for example, the software components  132   c,  media playback system controller application software, and/or other data associated with the media playback system  100  and the user. 
     The network interface  132   d  is configured to facilitate network communications between the control device  130   a  and one or more other devices in the media playback system  100 , and/or one or more remote devices. In some embodiments, the network interface  132  is configured to operate according to one or more suitable communication industry standards (e.g., infrared, radio, wired standards including IEEE 802.3, wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4G, LTE). The network interface  132   d  can be configured, for example, to transmit data to and/or receive data from the playback devices  110 , the NMDs  120 , other ones of the control devices  130 , one of the computing devices  106  of  FIG.  1 B , devices comprising one or more other media playback systems, etc. The transmitted and/or received data can include, for example, playback device control commands, state variables, playback zone and/or zone group configurations. For instance, based on user input received at the user interface  133 , the network interface  132   d  can transmit a playback device control command (e.g., volume control, audio playback control, audio content selection) from the control device  304  to one or more of the playback devices  100 . The network interface  132   d  can also transmit and/or receive configuration changes such as, for example, adding/removing one or more playback devices  100  to/from a zone, adding/removing one or more zones to/from a zone group, forming a bonded or consolidated player, separating one or more playback devices from a bonded or consolidated player, among others. Additional description of zones and groups can be found below with respect to  FIGS.  1   -I through  1 M. 
     The user interface  133  is configured to receive user input and can facilitate control of the media playback system  100 . The user interface  133  includes media content art  133   a  (e.g., album art, lyrics, videos), a playback status indicator  133   b  (e.g., an elapsed and/or remaining time indicator), media content information region  133   c,  a playback control region  133   d,  and a zone indicator  133   e.  The media content information region  133   c  can include a display of relevant information (e.g., title, artist, album, genre, release year) about media content currently playing and/or media content in a queue or playlist. The playback control region  133   d  can include selectable (e.g., via touch input and/or via a cursor or another suitable selector) icons to cause one or more playback devices in a selected playback zone or zone group to perform playback actions such as, for example, play or pause, fast forward, rewind, skip to next, skip to previous, enter/exit shuffle mode, enter/exit repeat mode, enter/exit cross fade mode, etc. The playback control region  133   d  may also include selectable icons to modify equalization settings, playback volume, and/or other suitable playback actions. In the illustrated embodiment, the user interface  133  comprises a display presented on a touch screen interface of a smartphone (e.g., an iPhone™, an Android phone). In some embodiments, however, user interfaces of varying formats, styles, and interactive sequences may alternatively be implemented on one or more network devices to provide comparable control access to a media playback system. 
     The one or more speakers  134  (e.g., one or more transducers) can be configured to output sound to the user of the control device  130   a.  In some embodiments, the one or more speakers comprise individual transducers configured to correspondingly output low frequencies, mid-range frequencies, and/or high frequencies. In some aspects, for example, the control device  130   a  is configured as a playback device (e.g., one of the playback devices  110 ). Similarly, in some embodiments the control device  130   a  is configured as an NMD (e.g., one of the NMDs  120 ), receiving voice commands and other sounds via the one or more microphones  135 . 
     The one or more microphones  135  can comprise, for example, one or more condenser microphones, electret condenser microphones, dynamic microphones, and/or other suitable types of microphones or transducers. In some embodiments, two or more of the microphones  135  are arranged to capture location information of an audio source (e.g., voice, audible sound) and/or configured to facilitate filtering of background noise. Moreover, in certain embodiments, the control device  130   a  is configured to operate as playback device and an NMD. In other embodiments, however, the control device  130   a  omits the one or more speakers  134  and/or the one or more microphones  135 . For instance, the control device  130   a  may comprise a device (e.g., a thermostat, an IoT device, a network device) comprising a portion of the electronics  132  and the user interface  133  (e.g., a touch screen) without any speakers or microphones. 
     e. Suitable Playback Device Configurations 
       FIGS.  1   -I through  1 M show example configurations of playback devices in zones and zone groups. Referring first to  FIG.  1 M , in one example, a single playback device may belong to a zone. For example, the playback device  110   g  in the second bedroom  101   c  ( FIG.  1 A ) may belong to Zone C. In some implementations described below, multiple playback devices may be “bonded” to form a “bonded pair” which together form a single zone. For example, the playback device  110   l  (e.g., a left playback device) can be bonded to the playback device  110   m  (e.g., a right playback device) to form Zone B. Bonded playback devices may have different playback responsibilities (e.g., channel responsibilities). In another implementation described below, multiple playback devices may be merged to form a single zone. For example, the playback device  110   h  (e.g., a front playback device) may be merged with the playback device  110   i  (e.g., a subwoofer), and the playback devices  110   j  and  110   k  (e.g., left and right surround speakers, respectively) to form a single Zone D. In another example, the playback devices  110   g  and  110   h  can be merged to form a merged group or a zone group  108   b.  The merged playback devices  110   g  and  110   h  may not be specifically assigned different playback responsibilities. That is, the merged playback devices  110   h  and  110   i  may, aside from playing audio content in synchrony, each play audio content as they would if they were not merged. 
     Each zone in the media playback system  100  may be provided for control as a single user interface (UI) entity. For example, Zone A may be provided as a single entity named Master Bathroom. Zone B may be provided as a single entity named Master Bedroom. Zone C may be provided as a single entity named Second Bedroom. 
     Playback devices that are bonded may have different playback responsibilities, such as responsibilities for certain audio channels. For example, as shown in  FIG.  1   -I, the playback devices  110   l  and  110   m  may be bonded so as to produce or enhance a stereo effect of audio content. In this example, the playback device  110   l  may be configured to play a left channel audio component, while the playback device  110   k  may be configured to play a right channel audio component. In some implementations, such stereo bonding may be referred to as “pairing.” 
     Additionally, bonded playback devices may have additional and/or different respective speaker drivers. As shown in  FIG.  1 J , the playback device  110   h  named Front may be bonded with the playback device  110   i  named SUB. The Front device  110   h  can be configured to render a range of mid to high frequencies and the SUB device  110   i  can be configured render low frequencies. When unbonded, however, the Front device  110   h  can be configured render a full range of frequencies. As another example,  FIG.  1 K  shows the Front and SUB devices  110   h  and  110   i  further bonded with Left and Right playback devices  110   j  and  110   k,  respectively. In some implementations, the Right and Left devices  110   j  and  102   k  can be configured to form surround or “satellite” channels of a home theater system. The bonded playback devices  110   h,    110   i,    110   j,  and  110   k  may form a single Zone D ( FIG.  1 M ). 
     Playback devices that are merged may not have assigned playback responsibilities, and may each render the full range of audio content the respective playback device is capable of. Nevertheless, merged devices may be represented as a single UI entity (i.e., a zone, as discussed above). For instance, the playback devices  110   a  and  110   n  of the master bathroom have the single UI entity of Zone A. In one embodiment, the playback devices  110   a  and  110   n  may each output the full range of audio content each respective playback devices  110   a  and  110   n  are capable of, in synchrony. 
     In some embodiments, an NMD is bonded or merged with another device so as to form a zone. For example, the NMD  120   b  may be bonded with the playback device  110   e,  which together form Zone F, named Living Room. In other embodiments, a stand-alone network microphone device may be in a zone by itself. In other embodiments, however, a stand-alone network microphone device may not be associated with a zone. Additional details regarding associating network microphone devices and playback devices as designated or default devices may be found, for example, in previously referenced U.S. patent application Ser. No. 15/438,749. 
     Zones of individual, bonded, and/or merged devices may be grouped to form a zone group. For example, referring to  FIG.  1 M , Zone A may be grouped with Zone B to form a zone group  108   a  that includes the two zones. Similarly, Zone G may be grouped with Zone H to form the zone group  108   b.  As another example, Zone A may be grouped with one or more other Zones C-I. The Zones A-I may be grouped and ungrouped in numerous ways. For example, three, four, five, or more (e.g., all) of the Zones A-I may be grouped. When grouped, the zones of individual and/or bonded playback devices may play back audio in synchrony with one another, as described in previously referenced U.S. Pat. No. 8,234,395. Playback devices may be dynamically grouped and ungrouped to form new or different groups that synchronously play back audio content. 
     In various implementations, the zones in an environment may be the default name of a zone within the group or a combination of the names of the zones within a zone group. For example, Zone Group  108   b  can have be assigned a name such as “Dining+Kitchen”, as shown in  FIG.  1 M . In some embodiments, a zone group may be given a unique name selected by a user. 
     Certain data may be stored in a memory of a playback device (e.g., the memory  112   c  of  FIG.  1 C ) as one or more state variables that are periodically updated and used to describe the state of a playback zone, the playback device(s), and/or a zone group associated therewith. The memory may also include the data associated with the state of the other devices of the media system, and shared from time to time among the devices so that one or more of the devices have the most recent data associated with the system. 
     In some embodiments, the memory may store instances of various variable types associated with the states. Variables instances may be stored with identifiers (e.g., tags) corresponding to type. For example, certain identifiers may be a first type “a1” to identify playback device(s) of a zone, a second type “b1” to identify playback device(s) that may be bonded in the zone, and a third type “c1” to identify a zone group to which the zone may belong. As a related example, identifiers associated with the second bedroom  101   c  may indicate that the playback device is the only playback device of the Zone C and not in a zone group. Identifiers associated with the Den may indicate that the Den is not grouped with other zones but includes bonded playback devices  110   h - 110   k.  Identifiers associated with the Dining Room may indicate that the Dining Room is part of the Dining+Kitchen zone group  108   b  and that devices  110   b  and  110   d  are grouped ( FIG.  1 L ). Identifiers associated with the Kitchen may indicate the same or similar information by virtue of the Kitchen being part of the Dining+Kitchen zone group  108   b.  Other example zone variables and identifiers are described below. 
     In yet another example, the media playback system  100  may variables or identifiers representing other associations of zones and zone groups, such as identifiers associated with Areas, as shown in  FIG.  1 M . An area may involve a cluster of zone groups and/or zones not within a zone group. For instance,  FIG.  1 M  shows an Upper Area  109   a  including Zones A-D, and a Lower Area  109   b  including Zones E-I. In one aspect, an Area may be used to invoke a cluster of zone groups and/or zones that share one or more zones and/or zone groups of another cluster. In another aspect, this differs from a zone group, which does not share a zone with another zone group. Further examples of techniques for implementing Areas may be found, for example, in U.S. application Ser. No. 15/682,506 filed Aug. 21, 2017 and titled “Room Association Based on Name,” and U.S. Pat. No. 8,483,853 filed Sep. 11, 2007, and titled “Controlling and manipulating groupings in a multi-zone media system.” Each of these applications is incorporated herein by reference in its entirety. In some embodiments, the media playback system  100  may not implement Areas, in which case the system may not store variables associated with Areas. 
     III. Example Systems and Devices 
       FIG.  2 A  is a front isometric view of a playback device  210  configured in accordance with aspects of the disclosed technology.  FIG.  2 B  is a front isometric view of the playback device  210  without a grille  216   e.    FIG.  2 C  is an exploded view of the playback device  210 . Referring to  FIGS.  2 A- 2 C  together, the playback device  210  comprises a housing  216  that includes an upper portion  216   a,  a right or first side portion  216   b,  a lower portion  216   c,  a left or second side portion  216   d,  the grille  216   e,  and a rear portion  216   f.  A plurality of fasteners  216   g  (e.g., one or more screws, rivets, clips) attaches a frame  216   h  to the housing  216 . A cavity  216   j  ( FIG.  2 C ) in the housing  216  is configured to receive the frame  216   h  and electronics  212 . The frame  216   h  is configured to carry a plurality of transducers  214  (identified individually in  FIG.  2 B  as transducers  214   a - f ). The electronics  212  (e.g., the electronics  112  of  FIG.  1 C ) is configured to receive audio content from an audio source and send electrical signals corresponding to the audio content to the transducers  214  for playback. 
     The transducers  214  are configured to receive the electrical signals from the electronics  112 , and further configured to convert the received electrical signals into audible sound during playback. For instance, the transducers  214   a - c  (e.g., tweeters) can be configured to output high frequency sound (e.g., sound waves having a frequency greater than about 2 kHz). The transducers  214   d - f  (e.g., mid-woofers, woofers, midrange speakers) can be configured output sound at frequencies lower than the transducers  214   a - c  (e.g., sound waves having a frequency lower than about 2 kHz). In some embodiments, the playback device  210  includes a number of transducers different than those illustrated in  FIGS.  2 A- 2 C . For example, as described in further detail below with respect to  FIGS.  3 A- 3 C , the playback device  210  can include fewer than six transducers (e.g., one, two, three). In other embodiments, however, the playback device  210  includes more than six transducers (e.g., nine, ten). Moreover, in some embodiments, all or a portion of the transducers  214  are configured to operate as a phased array to desirably adjust (e.g., narrow or widen) a radiation pattern of the transducers  214 , thereby altering a user&#39;s perception of the sound emitted from the playback device  210 . 
     In the illustrated embodiment of  FIGS.  2 A- 2 C , a filter  216   i  is axially aligned with the transducer  214   b.  The filter  216   i  can be configured to desirably attenuate a predetermined range of frequencies that the transducer  214   b  outputs to improve sound quality and a perceived sound stage output collectively by the transducers  214 . In some embodiments, however, the playback device  210  omits the filter  216   i.  In other embodiments, the playback device  210  includes one or more additional filters aligned with the transducers  214   b  and/or at least another of the transducers  214 . 
       FIGS.  3 A and  3 B  are front and right isometric side views, respectively, of an NMD  320  configured in accordance with embodiments of the disclosed technology.  FIG.  3 C  is an exploded view of the NMD  320 .  FIG.  3 D  is an enlarged view of a portion of  FIG.  3 B  including a user interface  313  of the NMD  320 . Referring first to  FIGS.  3 A- 3 C , the NMD  320  includes a housing  316  comprising an upper portion  316   a,  a lower portion  316   b  and an intermediate portion  316   c  (e.g., a grille). A plurality of ports, holes or apertures  316   d  in the upper portion  316   a  allow sound to pass through to one or more microphones  315  ( FIG.  3 C ) positioned within the housing  316 . The one or more microphones  315  are configured to received sound via the apertures  316   d  and produce electrical signals based on the received sound. In the illustrated embodiment, a frame  316   e  ( FIG.  3 C ) of the housing  316  surrounds cavities  316   f  and  316   g  configured to house, respectively, a first transducer  314   a  (e.g., a tweeter) and a second transducer  314   b  (e.g., a mid-woofer, a midrange speaker, a woofer). In other embodiments, however, the NMD  320  includes a single transducer, or more than two (e.g., two, five, six) transducers. In certain embodiments, the NMD  320  omits the transducers  314   a  and  314   b  altogether. 
     Electronics  312  ( FIG.  3 C ) includes components configured to drive the transducers  314   a  and  314   b,  and further configured to analyze audio data corresponding to the electrical signals produced by the one or more microphones  315 . In some embodiments, for example, the electronics  312  comprises many or all of the components of the electronics  112  described above with respect to  FIG.  1 C . In certain embodiments, the electronics  312  includes components described above with respect to  FIG.  1 F  such as, for example, the one or more processors  112   a,  the memory  112   b,  the software components  112   c,  the network interface  112   d,  etc. In some embodiments, the electronics  312  includes additional suitable components (e.g., proximity or other sensors). 
     Referring to  FIG.  3 D , the user interface  313  includes a plurality of control surfaces (e.g., buttons, knobs, capacitive surfaces) including a first control surface  313   a  (e.g., a previous control), a second control surface  313   b  (e.g., a next control), and a third control surface  313   c  (e.g., a play and/or pause control). A fourth control surface  313   d  is configured to receive touch input corresponding to activation and deactivation of the one or microphones  315 . A first indicator  313   e  (e.g., one or more light emitting diodes (LEDs) or another suitable illuminator) can be configured to illuminate only when the one or more microphones  315  are activated. A second indicator  313   f  (e.g., one or more LEDs) can be configured to remain solid during normal operation and to blink or otherwise change from solid to indicate a detection of voice activity. In some embodiments, the user interface  313  includes additional or fewer control surfaces and illuminators. In one embodiment, for example, the user interface  313  includes the first indicator  313   e,  omitting the second indicator  313   f.  Moreover, in certain embodiments, the NMD  320  comprises a playback device and a control device, and the user interface  313  comprises the user interface of the control device. 
     Referring to  FIGS.  3 A- 3 D  together, the NMD  320  is configured to receive voice commands from one or more adjacent users via the one or more microphones  315 . As described above with respect to  FIG.  1 B , the one or more microphones  315  can acquire, capture, or record sound in a vicinity (e.g., a region within  10   m  or less of the NMD  320 ) and transmit electrical signals corresponding to the recorded sound to the electronics  312 . The electronics  312  can process the electrical signals and can analyze the resulting audio data to determine a presence of one or more voice commands (e.g., one or more activation words). In some embodiments, for example, after detection of one or more suitable voice commands, the NMD  320  is configured to transmit a portion of the recorded audio data to another device and/or a remote server (e.g., one or more of the computing devices  106  of  FIG.  1 B ) for further analysis. The remote server can analyze the audio data, determine an appropriate action based on the voice command, and transmit a message to the NMD  320  to perform the appropriate action. For instance, a user may speak “Sonos, play Michael Jackson.” The NMD  320  can, via the one or more microphones  315 , record the user&#39;s voice utterance, determine the presence of a voice command, and transmit the audio data having the voice command to a remote server (e.g., one or more of the remote computing devices  106  of  FIG.  1 B , one or more servers of a VAS and/or another suitable service). The remote server can analyze the audio data and determine an action corresponding to the command. The remote server can then transmit a command to the NMD  320  to perform the determined action (e.g., play back audio content related to Michael Jackson). The NMD  320  can receive the command and play back the audio content related to Michael Jackson from a media content source. As described above with respect to  FIG.  1 B , suitable content sources can include a device or storage communicatively coupled to the NMD  320  via a LAN (e.g., the network  104  of  FIG.  1 B ), a remote server (e.g., one or more of the remote computing devices  106  of  FIG.  1 B ), etc. In certain embodiments, however, the NMD  320  determines and/or performs one or more actions corresponding to the one or more voice commands without intervention or involvement of an external device, computer, or server. 
       FIG.  3 E  is a functional block diagram showing additional features of the NMD  320  in accordance with aspects of the disclosure. The NMD  320  includes components configured to facilitate voice command capture including voice activity detector component(s)  312   k,  beam former components  312   l,  acoustic echo cancellation (AEC) and/or self-sound suppression components  312   m,  activation word detector components  312   n,  and voice/speech conversion components  312   o  (e.g., voice-to-text and text-to-voice). In the illustrated embodiment of  FIG.  3 E , the foregoing components  312   k - 312   o  are shown as separate components. In some embodiments, however, one or more of the components  312   k - 312   o  are subcomponents of the processors  112   a.    
     The beamforming and self-sound suppression components  312   l  and  312   m  are configured to detect an audio signal and determine aspects of voice input represented in the detected audio signal, such as the direction, amplitude, frequency spectrum, etc. The voice activity detector activity components  312   k  are operably coupled with the beamforming and AEC components  312   l  and  312   m  and are configured to determine a direction and/or directions from which voice activity is likely to have occurred in the detected audio signal. Potential speech directions can be identified by monitoring metrics which distinguish speech from other sounds. Such metrics can include, for example, energy within the speech band relative to background noise and entropy within the speech band, which is measure of spectral structure. As those of ordinary skill in the art will appreciate, speech typically has a lower entropy than most common background noise. 
     The activation word detector components  312   n  are configured to monitor and analyze received audio to determine if any activation words (e.g., wake words) are present in the received audio. The activation word detector components  312   n  may analyze the received audio using an activation word detection algorithm. If the activation word detector  312   n  detects an activation word, the NMD  320  may process voice input contained in the received audio. Example activation word detection algorithms accept audio as input and provide an indication of whether an activation word is present in the audio. Many first- and third-party activation word detection algorithms are known and commercially available. For instance, operators of a voice service may make their algorithm available for use in third-party devices. Alternatively, an algorithm may be trained to detect certain activation words. In some embodiments, the activation word detector  312   n  runs multiple activation word detection algorithms on the received audio simultaneously (or substantially simultaneously). As noted above, different voice services (e.g. AMAZON&#39;s ALEXA®, APPLE&#39;s SIRI®, or MICROSOFT&#39;s CORTANA®) can each use a different activation word for invoking their respective voice service. To support multiple services, the activation word detector  312   n  may run the received audio through the activation word detection algorithm for each supported voice service in parallel. 
     The speech/text conversion components  312   o  may facilitate processing by converting speech in the voice input to text. In some embodiments, the electronics  312  can include voice recognition software that is trained to a particular user or a particular set of users associated with a household. Such voice recognition software may implement voice-processing algorithms that are tuned to specific voice profile(s). Tuning to specific voice profiles may require less computationally intensive algorithms than traditional voice activity services, which typically sample from a broad base of users and diverse requests that are not targeted to media playback systems. 
       FIG.  3 F  is a schematic diagram of an example voice input  328  captured by the NMD  320  in accordance with aspects of the disclosure. The voice input  328  can include an activation word portion  328   a  and a voice utterance portion  328   b.  In some embodiments, the activation word  557   a  can be a known activation word, such as “Alexa,” which is associated with AMAZON&#39;s ALEXA®. In other embodiments, however, the voice input  328  may not include an activation word. In some embodiments, a network microphone device may output an audible and/or visible response upon detection of the activation word portion  328   a.  In addition or alternately, an NMB may output an audible and/or visible response after processing a voice input and/or a series of voice inputs. 
     The voice utterance portion  328   b  may include, for example, one or more spoken commands (identified individually as a first command  328   c  and a second command  328   e ) and one or more spoken keywords (identified individually as a first keyword  328   d  and a second keyword  328   f ). In one example, the first command  328   c  can be a command to play music, such as a specific song, album, playlist, etc. In this example, the keywords may be one or words identifying one or more zones in which the music is to be played, such as the Living Room and the Dining Room shown in  FIG.  1 A . In some examples, the voice utterance portion  328   b  can include other information, such as detected pauses (e.g., periods of non-speech) between words spoken by a user, as shown in  FIG.  3 F . The pauses may demarcate the locations of separate commands, keywords, or other information spoke by the user within the voice utterance portion  328   b.    
     In some embodiments, the media playback system  100  is configured to temporarily reduce the volume of audio content that it is playing while detecting the activation word portion  557   a.  The media playback system  100  may restore the volume after processing the voice input  328 , as shown in  FIG.  3 F . Such a process can be referred to as ducking, examples of which are disclosed in U.S. patent application Ser. No. 15/438,749, incorporated by reference herein in its entirety. 
     IV. Data transfer using sound signals 
       FIG.  4    is a diagrammatic representation of an environment in which a playback device  410  is arranged to transmit data using sound signals to another device. The playback device  410  has the same construction as the playback device  110   a  ( FIG.  1 C ). In particular, the playback device  410  includes at least one transducer for generating sound signals, for example a tweeter for generating relatively high-frequency sound signals, such as sounds with frequencies above about 2 kHz, and/or sounds with frequencies up to about 22 kHz. The playback device  410  is configured to implement a method according to  FIG.  5    to transmit data using sound signals to another device. In this example, the another device is a control device  430  which has the same construction as control device  130   a  ( FIG.  1 H ). 
       FIG.  5    is a flow chart of a method by which data is transmitted using sound signals. The method may, for example, be performed by a playback device such as the playback devices described throughout this disclosure, though the method is more generally applicable and is not limited to being performed by playback devices. The method of  FIG.  5    can be applied to the transmission of data using ultrasonic sound signals, using transducers that are primarily designed for transmitting audio sound signals, although can also be applied more generally in the transmission of data using sound signals. 
     Referring to  FIG.  5   , a block of data is first encoded, at S 510 , into a sequence of symbols to be transmitted. A block of data is a portion of digital data for transmission in a message and may have a predetermined fixed length, for example a fixed number of bits, such as 8, 16, 32 or 64 bits, or have an arbitrary length corresponding the length of the data bits to be transmitted in the message. Each symbol corresponds to a predetermined number of bits in the block, for example, 1, 2, 4, 8, 16 or more. Should the number of bits in the message not match an integer number of symbols, padding may be used to expand the block of data to a length corresponding to an integer number of symbols. Any suitable padding method may be used, for example, zero-padding in which zeroes are added to end of the message to give it a length of an integer number of symbols. Similarly, if the data in the message comprises more bits than can fit in one block, the message may be divided over two or more blocks for transmission. 
     As mentioned above, each symbol to be transmitted represents a predetermined number of bits of data within the data block. The number of bits represented by each symbol depends on the modulation scheme by which the symbols are to be modulated onto a carrier signal. 
     The symbols to be transmitted are modulated, at S 520 , onto a sonic carrier signal to generate modulated data. The symbols may be modulated onto the sonic carrier signal using any suitable modulation scheme. Examples of modulation schemes include amplitude-shift keying (ASK), phase-shift keying (PSK), and quadrature amplitude modulation (QAM). In the example of  FIG.  4   , the playback device  410  modulates symbols onto a sonic carrier wave using 16-QAM, in which each symbol corresponds to four bits of binary data. For other modulation methods, symbols may correspond to more or fewer than four bits. 
     In the example of  FIG.  4   , the sonic carrier signal is an ultrasonic carrier signal. An ultrasonic sound signal has a frequency that is higher than the highest frequency of sound that is audible to an average person, for example higher than about 20 kHz. The highest audible sound varies between individuals, so for the purpose of the present disclosure, an ultrasonic sound signal may be considered to have a frequency that remains above about 20 kHz for the duration of the sound signal. 
     The modulated data is transmitted using a transducer, such as an electroacoustic transducer. In this example, the tweeter of the playback device  410  is operable to generate sound signals having a frequency of between about 2 kHz and about 22 kHz, and therefore can be operated to generate ultrasonic sound signals with a frequency of between about 20 kHz and 22 kHz. Transducers, such as tweeters, may be manufactured to be able to generate sound signals outside the audible range of human hearing in order to reduce detrimental effects associated with roll-off near the extremes of the audible hearing range. However, such transducers may not be primarily designed to transmit ultrasonic signals, and may suffer from detrimental effects when operating near the top end of the operable frequency range, particularly as this range may not be used during audio reproduction (for example 44.1 kHz “CD Quality” PCM sound signals are normally low-pass filtered with cut off of around 20 kHz). The methods described herein may improve at least one of the reliability and robustness of data transmission by such transducers. 
     The modulated data is transmitted using the ultrasonic transducer by transmitting, at S 530 , a portion of the modulated data for a first duration. In this example, the first duration corresponds to a duration of one symbol in the modulated data. However, the first duration may in general be any predetermined duration, for example corresponding to a predetermined number of symbols in the modulated data. 
     After transmission for the first duration, transmission is paused, at S 540 , for a second duration. In this example, the second duration is the same as the first duration; one symbol length. However, the second duration may in general be a predetermined duration, and may be substantially the same as, or different from, the first duration. 
     After the pause at S 540 , at S 550  it is determined whether there remains modulated data awaiting transmission, if there is the transmitting and pausing of S 530  and S 540  is repeated with further portions of the modulated data, until all modulated data for transmission has been transmitted. 
     Transmission of data using the method of  FIG.  5    results in a sonic carrier signal carrying the modulated data which is intermittent, with gaps in which no symbols are transmitted. Pausing the transmission of a sonic carrier signal during data transmission may improve reliability and robustness of data transmission. In examples where ultrasonic signals are generated using an electroacoustic transducer that is primarily designed for transmitting audible sound signals (for example, the tweeter of playback device  410 ), a significant portion of the electrical energy supplied to the transducer may be converted to thermal energy. This thermal energy may affect the performance of the transducer. For example, thermal energy may increase the temperature of a diaphragm of the transducer, which may cause thermal stress in the diaphragm. This thermal stress may increase the impedance of the transducer, which may affect the operable frequency range of the playback device. Increasing the temperature of components of the transducer may also affect the material properties of components of the transducer (for example, elasticity of the transducer), which may further affect the performance of the transducer. Further still, transmitting sound signals near the edge of operable frequency range of a transducer may cause thermal damage to the transducer. The detrimental effects described above may be most prominent within particular frequency bands, depending on the properties of the transducer. A device may be programmed such that frequency bands associated with the most prominent detrimental effects are avoided. 
     Transmitting modulated data in portions separated by pauses allows components of the transducer to cool during the gaps in transmission. Allowing the components of the transducer to cool reduces the accumulation of thermal energy, and therefore at least partially mitigates the detrimental effects described above. The duration of the gaps (the second duration described above with reference to  FIG.  5   ) may be based on a characteristic of the electroacoustic transducer transmitting the data. For example, during manufacture or configuration of an electroacoustic transducer, a sufficient duration may be determined for mitigating the detrimental effects described above, and a playback device incorporating the transducer may then be programmed to pause transmission for the determined duration when sending data modulated on a sonic carrier signal. Alternatively, the duration of gaps may be based on characteristics of a device incorporating the electroacoustic transducer, which may include characteristics of one or more transducers of the device, characteristics of the circuitry or other physical components of the device, and/or other characteristics such as the intended use of the device, which may affect the duration, frequency, or other characteristics of data-carrying sound signals that the device is expected to transmit. The duration of gaps may be based on, for example, a product model incorporating the electroacoustic transducer. This may take into account the overall characteristics of the transducers incorporated into that product model. Additionally, or alternatively, the duration of each transmitted portion of modulated data may depend on a characteristic of a particular transducer or device. 
     As described above for  FIG.  5   , the gaps are regularly temporally spaced and/or of equal duration (corresponding to the first duration and/or second duration being fixed). In some embodiments the gaps may have different spacings and/or durations, for example having a predetermined sequence of first durations and second durations. 
     In some embodiments, a playback device may simultaneously perform audio reproduction from a media source and transmit modulated data using sound signals. For example, a playback device may simultaneously perform audio reproduction and transmit the modulated data using ultrasonic sound signals. In some examples, an audio signal and modulated data are simultaneously transmitted by a single electroacoustic transducer. Simultaneously transmitting data and audio signals by a single transducer may cause more thermal energy to be generated than transmitting data alone. A playback device may therefore be configured such that the duration of transmitted portions of modulated data, and/or the duration of pauses between the transmitted portions, depends on whether an audio signal is transmitted simultaneously with the modulated data. For example, a playback device may the duration of the pauses (the second duration) may be longer when an audio signal is transmitted simultaneously with the modulated data than when modulated data is transmitted without audio. 
     In some embodiments, a method of transmitting data in accordance with  FIG.  5    further includes processing the modulated data using a high pass filter prior to transmitting the modulated data. The high pass filter has a cut-off frequency that is less than or equal to a lowest frequency of the modulated data. In some cases, transitions between symbols and pauses in the modulated data, in which the sonic carrier signal is switched on or off, result in undesirable transient artefacts appearing in the signal. A sudden switching on or off of a carrier signal (for example a transition having a step-like profile in the time domain) has a Fourier transform with components over a range of frequencies, and these components may impact the data upon demodulation. In an example where data is modulated onto an ultrasonic carrier signal, the high-pass filter may have a cut-off frequency above the audible hearing range, for example about 20 kHz. Therefore, signal artefacts in the audible range will be removed from the signal, and will not be detectable by a human with an average hearing range. In embodiments where data is sent by a playback device that simultaneously performs audio reproduction, this may mitigate or prevent any detrimental effects to the listening experience. 
     In some embodiments, a header portion is transmitted on a sonic carrier signal, followed by modulated data corresponding to a block of data. Each block of data is therefore preceded by a header portion. A transmitted message may contain one or more blocks of data, each block preceded by a header portion and including a predetermined number of portions of modulated data. A receiving device is able to identify the beginning of a block of data by identifying the header portion preceding the block of data. The header portion has a predetermined duration that is different from the first duration (the duration of each portion of modulated data between pauses). In this way a start of a data transmission can be identified by searching for a received signal having the predetermined header duration. In some examples, the header portion is transmitted continuously, without any pauses or gaps in the sonic carrier signal. In such examples, identifying the header portion involves identifying a period of time in which the sonic carrier signal is continuously transmitted for the predetermined duration of the header portion. In other examples, a header portion may contain sub-portions separated by pauses, where each sub-portion has a different duration to the first duration. Furthermore, pauses between sub-portions of the header may have different durations to the pauses between portions of the data block. In such examples, a receiving device is able to identify a header portion, and hence identify the beginning of a block of data, by detecting this different pattern of transmission and pauses. 
     In addition to having the predetermined duration, a header portion may contain a predetermined sequence of symbols. A header portion may contain a plurality of symbols, for example two, three or four symbols, where the number of symbols is different to the number of symbols transmitted between pauses in the method of  FIG.  5   . 
     In the method of  FIG.  5   , the modulated block of data has a maximum signal amplitude. In some examples, a header portion comprises at least this maximum signal amplitude when modulated onto the sonic carrier signal. Including the maximum signal amplitude in the header portion allows a receiving device to determine a reference modulated signal amplitude for demodulating the signal. Various configurations of header portions are possible, and particular configurations may be appropriate for particular applications depending on factors such as the size of the associated data block and the method by which the data is encoded and/or modulated. A specific example will be described in more detail below for an example in which data is modulated using 16-QAM. 
       FIG.  6    shows a constellation diagram for an example of a 16-QAM modulation scheme. Each possible permutation of four consecutive binary bits is mapped to a point in the I-Q plane (where I is the in-phase component of the modulating signal and Q is the quadrature component of the modulating signal). It is noted that the mapping of  FIG.  6    is only an example, other mappings are possible. The phase and magnitude of a vector from the origin to each point in the diagram (in other words, a phasor for each point) corresponds to a phase and amplitude of the modulated sonic carrier signal. Each symbol corresponds to one of the points in the diagram, and hence represents, or conveys, four bits of data. It is observed that, in this example, the sonic carrier signal has three different amplitude states, corresponding to the magnitudes of the three phasors shown as arrows in  FIG.  6   . A maximum carrier signal amplitude corresponds to one of the four symbols conveying bit sequences 1011, 0011, 1111, 0111 (corresponding to the points furthest from the origin). A minimum carrier signal amplitude corresponds to one of the four symbols conveying bit sequences 1000, 0000, 1100, 0100 (corresponding to the points closest to the origin). An intermediate carrier signal amplitude corresponds to one of the remaining eight symbols. In some embodiments, a header portion may include at least one symbol of each amplitude. For example, using the mapping of  FIG.  6   , the header portion 111100001010 contains three symbols, one of each possible carrier signal amplitude (corresponding to the three arrows in  FIG.  8   ). In other examples a header portion may include multiple symbols of each amplitude. For example, the header portion 1111000010100101 contains four symbols, two being intermediate amplitude symbols (corresponding to the four empty circles in  FIG.  8   ). The header portion 1111000010100101 includes every combination of amplitudes of the in-phase and quadrature components. A receiving device may use the amplitudes of the signals or the signal components in the header portion to determine reference amplitudes for the modulated data following the header portion. 
     In addition to being used to identify the beginning of a block of data, and/or determining a reference amplitude for a received signal, a header portion may be used to determine a timing of a received signal, as will be described in more detail hereafter. A header portion may further be used to transmit meta-data for the associated block of data. For example, a header portion may convey data indicating a pattern of transmission and pausing (for example the length of the first duration and the second duration) for the following data portion, which the transmitting device may adjust dynamically. In an embodiment such as that of  FIG.  4   , in which a playback device transmits data using ultrasonic sound signals, the playback device may use a first pattern of transmission and pausing when audio reproduction is performed simultaneously, and may use a second pattern of transmission and pausing when no audio reproduction is performed simultaneously. A header portion associated with a block of data may include data indicating which pattern will be used for the block, such that a receiving device can process the signal appropriately. 
     In some embodiments, a tail portion is transmitted on the sonic carrier signal after a block of data. The tail portion has a predetermined duration that is different from the duration of each portion of the modulated data. In some examples, each block of data is transmitted with a header portion and a tail portion. In a further example, a tail portion may only be transmitted at the end of an entire message (which may contain several blocks of data, as discussed above). In this way, messages of varying lengths may be easily identified by a receiving device. 
     In examples where a header portion and a tail portion are transmitted, the tail portion may have the same duration as the corresponding header portion or a different duration to the corresponding header portion. A tail portion may contain a different sequence of symbols to a corresponding header portion, allowing a receiving device to distinguish the tail portion and the header portion. A tail portion may, for example, contain the reverse bit sequence of the header portion, or may contain the reverse symbol sequence of the header portion. A tail portion may contain at least the maximum signal amplitude of the modulated data block when modulated onto the sonic carrier signal, and may contain every signal amplitude of the modulated data block, or every combination of amplitudes of in-phase and quadrature components. For example, using the symbol mapping of  FIG.  6   , the tail portion conveying the sequence of bits 1010010100001111 contains at least one symbol of each amplitude, and one symbol for each combination of amplitudes of the in phase and quadrature components. This sequence 1010010100001111 is the reverse bit sequence of the header portion sequence 1111000010100101. The sequence 0101101000001111 is the reverse symbol sequence of the header portion sequence 1111000010100101. 
     Devices primarily designed for audio reproduction typically use a sample rate of 44.1 kHz or 48 kHz, which are sufficient for reconstructing frequencies of up to 22.05 kHz and 24 kHz respectively, due to the Nyquist-Shannon sampling theorem. However, the reconstructed signal is low-pass filtered with a cut off point below this frequency to reduce the effects of aliasing, so that for example, the reconstructed audio has reduced signal power above about 20 kHz. It has been found that electroacoustic transducers can operate at frequencies above 20 kHz and this allows the use of the band above 20 kHz for data transmission, without needing significant changes to the other electronics in the signal chain, which is designed to operate on data sampled at least at 44.1 kHz. Accordingly, these sampling rates are sufficient for transmitting data using ultrasonic sound signals with frequencies of up to 22.05 kHz and 24 kHz respectively. It will be appreciated that audio formats with sampling rates greater than 48 kHz, such as 92 kHz or 192 kHz may allow greater bandwidth for data transmission in the band above 20 kHz, subject to the ability of the transducer to reproduce those frequencies at the power level required for data transmission. 
     The rate at which symbols may be transmitted is lower than the frequency of the ultrasonic carrier signal, such that the amplitude and phase of the carrier signal can be correctly recovered for each symbol. In examples, the symbol rate may be between 10 Hz and 100 Hz. Although higher symbol rates may be used, this increases signal-to-noise ratio (SNR) and make demodulation of the signal more challenging. For examples in which QAM-16 modulation is used, the data rate (bit rate) is four times the symbol rate. The data rate may be, for example, between 40 and 400 Hz. It is noted that some devices are capable of high-resolution audio reproduction using higher sampling rates, such as 96 kHz sampling. For such devices, higher carrier signal frequencies may be realised (provided the transducer is capable of generating such signals), and accordingly higher symbol rates and data rates may be achieved. 
       FIG.  4    shows a receiving device configured to receive data. The receiving device in this example is a smartphone configured for use as a control device  430 . The control device  430  has components substantially the same as those of the control device  130   a  shown in  FIG.  1 H . The control device  430  is configured to receive data according to the method of  FIG.  7   . 
     As shown in  FIG.  7   , a method of receiving data includes a microphone receiving, at S 710 , sound containing a block of data modulated on an intermittent carrier signal. The block of data may be modulated according to any suitable modulation scheme, as discussed above with reference to data transmission. In the example of  FIG.  4   , the playback device  410  modulates data using 16-QAM. 
     The received sound is sampled, at S 720 , to generate a sampled data stream. A sampled data stream includes signal values at each of a set of sampling points, where the sampling points are separated based on a predetermined sampling rate (for example, 44.1 kHz or 48 kHz). The sampling rate may be the same as the sampling rate of a device transmitting the block of data. Matching the sampling rates between transmitting and receiving devices is not necessary for the present method to work, as long the receiving sampling rate is at least twice the Nyquist frequency of the modulated data (the Nyquist frequency in this case being the maximum frequency of the modulated data signal). 
     The sampled data stream is demodulated such that the data can be decoded and further processed. Demodulating the sampled data stream includes demodulating, at S 730 , a portion of the sampled data stream corresponding to a first duration in which the intermittent ultrasonic carrier signal is present, and then disregarding, at S 740 , a portion of the sampled data stream corresponding to a second duration in which the intermittent ultrasonic carrier signal is not present. In the example of data modulated using a QAM modulation scheme, demodulating each portion of the sampled data stream involves multiplication of the portion by cosine and sine signals and lowpass filtering the results to recover baseband I and Q values. The baseband I and Q values correspond to symbols, each encoding a predetermined number of data bits in accordance with a mapping such as that of  FIG.  6   . 
     It is then determined at step S 750  whether further data is awaiting demodulation. If there is further data the demodulating at S 730  and disregarding at S 740  are repeated. 
     As discussed above, portions of the sampled data stream that correspond to pauses in transmission of the sonic carrier signal are disregarded. In some examples, a receiving device may detect such portions of the sampled data stream before or during the demodulation process, for example by determining that the amplitude of the sonic carrier signal is close to zero. In other examples, a receiving device may use header and/or tail portions in the received sound signal to determine which portions of the data stream to disregard. This approach may result in reduced processing by the receiving device, as minimal processing is required for the portions of the data stream determined to be disregarded. 
       FIG.  8    shows a waveform of an example received sound signal transmitted using the method of  FIG.  5   . The received signal contains three blocks of data  860 , each block including four symbols  862 . The symbols in each block are separated by a pause  864  having a duration equal to one symbol. In this example, no header portion or tail portion is transmitted for purposes of illustration, and each of block of data is the same to demonstrate the repeatable nature of the data transmission. 
       FIG.  9    shows in phase and quadrature components for a demodulated sound signal waveform from  FIG.  8   , containing four 16-QAM symbols, where the four symbols are separated by a pause having an equal duration to one symbol. The solid line represents the in phase components, and the dashed line represents the quadrature components. The horizontal axis depicts the sample numbers from data sampled at a rate of 44.1 kHz in this example. The symbol rate is 40 Hz, corresponding to a data rate of 160 Hz. Using the mapping of symbols shown in  FIG.  6   , the demodulated data block conveys the bit sequence 1010011010000100. 
     In some embodiments, a method of receiving data in accordance with  FIG.  7    further includes processing the received sound with a high pass filter before sampling the received sound. The high pass filter has a cut-off frequency that is less than or equal to a lowest frequency of the expected sonic carrier signal, for example less than about 20 kHz. In some cases, transitions in which the sonic carrier signal is switched on or off result in undesirable transient artefacts being present in the signal. These artefacts may originate during transmission of the data signal, as described above, or may originate at the receiver. In either case, the data within the signal received by the electronics of the receiving device may be obscured by such artefacts. Processing the received sound with a high-pass filter may reduce such artefacts, improving the reliability of demodulation of the sampled data stream. In an example where data is modulated onto an ultrasonic carrier signal, a high pass filter may also be used to extract the ultrasonic signal from audible background sound, for example sound generated by audio reproduction by one or more playback devices. 
     As discussed above, in some embodiments a block of data modulated onto a sonic carrier signal is preceded by a header portion having a predetermined duration which is different from the duration of each portion of data transmitted between pauses in the sonic carrier signal. Accordingly, a receiver device performing the method of  FIG.  7    may detect a header portion in the received sound, for example by detecting a continuous transmission of the sonic carrier having the predetermined duration of a header portion. The receiver device may use the header portion to identify the beginning of a block of data. Identifying the beginning of a block of data by detecting a header portion results in a coarse estimate of a timing of the block of data. A coarse timing estimate may be accurate, for example, to within a fraction of a symbol, for example a fifth or a tenth of a symbol. The header portion may further be used to determine a fine timing estimate of the block of data. A fine timing estimate may be accurate to within the duration of a few samples or the interval between individual samples. For example, a header portion may include a predetermined sequence of symbols. By performing a cross-correlation between a received header portion and the predetermined sequence of symbols for a set of candidate timing offsets, a fine timing may be determined, corresponding to the candidate timing offset giving a maximum value of the cross-correlation. Determining a fine timing estimate of a block of data may allow the data to be demodulated and decoded more accurately than if only a coarse timing estimate is used. 
     In some embodiments, receiving a block of data includes processing a header portion to determine a reference modulated signal value. The reference signal value may be an amplitude. Determining a reference signal amplitude may be necessary for examples where data is modulated using a modulation scheme involving amplitude modulation, for example QAM or ASK. A header portion may, for example, contain at least a maximum signal amplitude of the modulated signal. Determining a maximum signal amplitude may involve determining the maximum signal amplitude in the received header portion. In other examples, a header portion may include every signal amplitude within a modulated signal, for example as discussed above with reference to  FIG.  6   . In this case, more than one reference signal amplitude may be determined, for example by measuring the signal amplitudes for different symbols in the header portion. 
     In addition to being preceded by a header portion, a block of data may be followed by a tail portion. In addition to, or as an alternative to, detecting a header portion, the receiving device may detect a tail portion in the received sound. In some examples, a receiving device may use the tail portion to identify the end of a block of data. In some examples, a tail portion may only be transmitted at the end of an entire message (which may contain several blocks of data, as discussed above). A receiving device may then be able to identify individual messages of arbitrary length. 
     The tail portion may be used to determine coarse and fine timing estimates of the block of data, in a similar manner to the header portion described above. By combining the estimates determined using the header and the tail respectively (for example, by taking an average such as an arithmetic mean), a more accurate estimate of the timing of the block of data may be determined. Similarly, the tail portion may be used to determine one or more reference modulated signal values. By combining the reference signal values determined using the header portion and the tail portion, a more accurate reference signal value may be determined. Further, if the reference signal value changes between the header and tail portions, an interpolated varying reference signal value may be determined for the block of data. For example, a linearly-varying reference signal value may be assumed. 
     The methods described above may be used to transfer data between devices using sound signals. In the embodiment of  FIG.  4   , a playback device  410  transfers data to a receiving device, which in this example is a control device  430  similar to that discussed above with reference to  FIG.  1 H , and is connected via a network to a playback system containing the playback device  410 . In the illustrated example, a listener  403  holding control device  430  walks into the room  401  in which the playback device  410  is located. The playback device  410  is configured to transmit data blocks corresponding to an acoustic identifier of the playback device  410 , using the method described above with reference to  FIG.  5   . In this example, an acoustic identifier is a sequence of symbols associated with the playback device  410  which allows a receiving device to identify the playback device  410 . In this example, the playback device  410  is configured to transmit the acoustic identifier at regular intervals, though in other examples, a playback device may be configured to transmit an acoustic identifier based on a trigger event, for example when the playback device is switched on, or in response to receiving a control signal from a control device. 
     An acoustic identifier may be transmitted in a single block, or may be transmitted in several blocks. A playback device may have a predetermined acoustic identifier, for example a unique predetermined acoustic identifier that is different from an acoustic identifier of any other playback device. Alternatively, a playback device may have an acoustic identifier that is assigned dynamically, for example to ensure that playback devices in a playback system have different acoustic identifiers. An acoustic identifier of a playback device may therefore change as a configuration of the playback system changes. A dynamically-assigned acoustic identifier may be assigned automatically by a computing system associated with a playback system. Dynamic allocation of acoustic identifiers allows for acoustic identifiers to be shorter in comparison with unique predetermined acoustic identifiers, which may be advantageous in terms of reliability and efficiency of transmitting and receiving the acoustic identifiers. 
     An acoustic identifier can be used to identify a playback device, a playback zone containing the playback device, and/or a zone group of the playback zone containing the playback device. In some examples, playback devices within the same playback zone and/or zone group may transmit the same acoustic identifier. Playback devices within a playback zone and/or zone group may transmit the same acoustic identifier in synchrony, or asynchronously. In some examples, a subset of playback devices within a playback zone and/or zone group may transmit an acoustic identifier. In further examples, two or more playback devices may be bonded or paired to form a consolidated player or a bonded player, as described in detail above with reference to  FIGS.  1 I- 1 K . In such cases, one or more of the bonded or paired playback devices may be arranged to transmit an acoustic identifier for the bonded or consolidated player. In some examples, two or more of the bonded or paired playback devices may take turns to transmit an acoustic identifier. If the acoustic identifiers are transmitted frequently, taking turns to transmit an acoustic identifier may mitigate any detrimental effects to the playback devices or the audio reproduction by the playback devices, for example caused by an accumulation of thermal energy in transducers of the playback devices. 
     The control device  430  receives the acoustic identifier using the method described above with reference to  FIG.  7   . The control device  430  may be configured to perform various actions in response to receiving the acoustic identifier from the playback device  410 . For example, the control device  430  may display a user interface associated with the playback device  410 , or a playback zone or zone group containing the playback device  410 , such that the listener  403  is able to control audio reproduction by the playback device  410 . As the listener  403  walks from room to room, the control device  430  may automatically update the user interface to indicate that the listener  403  has entered a region associated with a new playback device, playback zone, or zone group, such that the listener  403  is able to control audio reproduction in whichever room the listener  403  is currently located in. 
     Other forms of data may also be transferred between the playback device  410  and the control device  430  using the methods of  FIGS.  5  and  7   . For example, the data may comprise authentication information for a playback system comprising the playback device  410 , which may then be used by the control device  430  to join a network of the playback system. The use of a sonic channel to transmit the data may allow the data to be received over the sonic channel while the control device remains connected to another network than that used by the playback system or may allow security to be enhanced by the use of additional communication channels. 
       FIG.  10    shows an example in which a first playback device  1010   a  transfers data to a second playback device  1010   b  during a setup process. In this example, the first playback device  1010   a  and the second playback device  1010   b  are connected via a network to form part of a playback system, but are initially not paired. The first playback device  1010   a  is placed in a setup mode, for example by a user  1003  of a control device  1030 . The second playback device  1010   b  is placed in a receiving mode in which the second playback device  1010   b  listens for data-conveying sound signals. The first playback device  1010   a  sends data using the method of  FIG.  5   , indicating that the first playback device  1010   a  is ready to pair. In this example, the data transmitted by the first playback device  1010   a  includes an acoustic identifier of the first playback device  1010   a.  The second playback device  1010   b  receives the data using the method of  FIG.  7   . In response to receiving the data from the first playback device  1010   a,  the second playback device  1010   b  sends a message to the first playback device  1010   a  via the network (or alternatively, via a further sound signal), using the acoustic identifier received from the first playback device  1010   a  to identify the first playback device  1010   a,  and enters a pairing mode with the first playback device  1010   a.    
     Once the first playback device  1010   a  and the second playback device  1010   b  have entered a pairing mode, the pairing or bonding of the first playback device  1010   a  and the second playback device  1010   b  is configurable, for example by the user  1003  of the control device  1030 . In this example, the first playback device  1010   a  and the second playback device  1010   b  are to be configured as a stereo pair, with the first playback device  1010   a  as a right speaker and the second playback device  1010   b  as a left speaker. It will be appreciated that other configurations are possible, for example the two playback devices may be configured as a consolidated player. 
     Methods such as that described with reference to  FIG.  10    may be performed by multiple playback devices, for example resulting in automatic formation of new playback zones and/or new bonded or consolidated playback devices. In some examples, certain models of playback device are configured to be paired in a default configuration, for example if a first playback device is designed for relatively low-frequency audio reproduction (for example, a playback device containing a subwoofer) and a second playback device is designed for relatively high-frequency audio reproduction (for example, a playback device containing a woofer and/or a tweeter). In such an example, receipt of setup data from the first playback device by the second playback device may cause the second playback device to automatically pair with the first playback device, forming a bonded playback device in the default configuration. 
     In another example, a playback device may transmit data to a receiving device using the methods described herein to indicate the nature of a hardware fault or other type of technical fault. Known types of fault may each be assigned a unique fault code that can be transmitted by the playback device. For example, a playback device may detect a hardware fault and enter a fault mode. The playback device may indicate that it has entered the fault mode, for example, by illuminating a dedicated light, or changing a color of a light on the playback device. Alternatively, a playback device may indicate that it has entered a fault mode using an audible signal, for example a beeping sound. On noticing that the playback device has entered a fault mode, a user of a receiving device (for example, a smartphone, tablet or laptop computer) may connect to a technical support service, for example using a voice call, using a dedicated application, or via a user interface of a more general application associated with the playback device. The received data may be demodulated and decoded by the receiving device, or by the technical support service. The receiving device or the technical support service may determine the nature of the hardware fault from the demodulated and decoded data. Depending on the nature of the fault, the receiving device or technical support service may provide instructions to the user to remedy the fault, or alternatively connect the user to an appropriate member of a technical support team. Transmission of data indicating the nature of a technical fault as described may negate the need for a human user to describe the fault to a person, thus saving time for the user and the technical support service, as well as increasing reliability by ensuring that a fault is not detected erroneously. This may allow data of a fault to be transmitted when the fault means that a network interface of the device experiencing the fault is inoperable or operating erroneously, which can be useful when a device has a limited user interface to indicate the nature of the fault. 
     IV. Conclusion 
     The above discussions relating to playback devices, controller devices, playback zone configurations, and media content sources provide only some examples of operating environments within which functions and methods described below may be implemented. Other operating environments and configurations of media playback systems, playback devices, and network devices not explicitly described herein may also be applicable and suitable for implementation of the functions and methods. 
     The description above discloses, among other things, various example systems, methods, apparatus, and articles of manufacture including, among other components, firmware and/or software executed on hardware. It is understood that such examples are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of the firmware, hardware, and/or software aspects or components can be embodied exclusively in hardware, exclusively in software, exclusively in firmware, or in any combination of hardware, software, and/or firmware. Accordingly, the examples provided are not the only ways) to implement such systems, methods, apparatus, and/or articles of manufacture. 
     Additionally, references herein to “embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one example embodiment of an invention. The appearances of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. As such, the embodiments described herein, explicitly and implicitly understood by one skilled in the art, can be combined with other embodiments. 
     The specification is presented largely in terms of illustrative environments, systems, procedures, steps, logic blocks, processing, and other symbolic representations that directly or indirectly resemble the operations of data processing devices coupled to networks. These process descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, it is understood to those skilled in the art that certain embodiments of the present disclosure can be practiced without certain, specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the embodiments. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the foregoing description of embodiments. 
     When any of the appended claims are read to cover a purely software and/or firmware implementation, at least one of the elements in at least one example is hereby expressly defined to include a tangible, non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on, storing the software and/or firmware.