Patent Publication Number: US-2023164504-A1

Title: Calibration based on audio content

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. Non Provisional Pat. Application No. 17/316,371, filed on May 10, 2021, entitled “Calibration Based on Audio Content,” which is incorporated herein by reference in its entirety. 
     U.S. non provisional Patent Application No. 17/316,371 claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. Non Provisional Pat. Application No. 17/129,670, filed on Dec. 21, 2020, entitled “Calibration Based on Audio Content,” and issued as U.S. Pat. No. 11,006,232 on May 11, 2021, which is incorporated herein by reference in its entirety. 
     U.S. Non Provisional Pat. Application No. 17/129,670 claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. Non Provisional Pat. Application No. 16/944,884, filed on Jul. 31, 2020, entitled “Calibration Using Listener Locations,” and issued as U.S. Pat. No. 11,184,726 on Nov. 23, 2021, which is incorporated herein by reference in its entirety. 
     U.S. Non Provisional Pat. Application No. 16/944,884 claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. Non-Provisional Pat. Application No. 16/542,418, filed on Aug. 16, 2019, entitled “Calibration Based on Grouping,” and issued as U.S. Pat. No. 10,735,879 on Aug. 4, 2020, which is incorporated herein by reference in its entirety. 
     U.S. Non Provisional Pat. Application No. 16/542,418 claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. Non Provisional Pat. Application No. 16/011,402, filed on Jun. 18, 2018, entitled “Calibration Based on Audio Content Type,” and issued as U.S. Pat. No. 10,390,161 on Aug. 20, 2019, which is incorporated herein by reference in its entirety. 
     U.S. Non Provisional Pat. Application No. 16/011,402 claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. Non Provisional Pat. Application No. 15/005,853, filed on Jan. 25, 2016, entitled “Calibration with Particular Locations,” and issued as U.S. Pat. No. 10,003,899 on Jun. 19, 2018, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The 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 2003, when SONOS, Inc. filed for one of its first patent applications, entitled “Method for Synchronizing Audio Playback between Multiple Networked Devices,” and began offering a media playback system for sale in 2005. The Sonos Wireless HiFi System enables people to experience music from many sources via one or more networked playback devices. Through a software control application installed on a smartphone, tablet, or computer, one can play what he or she wants in any room that has a networked playback device. Additionally, using the controller, for example, different songs can be streamed to each room with a playback device, rooms can be grouped together for synchronous playback, or the same song can be heard in all rooms synchronously. 
     Given the ever growing interest in digital media, there continues to be a need to develop consumer-accessible technologies to further enhance the listening experience. 
    
    
     
       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 where: 
         FIG.  1    shows an example media playback system configuration in which certain embodiments may be practiced; 
         FIG.  2    shows a functional block diagram of an example playback device; 
         FIG.  3    shows a functional block diagram of an example control device; 
         FIG.  4    shows an example controller interface; 
         FIG.  5    shows an example control device; 
         FIG.  6    shows a smartphone that is displaying an example control interface, according to an example implementation; 
         FIG.  7    illustrates an example movement through an example environment in which an example media playback system is positioned; 
         FIG.  8    illustrates an example chirp that increases in frequency over time; 
         FIG.  9    shows an example brown noise spectrum; 
         FIGS.  10 A and  10 B  illustrate transition frequency ranges of example hybrid calibration sounds; 
         FIG.  11    shows a frame illustrating an iteration of an example periodic calibration sound; 
         FIG.  12    shows a series of frames illustrating iterations of an example periodic calibration sound; 
         FIG.  13    shows an example flow diagram to facilitate the calibration of one or more playback devices by determining multiple calibrations; 
         FIG.  14    shows a smartphone that is displaying an example control interface, according to an example implementation; 
         FIG.  15    shows an example flow diagram to facilitate applying one of multiple calibrations to playback; 
         FIG.  16    shows an example flow diagram to facilitate the calibration of playback devices using a recording device; 
         FIG.  17    shows a smartphone that is displaying an example control interface, according to an example implementation; 
         FIG.  18    shows a smartphone that is displaying an example control interface, according to an example implementation; 
         FIG.  19    shows a smartphone that is displaying an example control interface, according to an example implementation; 
         FIG.  20    shows a smartphone that is displaying an example control interface, according to an example implementation; 
         FIG.  21    shows a smartphone that is displaying an example control interface, according to an example implementation; and 
         FIG.  22    shows a smartphone that is displaying an example control interface, according to an example implementation. 
     
    
    
     The drawings are for the purpose of illustrating example embodiments, but it is understood that the inventions are not limited to the arrangements and instrumentality shown in the drawings. 
     DETAILED DESCRIPTION 
     I. Overview 
     Embodiments described herein involve, inter alia, techniques to facilitate calibration of a media playback system. Some calibration procedures contemplated herein involve a recording devices (e.g., a control devices) of a media playback system detecting sound waves (e.g., one or more calibration sounds) that were emitted by one or more playback devices of the media playback system. A processing device, such as one of the two or more recording devices or another device that is communicatively coupled to the media playback system, may analyze the detected sound waves to determine one or more calibrations for the one or more playback devices of the media playback system. Such calibrations may configure the one or more playback devices to a given listening area (i.e., the environment in which the playback device(s) were positioned while emitting the sound waves). 
     In some embodiments contemplated herein, the processing device may determine two or more calibrations for the one or more playback devices. Such calibrations may configure the one or more playback devices in different ways. In operation, one of the two or more calibrations may be applied to playback by the one or more playback devices, perhaps for different use cases. Example uses cases might include music playback or surround sound (i.e., home theater), among others. 
     Within examples, the calibration may include spectral and/or spatial calibration. For instance, the processing device may determine a first calibration that configures the one or more playback devices to a given listening area spectrally. Such a calibration may generally help offset acoustic characteristics of the environment and be applied during certain use cases, such as music playback. The processing device may also determine a second calibration that configures the one or more playback devices to a given listening area spatially (and perhaps also spectrally). Such a calibration may configure the one or more playback devices to one or more particular locations within the environment (e.g., one or more preferred listening positions, such as favorite seating location), perhaps by adjusting time-delay and/or loudness for those particular locations. This second calibration may be applied during other use cases, such as home theater. 
     In some examples, the one or more playback devices may switch among the two or more calibrations based on certain conditions, which may indicate various use cases. For instance, a playback device may apply a certain calibration based on the particular audio content being played back by the playback device. To illustrate, a playback device that is playing back an audio-only track might apply a first calibration (e.g., a calibration that includes spectral calibration) while a playback device that is playing back audio associated with video might apply a second calibration (e.g., a calibration that includes spatial calibration). If the audio content changes, the playback device might apply a different calibration. Alternatively, a certain calibration may be selected via input on a control device. 
     Other playback conditions might also cause the playback device to apply a certain calibration. For instance a playback device may apply a particular calibration based on the content source (e.g., a physical input or streaming audio). As another example, a playback device may apply a particular calibration based on the presence of listeners (and perhaps that those listeners are in or not in certain locations). Yet further, a playback device may apply a particular calibration based on a grouping that playback device is a member of (or perhaps based on the playback device being not a member of the grouping). Other examples are possible as well. 
     Acoustics of an environment may vary from location to location within the environment. Because of this variation, some calibration procedures may be improved by positioning the playback device to be calibrated within the environment in the same way that the playback device will later be operated. In that position, the environment may affect the calibration sound emitted by a playback device in a similar manner as playback will be affected by the environment during operation. 
     Further, some example calibration procedures may involve one or more recording devices detecting the calibration sound at multiple physical locations within the environment, which may further assist in capturing acoustic variability within the environment. To facilitate detecting the calibration sound at multiple points within an environment, some calibration procedures involve a moving microphone. For example, a microphone that is detecting the calibration sound may be moved through the environment while the calibration sound is emitted. Such movement may facilitate detecting the calibration sounds at multiple physical locations within the environment, which may provide a better understanding of the environment as a whole. 
     As indicated above, example calibration procedures may involve a playback device emitting a calibration sound, which may be detected by multiple recording devices. In some embodiments, the detected calibration sounds may be analyzed across a range of frequencies over which the playback device is to be calibrated (i.e., a calibration range). Accordingly, the particular calibration sound that is emitted by a playback device covers the calibration frequency range. The calibration frequency range may include a range of frequencies that the playback device is capable of emitting (e.g., 15 - 30,000 Hz) and may be inclusive of frequencies that are considered to be in the range of human hearing (e.g., 20 - 20,000 Hz). By emitting and subsequently detecting a calibration sound covering such a range of frequencies, a frequency response that is inclusive of that range may be determined for the playback device. Such a frequency response may be representative of the environment in which the playback device emitted the calibration sound. 
     In some embodiments, a playback device may repeatedly emit the calibration sound during the calibration procedure such that the calibration sound covers the calibration frequency range during each repetition. With a moving microphone, repetitions of the calibration sound are continuously detected at different physical locations within the environment. For instance, the playback device might emit a periodic calibration sound. Each period of the calibration sound may be detected by the recording device at a different physical location within the environment thereby providing a sample (i. e., a frame representing a repetition) at that location. Such a calibration sound may therefore facilitate a space-averaged calibration of the environment. When multiple microphones are utilized, each microphone may cover a respective portion of the environment (perhaps with some overlap). 
     Yet further, the recording devices may measure both moving and stationary samples. For instance, while the one or more playback devices output a calibration sound, a recording device may move within the environment. During such movement, the recording device may pause at one or more locations to measure stationary samples. Such locations may correspond to preferred listening locations. In another example, a first recording device and a second recording device may include a first microphone and a second microphone respectively. While the playback device emits a calibration sound, the first microphone may move and the second microphone may remain stationary, perhaps at a particular listening location within the environment (e.g., a favorite chair). 
     Example techniques may involve determining two or more calibrations and/or applying a given calibration to playback by one or more playback devices. A first implementation may include detecting, via one or more microphones, at least a portion of one or more calibration sounds as emitted by one or more playback devices of a zone during a calibration sequence. Such detecting may include recording first samples of the one or more calibrations sounds while the one or more microphones are in motion through a given environment and recording second samples of the one or more calibrations sounds while the one or more microphones are stationary at one or more particular locations within the given environment. The implementation may also include determining a first calibration for the one or more playback devices based on at least the first samples of the one or more calibrations sounds and determining a second calibration for the one or more playback devices based on at least the second samples of the one or more calibrations sounds. The implementation may further include applying at least one of (a) the first calibration or (b) the second calibration to playback by the one or more playback devices. 
     A second implementation may include displaying, via a graphical interface one or more prompts to move the control device within a given environment during a calibration sequence of a given zone that comprises one or more playback devices and detecting, via one or more microphones, at least a portion of one or more calibration sounds as emitted by the one or more playback devices during the calibration sequence. Such detecting may include recording first samples of the one or more calibrations sounds while the one or more microphones are in motion through the given environment and recording second samples of the one or more calibrations sounds while the one or more microphones are stationary at one or more particular locations within the given environment. The implementation may also include determining a first calibration for the one or more playback devices based on at least the first samples of the one or more calibrations sounds and determining a second calibration for the one or more playback devices based on at least the second samples of the one or more calibrations sounds. The implementation may further include sending at least one of the first calibration and the second calibration to the zone. 
     A third implementation includes a playback device receiving (i) a first calibration and (ii) a second calibration, detecting that the playback device is playing back media content in a given playback state, and applying the one of (a) the first calibration or (b) the second calibration to playback by the playback device based on the detected given playback state. 
     Each of the these example implementations may be embodied as a method, a device configured to carry out the implementation, or a non-transitory computer-readable medium containing instructions that are executable by one or more processors to carry out the implementation, among other examples. It will be understood by one of ordinary skill in the art that this disclosure includes numerous other embodiments, including combinations of the example features described herein. 
     While some examples described herein may refer to functions performed by given actors such as “users” and/or other entities, it should be understood that this description 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. 
     II. Example Operating Environment 
       FIG.  1    illustrates an example configuration of a media playback system  100  in which one or more embodiments disclosed herein may be practiced or implemented. The media playback system  100  as shown is associated with an example home environment having several rooms and spaces, such as for example, a master bedroom, an office, a dining room, and a living room. As shown in the example of  FIG.  1   , the media playback system  100  includes playback devices  102 - 124 , control devices  126  and  128 , and a wired or wireless network router  130 . 
     Further discussions relating to the different components of the example media playback system  100  and how the different components may interact to provide a user with a media experience may be found in the following sections. While discussions herein may generally refer to the example media playback system  100 , technologies described herein are not limited to applications within, among other things, the home environment as shown in  FIG.  1   . For instance, the technologies described herein may be useful in environments where multi-zone audio may be desired, such as, for example, a commercial setting like a restaurant, mall or airport, a vehicle like a sports utility vehicle (SUV), bus or car, a ship or boat, an airplane, and so on. 
     A. Example Playback Devices 
       FIG.  2    shows a functional block diagram of an example playback device  200  that may be configured to be one or more of the playback devices  102 - 124  of the media playback system  100  of  FIG.  1   . The playback device  200  may include a processor  202 , software components  204 , memory  206 , audio processing components  208 , audio amplifier(s)  210 , speaker(s)  212 , and a network interface  214  including wireless interface(s)  216  and wired interface(s)  218 . In one case, the playback device  200  may not include the speaker(s)  212 , but rather a speaker interface for connecting the playback device  200  to external speakers. In another case, the playback device  200  may include neither the speaker(s)  212  nor the audio amplifier(s)  210 , but rather an audio interface for connecting the playback device  200  to an external audio amplifier or audio-visual receiver. 
     In one example, the processor  202  may be a clock-driven computing component configured to process input data according to instructions stored in the memory  206 . The memory  206  may be a tangible computer-readable medium configured to store instructions executable by the processor  202 . For instance, the memory  206  may be data storage that can be loaded with one or more of the software components  204  executable by the processor  202  to achieve certain functions. In one example, the functions may involve the playback device  200  retrieving audio data from an audio source or another playback device. In another example, the functions may involve the playback device  200  sending audio data to another device or playback device on a network. In yet another example, the functions may involve pairing of the playback device  200  with one or more playback devices to create a multi-channel audio environment. 
     Certain functions may involve the playback device  200  synchronizing playback of audio content with one or more other playback devices. During synchronous playback, a listener will preferably not be able to perceive time-delay differences between playback of the audio content by the playback device  200  and the one or more other playback devices. 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 hereby incorporated by reference, provides in more detail some examples for audio playback synchronization among playback devices. 
     The memory  206  may further be configured to store data associated with the playback device  200 , such as one or more zones and/or zone groups the playback device  200  is a part of, audio sources accessible by the playback device  200 , or a playback queue that the playback device  200  (or some other playback device) may be associated with. The data may be stored as one or more state variables that are periodically updated and used to describe the state of the playback device  200 . The memory  206  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. Other embodiments are also possible. 
     The audio processing components  208  may include one or more digital-to-analog converters (DAC), an audio preprocessing component, an audio enhancement component or a digital signal processor (DSP), and so on. In one embodiment, one or more of the audio processing components  208  may be a subcomponent of the processor  202 . In one example, audio content may be processed and/or intentionally altered by the audio processing components  208  to produce audio signals. The produced audio signals may then be provided to the audio amplifier(s)  210  for amplification and playback through speaker(s)  212 . Particularly, the audio amplifier(s)  210  may include devices configured to amplify audio signals to a level for driving one or more of the speakers  212 . The speaker(s)  212  may include an individual transducer (e.g., a “driver”) or a complete speaker system involving an enclosure with one or more drivers. A particular driver of the speaker(s)  212  may include, for example, a subwoofer (e.g., for low frequencies), a mid-range driver (e.g., for middle frequencies), and/or a tweeter (e.g., for high frequencies). In some cases, each transducer in the one or more speakers  212  may be driven by an individual corresponding audio amplifier of the audio amplifier(s)  210 . In addition to producing analog signals for playback by the playback device  200 , the audio processing components  208  may be configured to process audio content to be sent to one or more other playback devices for playback. 
     Audio content to be processed and/or played back by the playback device  200  may be received from an external source, such as via an audio line-in input connection (e.g., an auto-detecting 3.5 mm audio line-in connection) or the network interface  214 . 
     The network interface  214  may be configured to facilitate a data flow between the playback device  200  and one or more other devices on a data network. As such, the playback device  200  may be configured to receive audio content over the data network from one or more other playback devices in communication with the playback device  200 , network devices within a local area network, or audio content sources over a wide area network such as the Internet. In one example, the audio content and other signals transmitted and received by the playback device  200  may be transmitted in the form of digital packet data containing an Internet Protocol (IP)-based source address and IP-based destination addresses. In such a case, the network interface  214  may be configured to parse the digital packet data such that the data destined for the playback device  200  is properly received and processed by the playback device  200 . 
     As shown, the network interface  214  may include wireless interface(s)  216  and wired interface(s)  218 . The wireless interface(s)  216  may provide network interface functions for the playback device  200  to wirelessly communicate with other devices (e.g., other playback device(s), speaker(s), receiver(s), network device(s), control device(s) within a data network the playback device  200  is associated with) in accordance with a communication protocol (e.g., any wireless standard including IEEE 802.11a, 802.11b, 802.11 g, 802.11n, 802.11ac, 802.15, 4G mobile communication standard, and so on). The wired interface(s)  218  may provide network interface functions for the playback device  200  to communicate over a wired connection with other devices in accordance with a communication protocol (e.g., IEEE 802.3). While the network interface  214  shown in  FIG.  2    includes both wireless interface(s)  216  and wired interface(s)  218 , the network interface  214  may in some embodiments include only wireless interface(s) or only wired interface(s). 
     In one example, the playback device  200  and one other playback device may be paired to play two separate audio components of audio content. For instance, playback device  200  may be configured to play a left channel audio component, while the other playback device may be configured to play a right channel audio component, thereby producing or enhancing a stereo effect of the audio content. The paired playback devices (also referred to as “bonded playback devices”) may further play audio content in synchrony with other playback devices. 
     In another example, the playback device  200  may be sonically consolidated with one or more other playback devices to form a single, consolidated playback device. A consolidated playback device may be configured to process and reproduce sound differently than an unconsolidated playback device or playback devices that are paired, because a consolidated playback device may have additional speaker drivers through which audio content may be rendered. For instance, if the playback device  200  is a playback device designed to render low frequency range audio content (i. e. a subwoofer), the playback device  200  may be consolidated with a playback device designed to render full frequency range audio content. In such a case, the full frequency range playback device, when consolidated with the low frequency playback device  200 , may be configured to render only the mid and high frequency components of audio content, while the low frequency range playback device  200  renders the low frequency component of the audio content. The consolidated playback device may further be paired with a single playback device or yet another consolidated playback device. 
     By way of illustration, SONOS, Inc. presently offers (or has offered) for sale certain playback devices including a “PLAY:1,” “PLAY:3,” “PLAY:5,” “PLAYBAR,” “CONNECT:AMP,” “CONNECT,” and “SUB.” Any other past, present, and/or future playback devices may additionally or alternatively be used to implement the playback devices of example embodiments disclosed herein. Additionally, it is understood that a playback device is not limited to the example illustrated in  FIG.  2    or to the SONOS product offerings. For example, a playback device may include a wired or wireless headphone. In another example, a playback device may include or interact with a docking station for personal mobile media playback devices. In yet another example, 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. 
     B. Example Playback Zone Configurations 
     Referring back to the media playback system  100  of  FIG.  1   , the environment may have one or more playback zones, each with one or more playback devices. The media playback system  100  may be established with one or more playback zones, after which one or more zones may be added, or removed to arrive at the example configuration shown in  FIG.  1   . Each zone may be given a name according to a different room or space such as an office, bathroom, master bedroom, bedroom, kitchen, dining room, living room, and/or balcony. In one case, a single playback zone may include multiple rooms or spaces. In another case, a single room or space may include multiple playback zones. 
     As shown in  FIG.  1   , the balcony, dining room, kitchen, bathroom, office, and bedroom zones each have one playback device, while the living room and master bedroom zones each have multiple playback devices. In the living room zone, playback devices  104 ,  106 ,  108 , and  110  may be configured to play audio content in synchrony as individual playback devices, as one or more bonded playback devices, as one or more consolidated playback devices, or any combination thereof. Similarly, in the case of the master bedroom, playback devices  122  and  124  may be configured to play audio content in synchrony as individual playback devices, as a bonded playback device, or as a consolidated playback device. 
     In one example, one or more playback zones in the environment of  FIG.  1    may each be playing different audio content. For instance, the user may be grilling in the balcony zone and listening to hip hop music being played by the playback device  102  while another user may be preparing food in the kitchen zone and listening to classical music being played by the playback device  114 . 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 zone where the playback device  118  is playing the same rock music that is being playing by playback device  102  in the balcony zone. In such a case, playback devices  102  and  118  may be playing the rock music in synchrony such that the user may seamlessly (or at least substantially seamlessly) enjoy the audio content that is being played out-loud while moving between different playback zones. Synchronization among playback zones may be achieved in a manner similar to that of synchronization among playback devices, as described in previously referenced U.S. Pat. No. 8,234,395. 
     As suggested above, the zone configurations of the media playback system  100  may be dynamically modified, and in some embodiments, the media playback system  100  supports numerous configurations. For instance, if a user physically moves one or more playback devices to or from a zone, the media playback system  100  may be reconfigured to accommodate the change(s). For instance, if the user physically moves the playback device  102  from the balcony zone to the office zone, the office zone may now include both the playback device  118  and the playback device  102 . The playback device  102  may be paired or grouped with the office zone and/or renamed if so desired via a control device such as the control devices  126  and  128 . On the other hand, if the one or more playback devices are moved to a particular area in the home environment that is not already a playback zone, a new playback zone may be created for the particular area. 
     Further, different playback zones of the media playback system  100  may be dynamically combined into zone groups or split up into individual playback zones. For instance, the dining room zone and the kitchen zone  114  may be combined into a zone group for a dinner party such that playback devices  112  and  114  may render audio content in synchrony. On the other hand, the living room zone may be split into a television zone including playback device  104 , and a listening zone including playback devices  106 ,  108 , and  110 , if the user wishes to listen to music in the living room space while another user wishes to watch television. 
     C. Example Control Devices 
       FIG.  3    shows a functional block diagram of an example control device  300  that may be configured to be one or both of the control devices  126  and  128  of the media playback system  100 . Control device  300  may also be referred to as a controller  300 . As shown, the control device  300  may include a processor  302 , memory  304 , a network interface  306 , and a user interface  308 . In one example, the control device  300  may be a dedicated controller for the media playback system  100 . In another example, the control device  300  may be a network device on which media playback system controller application software may be installed, such as for example, an iPhone™, iPad™ or any other smart phone, tablet or network device (e.g., a networked computer such as a PC or Mac™). 
     The processor  302  may be configured to perform functions relevant to facilitating user access, control, and configuration of the media playback system  100 . The memory  304  may be configured to store instructions executable by the processor  302  to perform those functions. The memory  304  may also be configured to store the media playback system controller application software and other data associated with the media playback system  100  and the user. 
     In one example, the network interface  306  may be based on an industry standard (e.g., infrared, radio, wired standards including IEEE 802.3, wireless standards including IEEE 802.1 1a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4G mobile communication standard, and so on). The network interface  306  may provide a means for the control device  300  to communicate with other devices in the media playback system  100 . In one example, data and information (e.g., such as a state variable) may be communicated between control device  300  and other devices via the network interface  306 . For instance, playback zone and zone group configurations in the media playback system  100  may be received by the control device  300  from a playback device or another network device, or transmitted by the control device  300  to another playback device or network device via the network interface  306 . In some cases, the other network device may be another control device. 
     Playback device control commands such as volume control and audio playback control may also be communicated from the control device  300  to a playback device via the network interface  306 . As suggested above, changes to configurations of the media playback system  100  may also be performed by a user using the control device  300 . The configuration changes may include adding/removing one or more playback devices 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. Accordingly, the control device  300  may sometimes be referred to as a controller, whether the control device  300  is a dedicated controller or a network device on which media playback system controller application software is installed. 
     The user interface  308  of the control device  300  may be configured to facilitate user access and control of the media playback system  100 , by providing a controller interface such as the controller interface  400  shown in  FIG.  4   . The controller interface  400  includes a playback control region  410 , a playback zone region  420 , a playback status region  430 , a playback queue region  440 , and an audio content sources region  450 . The user interface  400  as shown is just one example of a user interface that may be provided on a network device such as the control device  300  of  FIG.  3    (and/or the control devices  126  and  128  of  FIG.  1   ) and accessed by users to control a media playback system such as the media playback system  100 . Other 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 playback control region  410  may include selectable (e.g., by way of touch or by using a cursor) icons to cause playback devices in a selected playback zone or zone group to 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. The playback control region  410  may also include selectable icons to modify equalization settings, and playback volume, among other possibilities. 
     The playback zone region  420  may include representations of playback zones within the media playback system  100 . In some embodiments, the graphical representations of playback zones may be selectable to bring up additional selectable icons to manage or configure the playback zones in the media playback system, such as a creation of bonded zones, creation of zone groups, separation of zone groups, and renaming of zone groups, among other possibilities. 
     For example, as shown, a “group” icon may be provided within each of the graphical representations of playback zones. The “group” icon provided within a graphical representation of a particular zone may be selectable to bring up options to select one or more other zones in the media playback system to be grouped with the particular zone. Once grouped, playback devices in the zones that have been grouped with the particular zone will be configured to play audio content in synchrony with the playback device(s) in the particular zone. Analogously, a “group” icon may be provided within a graphical representation of a zone group. In this case, the “group” icon may be selectable to bring up options to deselect one or more zones in the zone group to be removed from the zone group. Other interactions and implementations for grouping and ungrouping zones via a user interface such as the user interface  400  are also possible. The representations of playback zones in the playback zone region  420  may be dynamically updated as playback zone or zone group configurations are modified. 
     The playback status region  430  may include graphical representations of audio content that is presently being played, previously played, or scheduled to play next in the selected playback zone or zone group. The selected playback zone or zone group may be visually distinguished on the user interface, such as within the playback zone region  420  and/or the playback status region  430 . The graphical representations may include track title, artist name, album name, album year, track length, and other relevant information that may be useful for the user to know when controlling the media playback system via the user interface  400 . 
     The playback queue region  440  may include graphical representations of audio content in a playback queue associated with the selected playback zone or zone group. In some embodiments, each playback zone or zone group may be associated with a playback queue containing information corresponding to zero or more audio items for playback by the playback zone or zone group. For instance, each audio item in the playback queue may comprise a uniform resource identifier (URI), a uniform resource locator (URL) or some other identifier that may be used by a playback device in the playback zone or zone group to find and/or retrieve the audio item from a local audio content source or a networked audio content source, possibly for playback by the playback device. 
     In one example, a playlist may be added to a playback queue, in which case information corresponding to each audio item in the playlist may be added to the playback queue. In another example, audio items in a playback queue may be saved as a playlist. In a further example, a playback queue may be empty, or populated but “not in use” when the playback zone or zone group is playing continuously streaming audio content, such as Internet radio that may continue to play until otherwise stopped, rather than discrete audio items that have playback durations. In an alternative embodiment, a playback queue can include Internet radio and/or other streaming audio content items and be “in use” when the playback zone or zone group is playing those items. Other examples are also possible. 
     When playback zones or zone groups are “grouped” or “ungrouped,” playback queues associated with the affected playback zones or zone groups may be cleared or re-associated. For example, if a first playback zone including a first playback queue is grouped with a second playback zone including a second playback queue, the established zone group may have an associated playback queue that is initially empty, that contains audio items from the first playback queue (such as if the second playback zone was added to the first playback zone), that contains audio items from the second playback queue (such as if the first playback zone was added to the second playback zone), or a combination of audio items from both the first and second playback queues. Subsequently, if the established zone group is ungrouped, the resulting first playback zone may be re-associated with the previous first playback queue, or be associated with a new playback queue that is empty or contains audio items from the playback queue associated with the established zone group before the established zone group was ungrouped. Similarly, the resulting second playback zone may be re-associated with the previous second playback queue, or be associated with a new playback queue that is empty, or contains audio items from the playback queue associated with the established zone group before the established zone group was ungrouped. Other examples are also possible. 
     Referring back to the user interface  400  of  FIG.  4   , the graphical representations of audio content in the playback queue region  440  may include track titles, artist names, track lengths, and other relevant information associated with the audio content in the playback queue. In one example, graphical representations of audio content may be selectable to bring up additional selectable icons to manage and/or manipulate the playback queue and/or audio content represented in the playback queue. For instance, a represented audio content may be removed from the playback queue, moved to a different position within the playback queue, or selected to be played immediately, or after any currently playing audio content, among other possibilities. A playback queue associated with a playback zone or zone group may be stored in a memory on one or more playback devices in the playback zone or zone group, on a playback device that is not in the playback zone or zone group, and/or some other designated device. Playback of such a playback queue may involve one or more playback devices playing back media items of the queue, perhaps in sequential or random order. 
     The audio content sources region  450  may include graphical representations of selectable audio content sources from which audio content may be retrieved and played by the selected playback zone or zone group. Discussions pertaining to audio content sources may be found in the following section. 
       FIG.  5    depicts a smartphone  500  that includes one or more processors, a tangible computer-readable memory, a network interface, and a display. Smartphone  500  might be an example implementation of control device  126  or  128  of  FIG.  1   , or control device  300  of  FIG.  3   , or other control devices described herein. By way of example, reference will be made to smartphone  500  and certain control interfaces, prompts, and other graphical elements that smartphone  500  may display when operating as a control device of a media playback system (e.g., of media playback system  100 ). Within examples, such interfaces and elements may be displayed by any suitable control device, such as a smartphone, tablet computer, laptop or desktop computer, personal media player, or a remote control device. 
     While operating as a control device of a media playback system, smartphone  500  may display one or more controller interface, such as controller interface  400 . Similar to playback control region  410 , playback zone region  420 , playback status region  430 , playback queue region  440 , and/or audio content sources region  450  of  FIG.  4   , smartphone  500  might display one or more respective interfaces, such as a playback control interface, a playback zone interface, a playback status interface, a playback queue interface, and/or an audio content sources interface. Example control devices might display separate interfaces (rather than regions) where screen size is relatively limited, such as with smartphones or other handheld devices. 
     D. Example Audio Content Sources 
     As indicated previously, one or more playback devices in a zone or zone group may be configured to retrieve for playback audio content (e.g., according to a corresponding URI or URL for the audio content) from a variety of available audio content sources. In one example, audio content may be retrieved by a playback device directly from a corresponding audio content source (e.g., a line-in connection). In another example, audio content may be provided to a playback device over a network via one or more other playback devices or network devices. 
     Example audio content sources may include a memory of one or more playback devices in a media playback system such as the media playback system  100  of  FIG.  1   , local music libraries on one or more network devices (such as a control device, a network-enabled personal computer, or a networked-attached storage (NAS), for example), streaming audio services providing audio content via the Internet (e.g., the cloud), or audio sources connected to the media playback system via a line-in input connection on a playback device or network devise, among other possibilities. 
     In some embodiments, audio content sources may be regularly added or removed from a media playback system such as the media playback system  100  of  FIG.  1   . In one example, an indexing of audio items may be performed whenever one or more audio content sources are added, removed or updated. Indexing of audio items may involve scanning for identifiable audio items in all folders/directory shared over a network accessible by playback devices in the media playback system, and generating or updating an audio content database containing metadata (e.g., title, artist, album, track length, among others) and other associated information, such as a URI or URL for each identifiable audio item found. Other examples for managing and maintaining audio content sources may also be possible. 
     E. Example Calibration Sequence 
     One or more playback devices of a media playback system may output one or more calibration sounds as part of a calibration sequence or procedure. Such a calibration sequence may calibration the one or more playback devices to particular locations within a listening area. In some cases, the one or more playback devices may be joining into a grouping, such as a bonded zone or zone group. In such cases, the calibration procedure may calibrate the one or more playback devices as a group. 
     The one or more playback devices may initiate the calibration procedure based on a trigger condition. For instance, a recording device, such as control device  126  of media playback system  100 , may detect a trigger condition that causes the recording device to initiate calibration of one or more playback devices (e.g., one or more of playback devices  102 - 124 ). Alternatively, a playback device of a media playback system may detect such a trigger condition (and then perhaps relay an indication of that trigger condition to the recording device). 
     In some embodiments, detecting the trigger condition may involve detecting input data indicating a selection of a selectable control. For instance, a recording device, such as control device  126 , may display an interface (e.g., control interface  400  of  FIG.  4   ), which includes one or more controls that, when selected, initiate calibration of a playback device, or a group of playback devices (e.g., a zone). 
     To illustrate such a control,  FIG.  6    shows smartphone  500  which is displaying an example control interface  600 . Control interface  600  includes a graphical region  602  that prompts to tap selectable control  604  (Start) when ready. When selected, selectable control  604  may initiate the calibration procedure. As shown, selectable control  604  is a button control. While a button control is shown by way of example, other types of controls are contemplated as well. 
     Control interface  600  further includes a graphical region  606  that includes a video depicting how to assist in the calibration procedure. Some calibration procedures may involve moving a microphone through an environment in order to obtain samples of the calibration sound at multiple physical locations. In order to prompt a user to move the microphone, the control device may display a video or animation depicting the step or steps to be performed during the calibration. 
     To illustrate movement of the control device during calibration,  FIG.  7    shows media playback system  100  of  FIG.  1   .  FIG.  7    shows a path  700  along which a recording device (e.g., control device  126 ) might be moved during calibration. As noted above, the recording device may indicate how to perform such a movement in various ways, such as by way of a video or animation, among other examples. A recording device might detect iterations of a calibration sound emitted by one or more playback devices of media playback system  100  at different points along the path  700 , which may facilitate a space-averaged calibration of those playback devices. 
     In other examples, detecting the trigger condition may involve a playback device detecting that the playback device has become uncalibrated, which might be caused by moving the playback device to a different position. For example, the playback device may detect physical movement via one or more sensors that are sensitive to movement (e.g., an accelerometer). As another example, the playback device may detect that it has been moved to a different zone (e.g., from a “Kitchen” zone to a “Living Room” zone), perhaps by receiving an instruction from a control device that causes the playback device to leave a first zone and join a second zone. 
     In further examples, detecting the trigger condition may involve a recording device (e.g., a control device or playback device) detecting a new playback device in the system. Such a playback device may have not yet been calibrated for the environment. For instance, a recording device may detect a new playback device as part of a set-up procedure for a media playback system (e.g., a procedure to configure one or more playback devices into a media playback system). In other cases, the recording device may detect a new playback device by detecting input data indicating a request to configure the media playback system (e.g., a request to configure a media playback system with an additional playback device). 
     In some cases, the first recording device (or another device) may instruct the one or more playback devices to emit the calibration sound. For instance, a recording device, such as control device  126  of media playback system  100 , may send a command that causes a playback device (e.g., one of playback devices  102 - 124 ) to emit a calibration sound. The control device may send the command via a network interface (e.g., a wired or wireless network interface). A playback device may receive such a command, perhaps via a network interface, and responsively emit the calibration sound. 
     In some embodiments, the one or more playback devices may repeatedly emit the calibration sound during the calibration procedure such that the calibration sound covers the calibration frequency range during each repetition. With a moving microphone, repetitions of the calibration sound are detected at different physical locations within the environment, thereby providing samples that are spaced throughout the environment. In some cases, the calibration sound may be periodic calibration signal in which each period covers the calibration frequency range. 
     To facilitate determining a frequency response, the calibration sound should be emitted with sufficient energy at each frequency to overcome background noise. To increase the energy at a given frequency, a tone at that frequency may be emitted for a longer duration. However, by lengthening the period of the calibration sound, the spatial resolution of the calibration procedure is decreased, as the moving microphone moves further during each period (assuming a relatively constant velocity). As another technique to increase the energy at a given frequency, a playback device may increase the intensity of the tone. However, in some cases, attempting to emit sufficient energy in a short amount of time may damage speaker drivers of the playback device. 
     Some implementations may balance these considerations by instructing the playback device to emit a calibration sound having a period that is approximately ⅜th of a second in duration (e.g., in the range of ¼ to 1 second in duration). In other words, the calibration sound may repeat at a frequency of 2-4 Hz. Such a duration may be long enough to provide a tone of sufficient energy at each frequency to overcome background noise in a typical environment (e.g., a quiet room) but also be short enough that spatial resolution is kept in an acceptable range (e.g., less than a few feet assuming normal walking speed). 
     In some embodiments, the one or more playback devices may emit a hybrid calibration sound that combines a first component and a second component having respective waveforms. For instance, an example hybrid calibration sound might include a first component that includes noises at certain frequencies and a second component that sweeps through other frequencies (e.g., a swept-sine). A noise component may cover relatively low frequencies of the calibration frequency range (e.g., 10-50 Hz) while the swept signal component covers higher frequencies of that range (e.g., above 50 Hz). Such a hybrid calibration sound may combine the advantages of its component signals. 
     A swept signal (e.g., a chirp or swept sine) is a waveform in which the frequency increases or decreases with time. Including such a waveform as a component of a hybrid calibration sound may facilitate covering a calibration frequency range, as a swept signal can be chosen that increases or decreases through the calibration frequency range (or a portion thereof). For example, a chirp emits each frequency within the chirp for a relatively short time period such that a chirp can more efficiently cover a calibration range relative to some other waveforms.  FIG.  8    shows a graph  800  that illustrates an example chirp. As shown in  FIG.  8   , the frequency of the waveform increases over time (plotted on the X-axis) and a tone is emitted at each frequency for a relatively short period of time. 
     However, because each frequency within the chirp is emitted for a relatively short duration of time, the amplitude (or sound intensity) of the chirp must be relatively high at low frequencies to overcome typical background noise. Some speakers might not be capable of outputting such high intensity tones without risking damage. Further, such high intensity tones might be unpleasant to humans within audible range of the playback device, as might be expected during a calibration procedure that involves a moving microphone. Accordingly, some embodiments of the calibration sound might not include a chirp that extends to relatively low frequencies (e.g., below 50 Hz). Instead, the chirp or swept signal may cover frequencies between a relatively low threshold frequency (e.g., a frequency around 50-100 Hz) and a maximum of the calibration frequency range. The maximum of the calibration range may correspond to the physical capabilities of the channel(s) emitting the calibration sound, which might be 20,000 Hz or above. 
     A swept signal might also facilitate the reversal of phase distortion caused by the moving microphone. As noted above, a moving microphone causes phase distortion, which may interfere with determining a frequency response from a detected calibration sound. However, with a swept signal, the phase of each frequency is predictable (as Doppler shift). This predictability facilitates reversing the phase distortion so that a detected calibration sound can be correlated to an emitted calibration sound during analysis. Such a correlation can be used to determine the effect of the environment on the calibration sound. 
     As noted above, a swept signal may increase or decrease frequency over time. In some embodiments, the recording device may instruct the one or more playback devices to emit a chirp that descends from the maximum of the calibration range (or above) to the threshold frequency (or below). A descending chirp may be more pleasant to hear to some listeners than an ascending chirp, due to the physical shape of the human ear canal. While some implementations may use a descending swept signal, an ascending swept signal may also be effective for calibration. 
     As noted above, example calibration sounds may include a noise component in addition to a swept signal component. Noise refers to a random signal, which is in some cases filtered to have equal energy per octave. In embodiments where the noise component is periodic, the noise component of a hybrid calibration sound might be considered to be pseudorandom. The noise component of the calibration sound may be emitted for substantially the entire period or repetition of the calibration sound. This causes each frequency covered by the noise component to be emitted for a longer duration, which decreases the signal intensity typically required to overcome background noise. 
     Moreover, the noise component may cover a smaller frequency range than the chirp component, which may increase the sound energy at each frequency within the range. As noted above, a noise component might cover frequencies between a minimum of the frequency range and a threshold frequency, which might be, for example around a frequency around 50-100 Hz. As with the maximum of the calibration range, the minimum of the calibration range may correspond to the physical capabilities of the channel(s) emitting the calibration sound, which might be 20 Hz or below. 
       FIG.  9    shows a graph  900  that illustrates an example brown noise. Brown noise is a type of noise that is based on Brownian motion. In some cases, the playback device may emit a calibration sound that includes a brown noise in its noise component. Brown noise has a “soft” quality, similar to a waterfall or heavy rainfall, which may be considered pleasant to some listeners. While some embodiments may implement a noise component using brown noise, other embodiments may implement the noise component using other types of noise, such as pink noise or white noise. As shown in  FIG.  9   , the intensity of the example brown noise decreases by 6 dB per octave (20 dB per decade). 
     Some implementations of a hybrid calibration sound may include a transition frequency range in which the noise component and the swept component overlap. As indicated above, in some examples, the control device may instruct the playback device to emit a calibration sound that includes a first component (e.g., a noise component) and a second component (e.g., a sweep signal component). The first component may include noise at frequencies between a minimum of the calibration frequency range and a first threshold frequency, and the second component may sweep through frequencies between a second threshold frequency and a maximum of the calibration frequency range. 
     To overlap these signals, the second threshold frequency may a lower frequency than the first threshold frequency. In such a configuration, the transition frequency range includes frequencies between the second threshold frequency and the first threshold frequency, which might be, for example, 50-100 Hz. By overlapping these components, the playback device may avoid emitting a possibly unpleasant sound associated with a harsh transition between the two types of sounds. 
       FIGS.  10 A and  10 B  illustrate components of example hybrid calibration signals that cover a calibration frequency range  1000 .  FIG.  10 A  illustrates a first component  1002 A (i.e., a noise component) and a second component  1004 A of an example calibration sound. Component  1002 A covers frequencies from a minimum  1008 A of the calibration range  1000  to a first threshold frequency  1008 A. Component  1004 A covers frequencies from a second threshold  1010 A to a maximum of the calibration frequency range  1000 . As shown, the threshold frequency  1008 A and the threshold frequency  1010 A are the same frequency. 
       FIG.  10 B  illustrates a first component  1002 B (i.e., a noise component) and a second component  1004 B of another example calibration sound. Component  1002 B covers frequencies from a minimum  1008 B of the calibration range  1000  to a first threshold frequency  1008 A. Component  1004 A covers frequencies from a second threshold  1010 B to a maximum  1012 B of the calibration frequency range  1000 . As shown, the threshold frequency  1010 B is a lower frequency than threshold frequency  1008 B such that component  1002 B and component  1004 B overlap in a transition frequency range that extends from threshold frequency  1010 B to threshold frequency  1008 B. 
       FIG.  11    illustrates one example iteration (e.g., a period or cycle) of an example hybrid calibration sound that is represented as a frame  1100 . The frame  1100  includes a swept signal component  1102  and noise component  1104 . The swept signal component  1102  is shown as a downward sloping line to illustrate a swept signal that descends through frequencies of the calibration range. The noise component  1104  is shown as a region to illustrate low-frequency noise throughout the frame  1100 . As shown, the swept signal component  1102  and the noise component overlap in a transition frequency range. The period  1106  of the calibration sound is approximately ⅜ths of a second (e.g., in a range of ¼ to ½ second), which in some implementation is sufficient time to cover the calibration frequency range of a single channel. 
       FIG.  12    illustrates an example periodic calibration sound  1200 . Five iterations (e.g., periods) of hybrid calibration sound  1100  are represented as a frames  1202 ,  1204 ,  1206 ,  1208 , and  1210 . In each iteration, or frame, the periodic calibration sound  1200  covers a calibration frequency range using two components (e.g., a noise component and a swept signal component). 
     In some embodiments, a spectral adjustment may be applied to the calibration sound to give the calibration sound a desired shape, or roll off, which may avoid overloading speaker drivers. For instance, the calibration sound may be filtered to roll off at 3 dB per octave, or 1/f. Such a spectral adjustment might not be applied to vary low frequencies to prevent overloading the speaker drivers. 
     In some embodiments, the calibration sound may be pre-generated. Such a pre-generated calibration sound might be stored on the control device, the playback device, or on a server (e.g., a server that provides a cloud service to the media playback system). In some cases, the control device or server may send the pre-generated calibration sound to the playback device via a network interface, which the playback device may retrieve via a network interface of its own. Alternatively, a control device may send the playback device an indication of a source of the calibration sound (e.g., a URI), which the playback device may use to obtain the calibration sound. 
     Alternatively, the control device or the playback device may generate the calibration sound. For instance, for a given calibration range, the control device may generate noise that covers at least frequencies between a minimum of the calibration frequency range and a first threshold frequency and a swept sine that covers at least frequencies between a second threshold frequency and a maximum of the calibration frequency range. The control device may combine the swept sine and the noise into the periodic calibration sound by applying a crossover filter function. The cross-over filter function may combine a portion of the generated noise that includes frequencies below the first threshold frequency and a portion of the generated swept sine that includes frequencies above the second threshold frequency to obtain the desired calibration sound. The device generating the calibration sound may have an analog circuit and/or digital signal processor to generate and/or combine the components of the hybrid calibration sound. 
     Further example calibration procedures are described in U.S. Pat. Application No. 14/805,140 filed Jul. 21, 2015, entitled “Hybrid Test Tone For Space-Averaged Room Audio Calibration Using A Moving Microphone,” U.S. Pat. Application No. 14/805,340 filed Jul. 21, 2015, entitled “Concurrent Multi-Loudspeaker Calibration with a Single Measurement,” and U.S. Pat. Application No. 14/864,393 filed Sep. 24, 2015, entitled “Facilitating Calibration of an Audio Playback Device,” which are incorporated herein in their entirety. 
     Calibration may be facilitated via one or more control interfaces, as displayed by one or more devices. Example interfaces are described in U.S. Pat. Application No. 14/696,014 filed Apr. 24, 2015, entitled “Speaker Calibration,” and U.S. Pat. Application No. 14/826,873 filed Aug. 14, 2015, entitled “Speaker Calibration User Interface,” which are incorporated herein in their entirety. 
     Moving now to several example implementations, implementations  1300 ,  1500  and  1600  shown in  FIGS.  13 ,  15  and  16   , respectively present example embodiments of techniques described herein. These example embodiments that can be implemented within an operating environment including, for example, the media playback system  100  of  FIG.  1   , one or more of the playback device  200  of  FIG.  2   , or one or more of the control device  300  of  FIG.  3   , as well as other devices described herein and/or other suitable devices. Further, operations illustrated by way of example as being performed by a media playback system can be performed by any suitable device, such as a playback device or a control device of a media playback system. Implementations  1300 ,  1500  and  1600  may include one or more operations, functions, or actions as illustrated by one or more of blocks shown in  FIGS.  13 ,  15  and  16   . Although the blocks are illustrated in sequential order, these blocks may also be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. 
     In addition, for the implementations disclosed herein, the flowcharts show functionality and operation of one possible implementation of present embodiments. In this regard, each block may represent a module, a segment, or a portion of program code, which includes one or more instructions executable by a processor for implementing specific logical functions or steps in the process. The program code may be stored on any type of computer readable medium, for example, such as a storage device including a disk or hard drive. The computer readable medium may include non-transitory computer readable medium, for example, such as computer-readable media that stores data for short periods of time like register memory, processor cache, and Random Access Memory (RAM). The computer readable medium may also include non-transitory media, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. The computer readable medium may be considered a computer readable storage medium, for example, or a tangible storage device. In addition, for the implementations disclosed herein, each block may represent circuitry that is wired to perform the specific logical functions in the process. 
     III. Example Techniques to Facilitate Calibration 
     As discussed above, embodiments described herein may facilitate the calibration of one or more playback devices by determining multiple calibrations.  FIG.  13    illustrates an example implementation  1300  by which a media playback system determines a first and second calibration. One of the two calibrations may be applied to playback by one or more playback devices of the media playback system. 
     A. Detect Calibration Sounds As Emitted By Playback Device(s) 
     At block  1302 , implementation  1300  involves detecting one or more calibration sounds as emitted by one or more playback devices during a calibration sequence. For instance, a recording device (e.g., control device  126  or  128  of  FIG.  1   ) may detect one or more calibration sounds as emitted by playback devices of a media playback system (e.g., media playback system  100 ) via a microphone. In practice, some of the calibration sound may be attenuated or drowned out by the environment or by other conditions, which may interfere with the recording device detecting all of the calibration sound. As such, the recording device may measure a portion of the calibration sounds as emitted by playback devices of a media playback system. The calibration sound(s) may be any of the example calibration sounds described above with respect to the example calibration procedure, as well as any suitable calibration sound. 
     Given that the recording device is moving throughout the calibration environment, the recording device may detect iterations of the calibration sound at different physical locations of the environment, which may provide a better understanding of the environment as a whole. For example, referring back to  FIG.  7   , control device  126  of media playback system  100  may detect calibration sounds emitted by one or more playback devices (e.g., playback devices  104 ,  106 ,  108 , and/or  110  of the Living Room Zone) at various points along the path  700  (e.g., at point  702  and/or point  704 ). Alternatively, the control device may record the calibration signal along the path. 
     As noted above, in some embodiment, a playback device may output a periodic calibration sound (or perhaps repeat the same calibration sound) such that the playback device measures a repetition of the calibration sound at different points along the paths. Each recorded repetition may be referred to as a frame. Different frames may represent responses of the environment to the calibration sound at various physical locations within the environment. Comparison of such frames may indicate how the acoustic characteristics change from one physical location in the environment to another, which influences the calibration determined for the playback device in that environment. 
     In some implementations, a recording device may measure one or more first samples (e.g., first frames) while in motion through a given environment. In some implementations, the first samples may indicate responses of the given environment to the calibration sound at a plurality of locations throughout the environment. In combination, such responses may indicate response of the environment generally. Such responses may ultimately be used in determining a first calibration for the one or more playback devices (e.g., a spectral calibration). 
     Further, a recording device may measure one or more second samples (e.g., second frames) while stationary at one or more particular locations within the given environment. The second samples may indicate responses of the given environment to the calibration sound at the one or more particular locations. Such locations may correspond to preferred listening locations (e.g., a favorite chair or other seated or standing location). Frames measured at such locations may represent respective response of the environment to the calibration sound as detected in those locations. A given listening location may cover a certain area (e.g., a sofa may cover a portion of a living room). As such, while measuring a response of such an location, remaining stationary while measuring samples at that location may involve some movement generally within a certain area associated with the location. 
     Such responses may ultimately be used in determining a second calibration for the one or more playback devices (e.g., a spatial calibration), which may configure output from the one or more speakers to those locations. In some cases, a recording device may measure multiple samples or frames at a particular location. These samples may be combined (e.g., averaged) to determine a response for that particular location. 
     While the recording device is detecting the one or more calibration sounds, movement of that recording device through the listening area may be detected. Such movement may be detected using a variety of sensors and techniques. For instance, the first recording device may receive movement data from a sensor, such as an accelerometer, GPS, or inertial measurement unit. In other examples, a playback device may facilitate the movement detection. For example, given that a playback device is stationary, movement of the recording device may be determined by analyzing changes in sound propagation delay between the recording device and the playback device. 
     Based on such detected movement, the recording device may identify first samples (e.g., frames) that were measured while the recording device was in motion and second samples that were measured while the recording device was stationary. For instance, if the movement data indicates that the recording device is stationary for a threshold period of time (e.g., more than a few seconds or so), the recording device may identify that location as a particular location (e.g., a preferred listening location) and further identify samples (e.g. frames) received at that location as corresponding to that location. Such samples may be used by a processing device to determine a calibration associated with the particular locations (e.g., a spatial calibration associated with preferred listening locations). Samples measured while the movement data indicates that the recording device is moving may be identified as first samples. These samples may be used by a processing device to determine a calibration associated with the environment generally (e.g., a spectral calibration). 
     In some embodiments, measuring the second samples at the one or more particular locations may include measuring distance from two or more playback devices to the one or more particular locations. For instance, a given zone under calibration may include a plurality of devices (e.g., playback devices  104 ,  106 ,  108 , and/or  110  of the Living Room Zone). In operation, such devices may output audio jointly (e.g., in synchrony, or as respective channels of an audio content, such as stereo or surround sound content). Measure such distances may involve measuring respective propagation delays of sound from the playback devices to the recording device. Synchronization features of the playback devices described herein may facilitate such measurement, as sound emitted from the playback devices may be approximately simultaneous. 
     Using measured distances from such playback devices to a given location, a calibration can be determined to offset differences in the measured distances. For instance, a calibration may time output of audio by the respective playback devices to offset differences in the propagation delays of the respective playback devices. Such calibration may facilitate sound from two or more of the playback devices propagating to a particular location at around the same time. Yet further, such measured distances may be used to calibrate the two or more playback devices to different loudness such that a listener at the preferred location might perceive audio from the two or more to be approximately the same loudness. Other examples are possible as well. 
     Although some example calibration procedures contemplated herein suggest movement by the recording devices, such movement is not necessary. For instance, in an example calibration sequence, a first recording device may move through the environment while measuring moving frames (e.g., first frames) while a second recording device remains stationary at a preferred location. In other examples, each recording device may move and pause at one or more particular locations. Other combinations are possible as well. 
     B. Determine Calibrations 
     In  FIG.  13   , at block  1304 , implementation  1300  involves determining two or more calibrations. For instance, a processing device may determine a first calibration and a second calibration (and possibly additional calibrations as well) for the one or more playback devices. In some cases, when applied to playback by the one or more playback devices, a given calibration may offset acoustics characteristics of the environment to achieve a given response (e.g., a flat response). For instance, if a given environment attenuates frequencies around 500 Hz and amplifies frequencies around 14000 Hz, a calibration might boost frequencies around 500 Hz and cut frequencies around 14000 Hz so as to offset these environmental effects. 
     Some example techniques for determining a calibration are described in U.S. Pat. Application No. 13/536,493 filed Jun. 28, 2012, entitled “System and Method for Device Playback Calibration” and published as US 2014/0003625 A1, which is incorporated herein in its entirety. Example techniques are described in paragraphs [0019]-[0025] and [0068]-[0118] as well as generally throughout the specification. 
     Further example techniques for determining a calibration are described in U.S. Pat. Application No. 14/216,306 filed Mar. 17, 2014, entitled “Audio Settings Based On Environment” and published as US 2015/0263692 A1, which is incorporated herein in its entirety. Example techniques are described in paragraphs [0014]-[0025] and [0063]-[0114] as well as generally throughout the specification. 
     Additional example techniques for determining a calibration are described in U.S. Pat. Application No. 14/481,511 filed Sep. 9, 2014, entitled “Playback Device Calibration” and published as US 2016/0014534 A1, which is incorporated herein in its entirety. Example techniques are described in paragraphs [0017]-[0043] and [0082]-[0184] as well as generally throughout the specification. 
     The processing device may be implemented in various devices. In some cases, the processing device may be a control device or a playback device of the media playback system. Such a device may operate also as a recording device, such that the processing device and the recording device are the same device. Alternatively, the processing device may be a server (e.g., a server that is providing a cloud service to the media playback system via the Internet). Other examples are possible as well. 
     In some implementations, the processing device may determine a first calibration based on at least the first samples of the one or more calibrations sounds. As noted above, such first samples may represent respective responses of the given environment to the calibration sound at a plurality of locations throughout the environment. In combination, such responses may indicate response of the environment generally and may ultimately be used in determining a first calibration for the one or more playback devices. For instance, the processing device may determine a spectral calibration that offsets acoustics characteristics of the environment as indicated by the response(s), perhaps by boosting or cutting output at various frequencies to offset attenuation or amplification by the environment. 
     To illustrate, continuing the example above, control device  126  may determine a first calibration for the Living Room zone of media playback system  100 , which includes playback devices  104 ,  106 ,  108 , and  110 . The shape of the Living Room, the open layout leading to the Kitchen and Dining Rooms, the furniture within such rooms, and other environmental factors may give the Living Room certain acoustic characteristics (e.g., by attenuating or amplifying certain frequencies). An example first calibration may be based on samples measured by control device  126  while moving through this room (e.g., along path  700 ). When applied to playback by this zone, the first calibration may offset some of these acoustic characteristics by boosting or cutting frequencies affected by the environment). 
     The processing device may determine a second calibration based on at least the second samples of the one or more calibrations sounds. As noted above, such samples may indicate responses of the given environment to the calibration sound at the one or more particular locations. Frames measured at such locations may represent respective response of the environment to the calibration sound as detected in those locations. 
     Based on such responses, the second calibration may determine a calibration that adjusts output of the playback devices spectrally (e.g., a spectral calibration). Such a calibration may use the first samples and/or the second samples. In some cases, the second samples may be weighted more heavily in the calibration than the first samples, so as to offset acoustics characteristics of the environment as detected in the particular location(s). In some cases, the second samples may be weighted more heavily by virtue of these samples being more numerous (as multiple samples are measured while the recording device is stationary), which may cause a combined response to weigh towards these locations. Alternatively, the particular locations might be emphasized in the spectral calibration more explicitly, or not at all. 
     The second calibration may also calibrate the one or more playback devices spatially. For instance, the second calibration may offset differences in the measured distances from such playback devices to the particular location(s) that correspond to the second samples. For instance, as noted above, a calibration may time output of audio by the respective playback devices to offset differences in the propagation delays of the respective playback devices. Such calibration may facilitate sound from two or more of the playback devices propagating to a particular location at around the same time. 
     Yet further, such measured distances may be used to calibrate the two or more playback devices to different gains. For instance, the second calibration may adjust respective gain of the one or more playback devices to offset differences such that a listener at the preferred location might perceive audio from the two or more to be approximately the same loudness. As noted above, two or more playback devices may be joined into a bonded zone or other grouping. For instance, two playback devices may be joined into a stereo pair. A second calibration for such a stereo pair may balance gain of the stereo pair to the one or more particular locations. Other examples are possible as well. 
     To illustrate, continuing the example above, control device  126  may determine a second calibration for the Living Room zone of media playback system  100 , perhaps in addition to the first calibration for that zone described above. An example second calibration may be based on samples measured while stationary at one or more particular locations in this room (e.g., at point  704 ) and perhaps also on other samples measured while moving through this room (e.g., along path  700 ). When applied to playback by this zone, the second calibration may calibrate the Living Room zone spectrally, perhaps by offsetting acoustic characteristics of the room. Alternatively, or additionally, the second calibration may calibrate the Living Room zone spatially, perhaps by offsetting differences in respective distances between playback devices  104 ,  106 ,  108 , and/or  110  and the one or more particular locations in this room (e.g., at point  704 ). 
     C. Apply a Calibration to Playback 
     At block  1306 , implementation  1300  involves applying a calibration to playback. For instance, a recording device (e.g., a control device) may send one or more messages that instructs the one or more playback devices to apply a particular one of two or more calibrations to playback. Such messages may also include the determined calibration, which may be stored and/or maintained on the playback device(s) or a device that is communicatively coupled to the playback device(s). Alternatively, each of the one or more playback devices may identify a particular calibration to apply, perhaps based on a use case. Yet further, a playback device acting as a group coordinator for a group of playback devices (e.g., a zone group or bonded zone) may identify a particular calibration to apply to playback by the group of playback devices. In operation, when playing back media, the applied calibration may adjust output of the playback devices. 
     As noted above, playback devices undergoing calibration may be a member of a zone (e.g., the zones of media playback system  100 ). Further, such playback devices may be joined into a grouping, such as a bonded zone or zone group, and may undergo calibration as the grouping. In such embodiments, applying a calibration may be involve applying a calibration to a zone, a zone group, a bonded zone, or other configuration into which the playback devices are arranged. Further, a given calibration may include respective calibrations for multiple playback devices, perhaps adjusted for the types or capabilities of the playback device. Yet further, as noted above, individual calibrations may adjust for respective physical locations of the playback devices. 
     In some implementations, the media playback system may apply a particular one of the calibrations (e.g., a first or second calibration) based on one or more operating conditions, which may be indicative of different use cases. For instance, a control device may detect that a certain change has occurred such that a particular condition is present and then instruct the playback device(s) to apply a certain calibration corresponding to that particular condition. Alternatively, a playback device may detect the condition and apply a particular calibration that corresponds to that condition. Yet further, a group coordinator may detect a condition (or receive a message indicating that such a condition is present) and apply a particular condition to playback by the group. 
     In some examples, the media playback system may apply a certain calibration based on the audio content being played back (or that has been instructed to be played back) by the one or more playback devices. For instance, the media playback system may detect that the one or more playback devices are playing back media content that consists of only audio (e.g., music). In such cases, the media playback system may apply a particular calibration, such as a spectral calibration (e.g., the first calibration described above). Such a calibration may tune playback across an environment generally (e.g., throughout the Living Room zone). 
     In some configurations, the one or more playback devices may receive media content that is associated with both audio and video (e.g., a television show or movie). The playback device(s) may play back the audio portion of the content while a television or monitor plays back the video portion. When playing back such content, the media playback system may apply a particular calibration. In some cases, the media playback system may apply a spatial calibration (e.g., the second calibration described above), as such a calibration may configure playback to one or more particular locations (e.g., a seating location within the Living Room zone of media playback system  100 , which may be used to watch and listen to the media content). 
     The media playback system may apply a certain calibration based on the source of the audio content. For instance, some playback devices may receive content via a network interface (e.g., streaming music) or via one or more physical inputs (e.g., analog line-in input or a digital input such as TOS-LINK® or HDMI@). Receiving content via a particular one of these sources may suggest a particular use case. For instance, receiving content via the network interface may indicate music playback. As such, while receiving content via the network interface, the media playback system may apply a particular calibration (e.g., the first calibration). As another example, receiving content via a particular physical input may indicate home theater use (i.e., playback of audio from a television show or movie). While playing back content from that input, the media playback system may apply a different calibration (e.g., the second calibration). 
     As noted above, playback devices may be joined into various groupings, such as a zone group or bonded zone. In some implementations, upon two or more playback devices being joined into a grouping, the two or more playback devices may apply a particular calibration. For instance, a zone group of two or more zones may configure the playback devices of those zones to playback media in synchrony (e.g., to playback music across multiple zones). Based on detecting that the zone group was formed, the media playback system may apply a certain calibration associated with zone groups (or the particular zone group that was formed). This might be a spectral calibration so as to tune playback across the multiple zones generally. 
     In some example media playback systems, one or more of the zones may be configured to operate in one or more “zone scenes.” Zone scenes may cause one or more zones to play particular content at a particular time of day. For instance, a particular zone scene configured for the Kitchen zone of media playback system  100  might cause playback device  114  to playback a particular internet radio station (e.g., a news station) during breakfast (e.g., from 7:00 AM to 7:30 AM). Another example zone scene may cause the Living Room zone and the Dining Room zone to form a zone group to play a particular playlist at 6:00 PM (e.g., when the user typically arrives home from school or work). Further example zone scenes and techniques involving such scenes are described in U.S. Pat. Application No. 11/853,790 filed Sep. 11, 2007, entitled “Controlling and manipulating groupings in a multi-zone media system,” which is incorporated herein in its entirety. 
     A given zone scene may be associated with a particular calibration. For instance, upon entering a particular zone scene, the media playback system may apply a particular calibration associated with that zone scene to playback by the one or more playback devices. Alternatively, the content or configuration associated with a zone scene may cause the playback devices to apply a particular calibration. For example, a zone scene may involve playback of a particular media content or content source that causes the playback devices to apply a particular calibration. 
     In further examples, a media playback system may detect the presence and/or location of listeners in proximity to the one or more playback devices (e.g., within a zone). Such listeners may be detected using various techniques. For instance, Wi-Fi or other wireless signals from personal devices (e.g., smartphones or tablets) carried by the listeners may be detected by wireless receivers on the playback devices. Alternatively, voices may be detected by microphones on one or more devices of the media playback systems. As another example, the playback devices may detect movement of listeners near the playback devices via proximity sensors. Other examples are possible as well. 
     The media playback devices may apply a certain calibration based on the presence and/or location of listeners relative to the to the one or more playback devices. For instance, if there are multiple listeners in a room (e.g., in proximity to the playback devices of a zone), the media playback system may apply a particular calibration (e.g., the first calibration, so as to tune playback generally across the zone). However, if the listeners are clustered near the one or more particular locations, the media playback system may apply a different calibration (e.g., the second calibration, so as to configure playback to those locations). 
     In yet further examples, a control device of the media playback system may display a control interface by which a particular calibration can be selected. To illustrate such an interface,  FIG.  14    shows smartphone  500  which is displaying an example control interface  1400 . Control interface  1400  includes a graphical region  1402  that include a prompt to select a calibration for the Living Room zone of media playback system  100 . Smartphone  500  may detect input indicating a selection of selectable control  1402  or  1406 .. Selection of selectable control  1404  may indicate an instruction apply a first calibration to the Living Room zone. Similarly, selection of selectable control  1406  may indicate an instruction apply a second calibration to the Living Room zone. 
     In some examples, the calibration or calibration state may be shared among devices of a media playback system using one or more state variables. Some examples techniques involving calibration state variables are described in U.S. Pat. Application No. 14/793,190 filed Jul. 7, 2015, entitled “Calibration State Variable,” and U.S. Pat. Application No. 14/793,205 filed Jul. 7, 2015, entitled “Calibration Indicator,” which are incorporated herein in their entirety. 
     IV. Example Techniques to Apply a Calibration 
     As discussed above, embodiments described herein may involve applying one of multiple calibrations to playback by a media playback system.  FIG.  15    illustrates an example implementation  1500  by which a playback device detects a particular playback state and applies a calibration corresponding to that playback state. 
     A. Receive Calibrations 
     At block  1502 , implementation  1500  involves receiving two or more calibrations. For instance, a playback device may receive two or more calibrations (e.g., the first and second calibrations described above in connection with implementation  1300  of  FIG.  13   ) via a network interface from a processing device. Such calibration may have been determined by way of a calibration sequence, such as the example calibration sequences described above. The playback device may maintain these calibrations in data storage, perhaps as one or calibration curves (e.g., as the coefficients of a bi-quad filter). Alternatively, such calibrations may be maintained on a device or system that is communicatively coupled to the playback device via a network. The playback device may receive the calibrations from this device or system, perhaps upon request from the playback device when applying a given calibration. 
     B. Detect Playback State 
     At block  1504 , implementation  1500  involves detecting a playback state. For instance, the playback device may detect that it is playing back media content in a given playback state. Alternatively, the playback device may detect that it has been instructed to play back media content in a given playback state. Other examples are possible as well. 
     As described above, in some implementations, a particular may apply a particular one of the calibrations (e.g., a first or second calibration) based on one or more operating conditions, as described above in connection with block  1306  of implementation  1300 . Such operating conditions may correspond to various playback states. 
     In some examples, the playback device may apply a certain calibration based on the audio content that the playback device is playing back (or that it has been instructed to play back). For instance, the playback device may detect that it is playing back media content that consists of only audio (e.g., music). In such cases, the playback device may apply a particular calibration, such as a spectral calibration (e.g., the first calibration described above). Such a calibration may tune playback across an environment generally (e.g., throughout the Living Room zone). 
     In some configurations, the playback device may receive media content that is associated with both audio and video (e.g., a television show or movie). When playing back such content, the playback device may apply a particular calibration. In some cases, the playback device may apply a spatial calibration (e.g., the second calibration described above), as such a calibration may configure playback to one or more particular locations (e.g., a seating location within the Living Room zone of media playback system  100 , which may be used to watch and listen to the media content). 
     The playback device may apply a certain calibration based on the source of the audio content. Receiving content via a particular one of these sources may apply a particular use case. For instance, receiving content via a network interface may indicate music playback. As such, while receiving content via the network interface, the playback device may apply a particular calibration (e.g., the first calibration). As another example, receiving content via a particular physical input may indicate home theater use (i.e., playback of audio from a television show or movie). While playing back content from that input, the playback device may apply a different calibration (e.g., the second calibration). 
     As noted above, playback devices may be joined into various groupings, such as a zone group or bonded zone. In some implementations, upon being joined into a grouping with another playback device, the playback device may apply a particular calibration. For instance, based on detecting that the playback device has joined a particular zone group, the playback device may apply a certain calibration associated with zone groups (or with the particular zone group). This might be a spectral calibration so as to tune playback across the multiple zones generally. 
     As noted above, a given zone scene may be associated with a particular calibration. Upon entering a particular zone scene, the playback device may apply a particular calibration associated with that zone scene. Alternatively, the content or configuration associated with a zone scene may cause the playback device to apply a particular calibration. For example, a zone scene may involve playback of a particular media content or content source, which causes the playback device to apply a particular calibration. 
     As indicated above, a playback device may detect the presence and/or location of listeners in proximity to the one or more playback devices (e.g., within a zone). The playback device may apply a certain calibration based on the presence and/or location of listeners relative to the playback device. For instance, if there are multiple listeners in a room (e.g., in proximity to the playback devices of a zone), the playback device may apply a particular calibration (e.g., the first calibration, so as to configure playback generally across the zone). However, if the listeners are clustered near the one or more particular locations, the playback device may apply a different calibration (e.g., the second calibration, so as to configure playback to those locations). 
     In yet further examples, the playback state may be indicated to the playback device by way of one or more messages from a control device or another playback device. For instance, after receiving input that selects a particular calibration (e.g., via control interface  1400 ), a smartphone  500  may indicate to the playback device that a particular calibration is selected. The playback device may apply that calibration to playback. As another example, the playback device may be a member of a group, such as a bonded zone group. Another playback device, such as a group coordinator device of that group, may detect a playback state for the group and send a message indicating that playback state (or the calibration for that state) to the playback device. 
     C. Apply A Calibration 
     Referring again to  FIG.  15   , at block  1506 , implementation  1500  involves applying a calibration. For instance, as described above, a playback device may apply a calibration to playback by the playback device. In operation, when playing back media, the calibration may adjust output of the playback device, perhaps to configure the playback device to its operating environment. The particular calibration applied by the playback device may be one of a plurality of calibrations that the playback device maintains or has access to, such as the first and second calibrations noted above. 
     In some cases, the playback device may also apply the calibration to one or more additional playback devices. For instance, the playback device may be a member (e.g,. the group coordinator) of a group (e.g., a zone group). The playback device may send messages instructing other playback devices in the group to apply the calibration. Upon receiving such a message, these playback devices may apply the calibration. 
     V. Example Techniques To Facilitate Calibration Using A Recording Device 
     As noted above, embodiments described herein may facilitate the calibration of one or more playback devices.  FIG.  16    illustrates an example implementation  1600  by which recording device (e.g., a control device) facilitates calibration of one or more playback devices. 
     A. Display Prompt(s) for Calibration Sequence 
     At block  1602 , implementation  1600  involves displaying one or more prompts for a calibration sequence. Such prompts may serve as a guide through various aspects of a calibration sequence. For instance, such prompts may guide preparation of one or more playback devices to be calibrated, a recording device that will measure calibration sounds emitted by the one or more playback devices, and/or the environment in which the calibration will be carried out. 
     As noted above, example calibration sequences may involve a recording device moving through the environment so as to measure the calibration sounds at different locations. As such, example prompts displayed for a calibration sequence may include one or more prompts to move the control device. Such prompts may guide a user in moving the recording device during the calibration. 
     To illustrate, in  FIG.  17   , smartphone  500  is displaying control interface  1700  which includes graphical regions  1702  and  1704 . Graphical region  1702  prompts to watch an animation in graphical region  1704 . Such an animation may depict an example of how to move the smartphone within the environment during calibration to measure the calibration sounds at different locations. While an animation is shown in graphical region  1704  by way of example, the control device may alternatively show a video or other indication that illustrates how to move the control device within the environment during calibration. Control interface  1700  also includes selectable controls  1706  and  1708 , which respectively advance and step backward in the calibration sequence. 
     Some recording devices, such as smartphones, have microphones that are mounted towards the bottom of the device, which may position the microphone nearer to the user’s mouth during a phone call. However, when the recording device is held in a hand during the calibration procedure, such a mounting position might be less than ideal for detecting the calibration sounds. For instance, in such a position, the hand might fully or partially obstruct the microphone, which may affect the microphone measuring calibration sounds emitted by the playback device. In some cases, rotating the recording device such that its microphone is oriented upwards may improve the microphone’s ability to measure the calibration sounds. To offset the rotation, the recording device may display a control interface that is rotated 180 degrees, as shown in  FIG.  17   . Such a control interface may offset the rotation of the device so as to orient the control interface in an appropriate orientation to view and interact with the control interface. 
     As described above, during an example calibration procedure, a recording device may measure one or more first samples while moving through the environment and one or more second samples while stationary at one or more particular locations (e.g., one or more preferred listening locations). To suggest such a pattern of movement, the prompts to move the recording device may include displaying a prompt to move the control device continuously through the given environment for one or more first portions of the calibration sequence and also to remain stationary with the control device at the one or more particular locations within the given environment for one or more second portions of the calibration sequence. Such prompts may guide a user in moving the recording device during the calibration so as to measure both stationary samples and samples at a plurality of other locations within the environment (e.g., as measured while moving along a path). 
     The one or more prompts may suggest different patterns of movement to obtain such samples. In some examples, a recording device may prompt to move to a particular location (e.g., a preferred listening location) to begin the calibration. While the recording device is at that location, the recording device may measure calibration sounds emitted by the playback devices. The recording device may then prompt to move throughout the room while the recording device measures calibration sounds emitted by the playback devices. In some examples, the recording device may pause at additional locations to obtain samples at additional preferred locations. In other examples, movement of the recording device might not begin at a preferred location. Instead, the recording device may display a prompt to move throughout the room and pause at preferred listening locations. Other patterns are possible as well. 
     To illustrate such prompts, in  FIG.  18   , smartphone  500  is displaying control interface  1800  which includes graphical region  1802 . Graphical region  1802  prompts to move to a particular location (i.e., where the user will usually watch TV in the room). Such a prompt may be displayed to guide a user to begin the calibration sequence in a preferred location. Control interface  1800  also includes selectable controls  1804  and  1806 , which respectively advance and step backward in the calibration sequence. 
       FIG.  19    depicts smartphone  500  displaying control interface  1900  which includes graphical region  1902 . Graphical region  1902  prompts the user to raise the recording device to eye level. Such a prompt may be displayed to guide a user to position the phone in a position that facilitates measurement of the calibration sounds. Control interface  1800  also includes selectable controls  1904  and  1906 , which respectively advance and step backward in the calibration sequence. 
     Next,  FIG.  20    depicts smartphone  500  displaying control interface  2000  which includes graphical region  2002 . Graphical region  2002  prompts the user to “set the sweet spot.” (i.e., a preferred location within the environment). After smartphone  500  detects selection of selectable control  2004 , smartphone  500  may begin measuring the calibration sound at its current location (and perhaps also instruct one or more playback devices to output the calibration sound). As shown, control interface  2000  also includes selectable control  2006 , which advances the calibration sequence (e.g., by causing smartphone to begin measuring the calibration sound at its current location, as with selectable control  2004 ). 
     In  FIG.  21   , smartphone  500  is displaying control interface  2100  which includes graphical region  2102 . Graphical region  2102  indicates that smartphone  500  is measuring the calibration sounds. Control interface  2100  also includes selectable control  2004 , which step backwards in the calibration sequence. 
       FIG.  22    depicts smartphone  500  displaying control interface  2200  which includes graphical region  2202 . Graphical region  2202  indicates that smartphone  500  has measured the calibration sounds and that the rest of the room will be tuned using a wave and walk technique (i.e., movement through the environment). Smartphone  500  may subsequently prompt for movement through the environment, perhaps by displaying a control interface such as control interface  1700 . As shown, control interface  2200  also includes selectable control  2204 , which steps backward in the calibration sequence. 
     As indicated above, example interfaces are described in U.S. Pat. Application No. 14/696,014 filed Apr. 24, 2015, entitled “Speaker Calibration,” and U.S. Pat. Application No. 14/826,873 filed Aug. 14, 2015, entitled “Speaker Calibration User Interface,” which are incorporated herein in their entirety. 
     B. Detect Calibration Sound(s) 
     Referring again to  FIG.  16   , at block  1604 , implementation  1600  involves detecting one or more calibration sounds. For instance, the recording device may detect calibration sounds emitted by the one or more playback device during the calibration sequence. Example techniques to detect calibration sounds are described above in connection with block  1302  of implementation  1300 . 
     C. Determine Calibration 
     In  FIG.  16   , at block  1606 , implementation  1600  involves determining a calibration. For example, a processing device (e.g., the recording device) may determine two or more calibrations for the one or more playback devices (e.g., a first and a second calibration). Examples techniques to determine calibrations are described with respect to block  1304  of implementation  1300 . 
     D. Send Calibrations 
     At block  1608 , implementation  1600  involves sending one or more calibrations. For instance, the processing device may send two or more calibrations to the one or more playback devices via a network interface. The one or more playback devices may store the calibrations and apply a given one of the calibrations to playback. In embodiments in which the playback devices are configured as one or more zones, the processing device may send the calibration(s) to the zone, perhaps to be maintained by a given playback device of the zone or a device that the zone is communicatively coupled to. In some cases, the processing device may maintain the calibrations and send one or more of the calibrations to the one or more playback devices, perhaps upon request (e.g., when the playback device is applying a particular calibration). Other examples are possible as well. 
     VI. Conclusion 
     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 way(s) to implement such systems, methods, apparatus, and/or articles of manufacture. 
     (Feature 1) A method comprising: detecting, via one or more microphones during a calibration sequence: first samples including at least a portion of one or more calibration sounds as emitted by one or more playback devices of a zone while the one or more microphones are in motion in a given environment; and second samples of the one or more calibrations sounds while the one or more microphones are stationary at one or more particular locations within the given environment; determining first and second calibrations for the one or more playback devices based on at least the first and second samples, respectively; and causing at least one of the first and second calibrations to be applied to playback by the one or more playback devices. 
     (Feature 2) The method of feature 1, wherein, when applied to playback by the one or more playback devices: the first calibration is configured to offset acoustic characteristics of the given environment, and the second calibration is configured to offset acoustic characteristics of the given environment and to calibrate the one or more playback devices to the one or more particular locations. 
     (Feature 3) The method of feature 1 or 2, wherein the second calibration is determined based on a combination of the first and second samples. 
     (Feature 4) The method of feature 2 or 3, wherein calibrating the one or more playback devices to the one or more particular locations comprises one or more of: offsetting propagation delay from the one or more playback devices to the one or more particular locations, and adjusting respective gains of the one or more playback devices based on respective distances from the one or more playback devices to the one or more particular locations. 
     (Feature 5) The method of feature 4, wherein: the one or more playback devices comprise a stereo pair, and adjusting respective gains comprises balancing gain of the stereo pair to the one or more particular locations. 
     (Feature 6) The method of any preceding feature, wherein applying at least one of the first and second calibrations comprises determining one of the first and second calibrations to apply to playback based on at least one of: a determination that media content being played back consists of audio; a determination that media content being played back comprises audio and video; a determination that media content being played back is received via a physical input of a given playback device, a determination that media content being played back is from a network source; a determination that one or more listeners are located in the one or more particular locations; and a determination that a plurality of listeners are located in the given environment; and a determination that the zone is joined into a zone group with a second zone of the media playback system comprising one or more additional playback devices. 
     (Feature 7) A control device comprising: a graphical interface; one or more microphones; and a processor configured for: causing the graphical interface to display one or more prompts to instruct a user to move the control device within a given environment during a calibration sequence of a given zone that comprises one or more playback devices; performing the method of one of features 1 to 6, wherein causing at least one of the first and second calibrations to be applied comprises sending at least one of the first and second calibrations to the zone. 
     (Feature 8) The control device of feature 7, wherein recording the first samples comprises: detecting, via one or more sensors, that the control device is in motion; and recording, as respective first samples, one or more first frames corresponding to respective periods of a periodic calibration tone of the emitted calibration sounds. 
     (Feature 9) The control device of feature 7 or 8, wherein: the control device comprises one or more sensors; and recording the second samples comprises: detecting, via the one or more sensors, that control device is stationary for a threshold period of time at a given location of the one or more particular locations; and while the control device is stationary, recording, as respective second samples, one or more second frames corresponding to respective periods of a periodic calibration tone of the emitted calibration sounds. 
     (Feature 10) The control device of one of features 7 to 9, wherein the displayed one or more prompts comprise: a prompt to move the control device continuously through the given environment for one or more first portions of the calibration sequence; and a prompt to remain stationary with the control device at the one or more particular locations within the given environment for one or more second portions of the calibration sequence. 
     (Feature 11) A processor configured for use with the control device of one of features 7 to 10. 
     (Feature 12) A system comprising: a control device according to one of features 7 to 10 and at least one playback device comprising one or more processors configured for: receiving first and second calibrations; and applying the one of the first and second calibrations to playback by the playback device based on a detected given playback state of the playback device. 
     (Feature 13) The system of feature 12, wherein the at least one playback device is configured to detect a playback state that is at least one of: media content being played back consists of audio; media content being played back comprises audio and video; media content being played back is received via physical input of a given playback device, media content being played back is from a network source; one or more listeners are located in the one or more particular locations; and a plurality of listeners are located in the given environment; and a zone comprising the playback device is joined into a zone group with a second zone one or more additional playback devices. 
     (Feature 14) A playback device for use with the system of feature 12 or 13. 
     As noted above, example techniques may involve determining two or more calibrations and/or applying a given calibration to playback by one or more playback devices. A first implementation may include detecting, via one or more microphones, at least a portion of one or more calibration sounds as emitted by one or more playback devices of a zone during a calibration sequence. Such detecting may include recording first samples of the one or more calibrations sounds while the one or more microphones are in motion through a given environment and recording second samples of the one or more calibrations sounds while the one or more microphones are stationary at one or more particular locations within the given environment. The implementation may also include determining a first calibration for the one or more playback devices based on at least the first samples of the one or more calibrations sounds and determining a second calibration for the one or more playback devices based on at least the second samples of the one or more calibrations sounds. The implementation may further include applying at least one of (a) the first calibration or (b) the second calibration to playback by the one or more playback devices. 
     A second implementation may include displaying, via a graphical interface one or more prompts to move the control device within a given environment during a calibration sequence of a given zone that comprises one or more playback devices and detecting, via one or more microphones, at least a portion of one or more calibration sounds as emitted by the one or more playback devices during the calibration sequence. Such detecting may include recording first samples of the one or more calibrations sounds while the one or more microphones are in motion through the given environment and recording second samples of the one or more calibrations sounds while the one or more microphones are stationary at one or more particular locations within the given environment. The implementation may also include determining a first calibration for the one or more playback devices based on at least the first samples of the one or more calibrations sounds and determining a second calibration for the one or more playback devices based on at least the second samples of the one or more calibrations sounds. The implementation may further include sending at least one of the first calibration and the second calibration to the zone. 
     A third implementation includes a playback device receiving (i) a first calibration and (ii) a second calibration, detecting that the playback device is playing back media content in a given playback state, and applying the one of (a) the first calibration or (b) the second calibration to playback by the playback device based on the detected given playback state. 
     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 forgoing 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.