Patent Publication Number: US-11641559-B2

Title: Audio playback settings for voice interaction

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. patent application Ser. No. 15/946,585, filed on Apr. 5, 2018, entitled “Audio Playback Settings for Voice Interaction,” the contents of which are incorporated by reference herein in their entirety. 
     This application claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. patent application Ser. No. 15/277,810, filed on Sep. 27, 2016, entitled “Audio Playback Settings for Voice Interaction,” and issued as U.S. Pat. No. 9,942,678 on Apr. 20, 2018, the contents of which are incorporated by reference herein in their 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 plurality of network devices; 
         FIG.  6    shows a functional block diagram of an example network microphone device; 
         FIG.  7    shows a technique to duck audio, according to example implementations; 
         FIG.  8    shows a chart illustrating ducking of audio content; 
         FIG.  9    shows a technique to compress audio, according to example implementations; 
         FIG.  10    is a diagram illustrating ducking and compression of audio content; and 
         FIG.  11    shows a technique to equalize audio, according to example implementations. 
     
    
    
     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 
     Ambient noise may interfere with conversation between people. For instance, two people engaged in conversation in a crowded room may have difficulty understanding one another over ambient noise from other people in the room as well as other sources of sound (e.g., music or other audio content from an audio playback system). When spoken words are clearly audible over ambient noise, those spoken words can be considered to have a “good” signal-to-noise ratio (i.e., “good” enough for comprehension during a conversation). 
     Some voice services (e.g., Amazon® ALEXA®, Microsoft® CORTANA®, and Apple® SIRI®, among others now commercially available or that become available in the future) may use spoken words as input for voice control, search, and other operations. A networked microphone device (e.g., a wireless speaker, a smartphone, tablet, laptop computer, or other device) may include a microphone for detecting voice inputs and a network interface for querying a voice service with the voice input. The voice response may respond to the query with a response, which might be a spoken response played aloud by the networked microphone device via one or more speakers. As with conversations between two people, a relatively high signal-to-noise ratio may facilitate a voice service comprehending a voice input (i.e., being able to effectively parse the spoken words of the voice input into a command) and also a user comprehending a spoken response from a voice service over noise. 
     As noted above, various sources of sound may be considered noise relative to the voice input. For instance, when music is being played in a given environment while a voice input is spoken in that same environment, the music can be considered “noise” with respect to the voice input. Other sources of sound may generate ambient (e.g., background) noise while the voice input is spoken. Improving the signal-to-noise ratio of the voice input relative to these different sources of noise may improve comprehension of the voice input. 
     Improving the voice input-to-noise ratio may involve increasing the volume of the voice input or decreasing the volume of the noise, such that the volume of the voice input relative to the noise is increased. The human voice typically covers a broad frequency spectrum. However, only relatively narrow frequency bands are necessary to understand speech. The relatively narrow frequency bands include the fundamental frequencies (approximately 100 Hz for males and 180 Hz for females) and the frequencies just above. Therefore, a “good” voice input-to-noise ratio within those relatively narrow frequency bands is often sufficient for comprehension. This ratio does not necessarily need to be “good” across a broad frequency spectrum for the voice input to be comprehendible. These relatively narrow frequency bands can be referred to a speech bands. 
     Like the human voice, music typically covers a broad frequency spectrum. However, the relatively narrow frequency bands that drive speech comprehension are not as important to music consumption. Rhythm, timbre, and other compositional factors of music can be preserved when frequencies within the music that correspond to the speech bands are cut. As such, when music is being played while a voice input is spoken or a spoken response is played back, frequencies of the music corresponding to the speech bands can be ducked (i.e., temporality reduced in volume) to improve the relative volume of the voice input or spoken response within the speech bands to the music. This ducking may improve the signal-to-noise ratio without significantly compromising the music playback (the “noise”). 
     One possible drawback to lowering the volume of the music within certain frequency ranges is that the perceived loudness of the music as a whole is reduced. However, an audio playback system may offset this reduction in perceived loudness by increasing the volume in other frequency bands (e.g., in all other frequencies outside the speech bands) while the volume of the music in the speech bands is being cut. 
     Another possible drawback to lowering the volume of the music within certain frequency ranges is that some of the lower-amplitude (relatively quiet) detail in the music may drop below the noise floor (e.g., the ambient noise). Similar to how speech can be difficult to understand over music and ambient noise, portions of the music might be difficult to understand over the noise floor (e.g., conversations between people, appliances, HVAC, outdoor noise such as traffic, among other possible sources). Losing low-amplitude fine detail in the music below the noise floor may impact enjoyment of the music. 
     In some implementations, the audio playback system may compress the music to bring the low-amplitude fine detail above the noise floor. The audio playback system may measure the ambient noise level, which relative to the music might include human speech. Then, the music may be compressed to increase the level of the low-amplitude fine detail above the noise floor. While compression might not preserve all detail, compressing the music may preserve some low-amplitude fine detail that would have been otherwise inaudible over the noise floor. 
     As noted above, speech may be difficult to comprehend in the presence of noise (e.g., music playback or other ambient noise). As such, some example techniques noted above may involve an audio playback system ducking music or other audio content to improve the signal-to-noise ratio of speech (e.g., voice inputs and spoken responses) relative to this noise, which may render the speech more comprehendible. More generally, music playback within an environment may make speech by two or more people attempting a conversation difficult to understand. In an attempt to alleviate this issue, an audio playback system may apply an equalization that improves the signal-to-noise (i.e., speech-to-music) ratio. This equalization may cut frequencies of music within the speech bands (i.e., the fundamental frequencies and those slightly above). The equalization may also boost frequencies outside the speech bands in an attempt to maintain the perceived loudness of the music when portions of the music within the speech bands are cut. 
     Since such an equalization changes the characteristics of the music being played back, some users may prefer that this equalization is not always applied. Rather, such users might prefer that the equalization is applied when speech is present. Speech within a given environment might include a conversation between two people in the environment, a telephone conversation between one person in the environment and other person somewhere else, speech from a voice-capable artificial intelligence (e.g. a spoken response from a voice service), among other examples. In some implementation, an audio playback system may include one or more microphones to detect speech. Alternatively, the audio playback system may use sensors to detect the number of people within the environment, which may indirectly indicate the presence of speech (i.e., the system may assume that the volume of speech within an environment increases with the number of possible speakers within that environment). When speech is detected, the audio playback system may apply the equalization to improve the signal-to-noise ratio of the speech to noise. 
     Example techniques may involve improving signal-to-noise ratio of speech to noise, such as music. A first implementation may include a playback device playing back first audio in a given environment at a given loudness, and while playing back the first audio: (a) detecting that an event is anticipated in the given environment, the event involving playback of second audio and (b) determining a loudness of background noise in the given environment, wherein the background noise comprises ambient noise in the given environment. The first implementation may further include ducking the first audio in proportion to a difference between the given loudness of the first audio and the determined loudness of the background noise. The first implementation may also include playing back the ducked first audio concurrently with the second audio. 
     A second implementation may include a playback device determining a loudness of first audio being played back by the playback device and a loudness of background noise in a given environment. The second implementation may also include determining whether a difference between a loudness of the first audio and a given dynamic range is (a) less than a determined loudness of the background noise or (b) greater than the determined loudness of the background noise. When the determined difference between the loudness of the ducked first audio and the given dynamic range is less than the determined loudness of the background noise, the second implementation may further include compressing the first audio to a dynamic range that is louder than the determined loudness of the background noise and playing back the compressed first audio. When the determined difference between the loudness of the first audio and the given dynamic range is greater than the determined loudness of the background noise, the second implementation may include playing back the first audio without compression. 
     A third implementation may involve a playback device playing audio content. While playing audio, the playback device may detect that a signal-to-noise ratio in the given environment is below a speech threshold. While the signal-to-noise ratio in the given environment is below a speech threshold, the playback device may apply an equalization to the audio content. The equalization may cut certain frequency bands corresponding to human speech. The equalization may also boost other frequency bands not corresponding to human speech. 
     Each of the these example implementations may be embodied as a method, a device configured to carry out the implementation, a system of devices 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. Further, any example operation described as being performed by a given device to illustrate a technique may be performed by any suitable devices, including the devices described herein. Yet further, any device may cause another device to perform any of the operations 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 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118 ,  120 ,  122 ,  124 , control devices  126  and  128 , a wired or wireless network router  130 , and a networked microphone device  132 . 
     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, 802.11g, 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 802.11a, 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. 
     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 Plurality of Networked Devices 
       FIG.  5    shows an example plurality of devices  500  that may be configured to provide an audio playback experience based on voice control. One having ordinary skill in the art will appreciate that the devices shown in  FIG.  5    are for illustrative purposes only, and variations including different and/or additional devices may be possible. As shown, the plurality of devices  500  includes computing devices  504 ,  506 , and  508 ; network microphone devices (NMDs)  512 ,  514 , and  516 ; playback devices (PBDs)  532 ,  534 ,  536 , and  538 ; and a controller device (CR)  522 . 
     Each of the plurality of devices  500  may be network-capable devices that can establish communication with one or more other devices in the plurality of devices according to one or more network protocols, such as NFC, Bluetooth, Ethernet, and IEEE 802.11, among other examples, over one or more types of networks, such as wide area networks (WAN), local area networks (LAN), and personal area networks (PAN), among other possibilities. 
     As shown, the computing devices  504 ,  506 , and  508  may be part of a cloud network  502 . The cloud network  502  may include additional computing devices. In one example, the computing devices  504 ,  506 , and  508  may be different servers. In another example, two or more of the computing devices  504 ,  506 , and  508  may be modules of a single server. Analogously, each of the computing device  504 ,  506 , and  508  may include one or more modules or servers. For ease of illustration purposes herein, each of the computing devices  504 ,  506 , and  508  may be configured to perform particular functions within the cloud network  502 . For instance, computing device  508  may be a source of audio content for a streaming music service. 
     As shown, the computing device  504  may be configured to interface with NMDs  512 ,  514 , and  516  via communication path  542 . NMDs  512 ,  514 , and  516  may be components of one or more “Smart Home” systems. In one case, NMDs  512 ,  514 , and  516  may be physically distributed throughout a household, similar to the distribution of devices shown in  FIG.  1   . In another case, two or more of the NMDs  512 ,  514 , and  516  may be physically positioned within relative close proximity of one another. Communication path  542  may comprise one or more types of networks, such as a WAN including the Internet, LAN, and/or PAN, among other possibilities. 
     In one example, one or more of the NMDs  512 ,  514 , and  516  may be devices configured primarily for audio detection. In another example, one or more of the NMDs  512 ,  514 , and  516  may be components of devices having various primary utilities. For instance, as discussed above in connection to  FIGS.  2  and  3   , one or more of NMDs  512 ,  514 , and  516  may be the microphone(s)  220  of playback device  200  or the microphone(s)  310  of network device  300 . Further, in some cases, one or more of NMDs  512 ,  514 , and  516  may be the playback device  200  or network device  300 . In an example, one or more of NMDs  512 ,  514 , and/or  516  may include multiple microphones arranged in a microphone array. 
     As shown, the computing device  506  may be configured to interface with CR  522  and PBDs  532 ,  534 ,  536 , and  538  via communication path  544 . In one example, CR  522  may be a network device such as the network device  200  of  FIG.  2   . Accordingly, CR  522  may be configured to provide the controller interface  400  of  FIG.  4   . Similarly, PBDs  532 ,  534 ,  536 , and  538  may be playback devices such as the playback device  300  of  FIG.  3   . As such, PBDs  532 ,  534 ,  536 , and  538  may be physically distributed throughout a household as shown in  FIG.  1   . For illustration purposes, PBDs  536  and  538  may be part of a bonded zone  530 , while PBDs  532  and  534  may be part of their own respective zones. As described above, the PBDs  532 ,  534 ,  536 , and  538  may be dynamically bonded, grouped, unbonded, and ungrouped. Communication path  544  may comprise one or more types of networks, such as a WAN including the Internet, LAN, and/or PAN, among other possibilities. 
     In one example, as with NMDs  512 ,  514 , and  516 , CR  522  and PBDs  532 ,  534 ,  536 , and  538  may also be components of one or more “Smart Home” systems. In one case, PBDs  532 ,  534 ,  536 , and  538  may be distributed throughout the same household as the NMDs  512 ,  514 , and  516 . Further, as suggested above, one or more of PBDs  532 ,  534 ,  536 , and  538  may be one or more of NMDs  512 ,  514 , and  516 . 
     The NMDs  512 ,  514 , and  516  may be part of a local area network, and the communication path  542  may include an access point that links the local area network of the NMDs  512 ,  514 , and  516  to the computing device  504  over a WAN (communication path not shown). Likewise, each of the NMDs  512 ,  514 , and  516  may communicate with each other via such an access point. 
     Similarly, CR  522  and PBDs  532 ,  534 ,  536 , and  538  may be part of a local area network and/or a local playback network as discussed in previous sections, and the communication path  544  may include an access point that links the local area network and/or local playback network of CR  522  and PBDs  532 ,  534 ,  536 , and  538  to the computing device  506  over a WAN. As such, each of the CR  522  and PBDs  532 ,  534 ,  536 , and  538  may also communicate with each over such an access point. 
     In one example, a single access point may include communication paths  542  and  544 . In an example, each of the NMDs  512 ,  514 , and  516 , CR  522 , and PBDs  532 ,  534 ,  536 , and  538  may access the cloud network  502  via the same access point for a household. 
     As shown in  FIG.  5   , each of the NMDs  512 ,  514 , and  516 , CR  522 , and PBDs  532 ,  534 ,  536 , and  538  may also directly communicate with one or more of the other devices via communication means  546 . Communication means  546  as described herein may involve one or more forms of communication between the devices, according to one or more network protocols, over one or more types of networks, and/or may involve communication via one or more other network devices. For instance, communication means  546  may include one or more of for example, Bluetooth™ (IEEE 802.15), NFC, Wireless direct, and/or Proprietary wireless, among other possibilities. 
     In one example, CR  522  may communicate with NMD  512  over Bluetooth™, and communicate with PBD  534  over another local area network. In another example, NMD  514  may communicate with CR  522  over another local area network, and communicate with PBD  536  over Bluetooth. In a further example, each of the PBDs  532 ,  534 ,  536 , and  538  may communicate with each other according to a spanning tree protocol over a local playback network, while each communicating with CR  522  over a local area network, different from the local playback network. Other examples are also possible. 
     In some cases, communication means between the NMDs  512 ,  514 , and  516 , CR  522 , and PBDs  532 ,  534 ,  536 , and  538  may change depending on types of communication between the devices, network conditions, and/or latency demands. For instance, communication means  546  may be used when NMD  516  is first introduced to the household with the PBDs  532 ,  534 ,  536 , and  538 . In one case, the NMD  516  may transmit identification information corresponding to the NMD  516  to PBD  538  via NFC, and PBD  538  may in response, transmit local area network information to NMD  516  via NFC (or some other form of communication). However, once NMD  516  has been configured within the household, communication means between NMD  516  and PBD  538  may change. For instance, NMD  516  may subsequently communicate with PBD  538  via communication path  542 , the cloud network  502 , and communication path  544 . In another example, the NMDs and PBDs may never communicate via local communications means  546 . In a further example, the NMDs and PBDs may communicate primarily via local communications means  546 . Other examples are also possible. 
     In an illustrative example, NMDs  512 ,  514 , and  516  may be configured to receive voice inputs to control PBDs  532 ,  534 ,  536 , and  538 . The available control commands may include any media playback system controls previously discussed, such as playback volume control, playback transport controls, music source selection, and grouping, among other possibilities. In one instance, NMD  512  may receive a voice input to control one or more of the PBDs  532 ,  534 ,  536 , and  538 . In response to receiving the voice input, NMD  512  may transmit via communication path  542 , the voice input to computing device  504  for processing. In one example, the computing device  504  may convert the voice input to an equivalent text command, and parse the text command to identify a command. Computing device  504  may then subsequently transmit the text command to the computing device  506 . In another example, the computing device  504  may convert the voice input to an equivalent text command, and then subsequently transmit the text command to the computing device  506 . The computing device  506  may then parse the text command to identify one or more playback commands. 
     For instance, if the text command is “Play ‘Track 1’ by ‘Artist 1’ from ‘Streaming Service 1’ in ‘Zone 1’,” The computing device  506  may identify (i) a URL for “Track 1” by “Artist 1” available from “Streaming Service 1,” and (ii) at least one playback device in “Zone 1.” In this example, the URL for “Track 1” by “Artist 1” from “Streaming Service 1” may be a URL pointing to computing device  508 , and “Zone 1” may be the bonded zone  530 . As such, upon identifying the URL and one or both of PBDs  536  and  538 , the computing device  506  may transmit via communication path  544  to one or both of PBDs  536  and  538 , the identified URL for playback. One or both of PBDs  536  and  538  may responsively retrieve audio content from the computing device  508  according to the received URL, and begin playing “Track 1” by “Artist 1” from “Streaming Service 1.” 
     One having ordinary skill in the art will appreciate that the above is just one illustrative example, and that other implementations are also possible. In one case, operations performed by one or more of the plurality of devices  500 , as described above, may be performed by one or more other devices in the plurality of device  500 . For instance, the conversion from voice input to the text command may be alternatively, partially, or wholly performed by another device or devices, such as NMD  512 , computing device  506 , PBD  536 , and/or PBD  538 . Analogously, the identification of the URL may be alternatively, partially, or wholly performed by another device or devices, such as NMD  512 , computing device  504 , PBD  536 , and/or PBD  538 . 
     f. Example Network Microphone Device 
       FIG.  6    shows a functional block diagram of an example network microphone device  600  that may be configured to be one or more of NMDs  512 ,  514 , and  516  of  FIG.  5   . As shown, the network microphone device  600  includes a processor  602 , memory  604 , a microphone array  606 , a network interface  608 , a user interface  610 , software components  612 , and speaker(s)  614 . One having ordinary skill in the art will appreciate that other network microphone device configurations and arrangements are also possible. For instance, network microphone devices may alternatively exclude the speaker(s)  614  or have a single microphone instead of microphone array  606 . 
     The processor  602  may include one or more processors and/or controllers, which may take the form of a general or special-purpose processor or controller. For instance, the processing unit  602  may include microprocessors, microcontrollers, application-specific integrated circuits, digital signal processors, and the like. The memory  604  may be data storage that can be loaded with one or more of the software components executable by the processor  602  to perform those functions. Accordingly, memory  604  may comprise one or more non-transitory computer-readable storage mediums, examples of which may include volatile storage mediums such as random access memory, registers, cache, etc. and non-volatile storage mediums such as read-only memory, a hard-disk drive, a solid-state drive, flash memory, and/or an optical-storage device, among other possibilities. 
     The microphone array  606  may be a plurality of microphones arranged to detect sound in the environment of the network microphone device  600 . Microphone array  606  may include any type of microphone now known or later developed such as a condenser microphone, electret condenser microphone, or a dynamic microphone, among other possibilities. In one example, the microphone array may be arranged to detect audio from one or more directions relative to the network microphone device. The microphone array  606  may be sensitive to a portion of a frequency range. In one example, a first subset of the microphone array  606  may be sensitive to a first frequency range, while a second subset of the microphone array may be sensitive to a second frequency range. The microphone array  606  may further be arranged to capture location information of an audio source (e.g., voice, audible sound) and/or to assist in filtering background noise. Notably, in some embodiments the microphone array may consist of only a single microphone, rather than a plurality of microphones. 
     The network interface  608  may be configured to facilitate wireless and/or wired communication between various network devices, such as, in reference to  FIG.  5   , CR  522 , PBDs  532 - 538 , computing device  504 - 508  in cloud network  502 , and other network microphone devices, among other possibilities. As such, network interface  608  may take any suitable form for carrying out these functions, examples of which may include an Ethernet interface, a serial bus interface (e.g., FireWire, USB 2.0, etc.), a chipset and antenna adapted to facilitate wireless communication, and/or any other interface that provides for wired and/or wireless communication. In one example, the network interface  608  may be based on an industry standard (e.g., infrared, radio, wired standards including IEEE 802.3, wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4G mobile communication standard, and so on). 
     The user interface  610  of the network microphone device  600  may be configured to facilitate user interactions with the network microphone device. In one example, the user interface  608  may include one or more of physical buttons, graphical interfaces provided on touch sensitive screen(s) and/or surface(s), among other possibilities, for a user to directly provide input to the network microphone device  600 . The user interface  610  may further include one or more of lights and the speaker(s)  614  to provide visual and/or audio feedback to a user. In one example, the network microphone device  600  may further be configured to playback audio content via the speaker(s)  614 . 
     Moving now to several example implementations, implementations  700 ,  900  and  1100  shown in  FIGS.  7 ,  9 , and  11   , 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  700 ,  900 , and  1100  may include one or more operations, functions, or actions as illustrated by one or more of blocks shown in  FIGS.  7 ,  9 , and  11   . 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 Duck Audio 
     As discussed above, embodiments described herein may facilitate speech comprehension in the presence of noise, such as music playback.  FIG.  7    illustrates an example implementation  700  by which a playback device ducks audio being played back. Such ducking may improve speech comprehension in the presence of the played back audio. 
     a. Detect that an Event is Anticipated in a Given Environment 
     At block  702 , implementation  700  involves detecting that an event is anticipated in a given environment. For instance, a playback device, such as playback device  114  of media playback system  100 , may detect that an event is anticipated in a given environment (e.g., within the example home environment or a subset of its rooms and spaces, such as in the Kitchen). Such an anticipated event may be an event that is expected or predicted to occur but has not yet taken place (or perhaps has not fully taken place). During the event (or a portion thereof), audio that is being played by one or more playback devices of a media playback system (e.g., any of playback devices  102 - 124  of media playback system  100 ) may be ducked. Ducking is an audio effect by which the level of one audio signal is reduced during the presence of another audio signal. 
     As noted above, audio that is being played back may be ducked. Implementation  700  may involve detecting that an event is anticipated while playing back first audio in the given environment. The first audio might be music, talk radio or other programming, television or home theater content, audio from an analog or digital line-in to the playback device, as well as other types of audio or a combination of multiple types of audio. Ultimately, the playback device may duck the first audio during the event (or during a portion of the event). 
     Some example events may involve playback of second audio. Detecting that such an event is anticipated may involve detecting that playback of the second audio is anticipated. A playback device may anticipate playback of second audio when the playback device receives an instruction to playback the second audio via a network interface (and/or receives the second audio itself for playback, perhaps as an audio stream). Alternatively, a first playback device (e.g., playback device  112 ) may detect that playback of the second audio by one or more second playback devices is anticipated, perhaps by receiving a transmission indicating that the one or more second playback devices (e.g., one or more of the playback devices of media playback system  100 ) are expected to play back second audio. 
     In some cases, the second audio may be related to a voice service. Some voice services include artificial intelligence to process voice inputs and generate responses to those voice inputs. For instance, the second audio may include a spoken voice input to a voice service (e.g., “Hey Kitchen, what is the weather today?”). The second audio may additionally or alternatively include a spoken response to a voice input (e.g., “The weather is clear and sunny with a high of 75 degrees and a low of 68 degrees”). The playback device may receive such a response via a network interface from a voice service or from an NMD, among other sources. 
     Detecting that an event is anticipated in a given environment may involve receiving an indication that a voice command with the given environment is anticipated. For instance, an NMD (e.g., NMD  132  of  FIG.  1   ) may detect a voice input and transmit an indication to playback device  114  that second audio is anticipated. Detecting that an event is anticipated in the given environment may involve receiving that indication. 
     In some cases, a voice input may include a wake word and a voice command. Detection of a spoken wake-word (e.g., “Hey Siri,” “Ok, Google,” “Sonos,” or “Hey, Alexa,” among others) may cause a NMD to start listening for a voice command. As such, detection of a wake word may indicate that a voice command is expected in the given environment. A playback device may detect that an event (e.g., a voice command and/or an audio response to the voice command) is anticipated by receiving an indication from an NMD that a wake word was detected. Alternatively, an NMD may be integrated with a playback device. In such implementations, the playback device may detect that an event is anticipated by detecting a voice input via one or more microphones (e.g., a far-field microphone array). The voice input or a portion thereof (e.g., a wake-word) may cause the playback device to anticipate the event (e.g., second audio include a voice command and/or an audio response to the voice command). 
     The second audio might include other audio streams as well. Example streams include any stream from a cloud services (e.g., a stream from a home cloud service indicating that a “smart” device (e.g., an appliance or other smart home device with an processor and network interface) is experiencing a condition. For instance, “smart” thermostat may cause a various audio streams indicating respective conditions to be played back (e.g., “HVAC system cooling” or “HVAC system fault”). 
     Other example streams may be sent from other network-connected devices within the environment. For instance, a “smart” doorbell may instruct the playback device to output a doorbell track (e.g., a chime) perhaps by streaming the doorbell track to the playback device. As another example, a “smart” refrigerator may stream a spoken message (e.g., a message indicating that certain food is past its expiration date). Detecting that an event is anticipated may involve receiving an instruction to play back such a stream, receiving the stream itself, or receiving an indication that another playback device is instructed to play back the stream, among other examples. 
     In some examples, detecting that an event is anticipated may involve detecting input data from one or more control interfaces (e.g., controller interface  400  displayed on a control device or a physical button on a playback device, among other options). The input data may indicate an instruction that causes the playback device to play back second audio. As noted above, the second audio may include a spoken response from a voice service, an audio stream from a “smart” device, or an audio stream from a cloud service, among other examples. For instance, a remote control may include a microphone button that causes the remote control to start listening for a voice input via one or more microphones. Detecting a press of such a button may cause the playback device to anticipate an event that involves second audio within the environment (e.g., a voice input and/or an audio response to that voice input). 
     As noted above, a playback device may detect that the event is anticipated while playing back first audio in the given environment. For instance, playback device  114  of media playback system  100  in  FIG.  1    may stream first audio and play the streamed audio in the Kitchen. In some cases, the playback device may be part of a grouping of playback devices, such as a bonded zone or zone group. In such cases, playing back first audio in the given environment may involve playing audio in synchrony with other playback devices in the grouping. For instance, playback devices  104 ,  106 ,  108 , and  110  may play back respective channels of first audio that includes surround sound (e.g., home theater) audio. As another example, playback devices  104 ,  106 ,  108 ,  110 ,  112  and  114  may be joined into a zone group to play music in synchrony. Many examples are possible. 
     b. Determine Loudness of Background Noise in Given Environment 
     Referring back to  FIG.  7   , at block  704 , implementation  700  involves determining a loudness of background noise in the given environment. For instance, the playback device may measure background noise in the given environment using one or more microphones. Alternatively, the playback device may transmit a request that causes one or more NMDs to measure background noise in the given environment. The background noise may include ambient noise within the given environment (e.g., conversations between people, appliances, HVAC, outdoor noise such as traffic, among other possible sources). The playback device may determine loudness while playing back the first audio in the given environment. 
     In some cases, multiple NMDs may perform the measurement of background noise. For instance, the playback device may transmit to multiple NMDs respective requests to measure background noise. Alternatively, one or more first NMDs may receive an instruction to measure background noise and cause one or more second NMDs to measure background noise. The NMDs may measure the background noise using one or more microphones (e.g., using a far-field microphone array). For instance, NMD  132  and control devices  126  shown in Figure (which may have an integrated NMD) may each perform a measurement of background noise within the Living Room/Dining Room/Kitchen environment. 
     A suitable processing device, such as the playback device or an NMD, may combine multiple measurements of background noise to yield a representation of loudness of background noise in the given environment. In some cases, the processing device may average multiple measurements of background noise to determine the loudness. In some cases, measurements from respective NMDs may be weighted (e.g., prioritized) differently, perhaps based on the quality of measurement. Quality of measurement may vary based on an NMD&#39;s position within the given environment (which may influence how well the NMD is able to measure background noise), the quality of microphone(s) used to measure background noise, or other factors that might influence measurement quality. 
     In some implementations, the processing device may offset the first audio that the playback device is playing back within the measurement of background noise in the given environment. By offsetting the first audio from the measurement, the measurement may more accurately represent the ambient noise other than the first audio that is present within the environment. 
     Various techniques may be used to offset the first audio from the measurement. For instance, the measurement may use acoustic echo cancellation or beam-forming to offset the first audio from the measurement, among other suitable recording techniques. Alternatively, the acoustic response of the playback device and the first audio may each be known, such that the response produced by the playback device in playing back the first audio is known (to at least some approximate degree). With this response known, the processing device can offset the first audio from a measurement of background noise by subtraction. Other techniques are possible as well. 
     In some cases, the measurement device(s) and/or the processing device(s) may transmit measurement(s) of background noise to the playback device. This measurement may be represented as a decibel value of a known scale or an identifier of a range (e.g., a loudness-window) in which the loudness measurement falls, among any suitable indication of the measured loudness. In some cases, the transmission may represent an error state indicating that a loudness measurement could not be obtained. 
     As indicated above, in some cases, the playback device might not be able to obtain a loudness measurement. For instance, there might not be any suitable NMDs within the given environment to perform the measurement. Or, as another example, there may be a connection issue between NMDs within the given environment and the playback device. Other issues are possible as well. 
     When the playback device is unable to obtain a measurement of the background noise, the playback device may estimate the background noise. For instance, the playback device may estimate the background noise as some default background noise level. Alternatively, the playback device may estimate the background noise as the last known background noise level within the environment. 
     As yet another example, the playback device may estimate the background noise based on a measurement of background noise in another room. For example, playback device  114  may estimate background noise in the Living Room/Dining Room/Kitchen environment using a measurement of background noise in the Bedroom environment from control device  128 . The estimate of background noise in the Living Room/Dining Room/Kitchen environment based the measurement of background noise in the Bedroom environment may be adjusted based on the relative locations of two environments and any obstructions between the two environments, which may be known. Emitting sound in one environment and recording that sound in another may facilitate mapping transforms between environments (e.g., between rooms or spaces). 
     c. Duck the First Audio 
     In  FIG.  7   , at block  706 , implementation  700  involves ducking the first audio. For instance, the playback device may duck the first audio that is being played back by the playback device. As noted above, ducking is an audio effect by which the level of one audio signal is reduced during the presence of another audio signal. As used herein, ducking may refer to volume reduction of the first audio that the playback device is playing back during the anticipated event. For example, the playback device may reduce the volume of the first audio while the second audio is present (e.g., playing back or being spoken). 
     As noted above, in some instances, the anticipated event may involve second audio. The second audio may include a voice input and/or a spoken response from a voice service to a voice input. In some examples, the playback device ducks the first audio (e.g., one or more audio tracks, such as music) during the voice input and/or during the spoken response from the voice service. Such ducking may assist an NMD in comprehending the voice input and/or a user in comprehending a spoken response. 
     The amount of ducking (i.e., the amount of volume reduction of the first audio) may vary based on desired outcomes of the ducking. For instance, the loudness of the first audio may be reduced to the volume level of the second audio such that the first audio and the second audio are output at approximately equal loudness levels. Other examples are possible. 
     In some examples, the first audio may be ducked by a specific amount based on the difference between loudness of the first audio and the background noise. For instance, where the playback device is playing back the first audio at a given loudness, the playback device may duck the first audio in proportion to the difference between the given loudness and the determined loudness of the background noise. Ducking the first audio by such an amount may assist in keeping the ducked first audio above the noise floor. 
     To illustrate, in one example a party might be held in the Living Room/Dining Room/Kitchen area shown in  FIG.  1   . During the party, playback devices  104 ,  106 ,  108 ,  110 ,  112 , and/or  114  may play back first audio (e.g., music) at a given volume level. Music played at that volume level may generate a dynamic range centered around a given loudness. The dynamic range of the first audio is the difference between the quiet and loudest parts of the first audio. Talking, dancing, and/or other actions by guests at the party may generate a relatively high level of background noise. Given this relatively loud background noise, if the first audio is set at a relatively low volume, some part of the first audio (i.e., the quiet parts of music at the low end of the dynamic range) may be below the noise floor. Alternatively, if the first audio is set at a relatively high volume, more (or all) of the first audio may be above the noise floor. When the first audio is ducked, the quieter parts of the first audio may go below the noise floor. Ducking the first audio in proportion to the difference between the given loudness and the determined loudness of the background noise may help to avoid portions of the first audio being lost under the noise floor. 
     As noted above, in some examples, the playback device may duck the first audio while the second audio is present.  FIG.  8    includes a chart  800 . In chart  800 , time is plotted along the x-axis and loudness is plotted along the y-axis. At time t 0 , a playback device is playing first audio  802  at loudness level l 0 . From time t 1  to time t 2 , the playback device reduces the loudness of first audio  802  from loudness level l 0  to loudness level l 1  so as to duck the first audio  802  in the presence of second audio  804 . 
     In some cases, the playback device may duck the first audio itself. For instance, the playback device may adjust an amplifier level to reduce the volume of the first audio. Alternatively, the playback device may apply a filter to reduce the volume of the first audio. As yet another example, another device may process the first audio to reduce the volume of the first audio. Other examples are possible as well. 
     d. Play Back the Ducked First Audio Concurrently with the Second Audio 
     In  FIG.  7   , at block  708 , implementation  700  involves playing back the ducked first audio concurrently with the second audio. For instance, the playback device may receive a stream of the second audio and play back that stream of second audio concurrently with the ducked first audio. As noted above, a playback device may receive a spoken response to a voice input from a voice service or intermediary device. The playback device may play back ducked music (e.g., one or more audio tracks) concurrently with the spoken response from a voice input. As another example, the playback device may play back a ducked streaming radio station concurrently with an alarm from a “smart” device such as a doorbell or refrigerator. In a further example, the second audio may be a phone call and the playback device may play back audio from the phone call concurrently with the ducked first audio. As noted above, many different types of first and second audio are contemplated. 
     As noted above, a playback device may be part of grouping of playback devices, such as a bonded zone or zone group. In such cases, the playback device may play the first audio in synchrony with other playback devices in the grouping. In some implementations, all of the playback devices in the grouping may play back the ducked first audio concurrently with the second audio. In other implementations, a subset of the playback devices in the grouping may play back the ducked first audio concurrently with the second audio, while the other playback devices continue to play back the first audio without ducking. In yet further examples, a subset of the playback devices in the grouping may play back the second audio while the other playback devices play back the first audio. Other examples are possible as well. 
     The playback device may continue to duck the first audio until the anticipated event has completed or until a future event occurs, among other examples. For instance, if the event is a voice interaction with a voice service, the playback device may duck the first audio while a user is speaking a voice input and/or while playing back a spoken response from the voice service. As another example, if the event is a phone call, the playback device may duck the first audio until the phone call ends (e.g., until the parties hang up). Generally, in examples where the second audio is an audio stream, the playback device may duck the first audio until the second audio completes play back. 
     To illustrate, referring back to  FIG.  8   , the second audio  804  is output from time t 2  to t 3 . The first audio  802  is ducked from time t 2  until t 3 . Time t 3  may correspond to the end of the anticipated event beginning at t 2  or to a future event detected by the playback device. From time t 3  to t 4 , the ducking is reversed by raising the volume level from l 1  to l 2 . 
     IV. Example Techniques to Compress Audio 
     As discussed above, embodiments described herein may facilitate compressing audio in the presence of second audio.  FIG.  9    illustrates an example implementation  900  by which a playback device compresses first audio. The playback device may compress the first audio while ducking the first audio, as described above in connection with implementation  700 . 
     a. Determine Loudness of First Audio and Background Noise 
     At block  902 , implementation  900  involves determining a loudness of first audio and background noise in a given environment. For instance, a playback device may determine the loudness of first audio played back by the playback device (and possibly one or more additional playback devices in synchrony with the playback device). The first audio may be any suitable audio, such as any of the examples of first audio discussed above in connection with implementation  700 , among other examples. The playback device may determine a loudness of background noise using any suitable technique, such as the example techniques described in connection with block  704  of implementation  700 . 
     In some instances, the first audio may be ducked first audio, such as the ducked first audio discussed above in connection with implementation  700 . Ducked first audio may refer to audio that has been temporarily reduced in volume based on the presence of second audio. 
     The playback device may determine the loudness of the first audio using any suitable technique. For instance, the playback device may have a known volume setting (perhaps reduced by a known amount through ducking). The playback device may have a known equalization. Furthermore, the playback device may have a known response in the given environment, perhaps via a calibration procedure. The first audio may have a known or assumed level (e.g., −6 dB from an average master). Given one or more of these known values, the playback device may estimate the loudness of the first audio. 
     b. Compare Determined Loudness of First Audio with Loudness of Background Noise 
     In  FIG.  9   , at block  904 , implementation  900  involves comparing the determined loudness of the first audio with the determined loudness of the background noise. For instance, a playback device may determine a difference between a loudness of first audio (possibly ducked first audio) and a given dynamic range. The playback device may further determine whether the difference between the loudness of the (ducked) first audio and the given dynamic range is less than or greater than the determined loudness of the background noise. The given dynamic range may be a desired dynamic range of the first audio (e.g., a dynamic range of music playback). 
     c. Compressing First Audio 
     In  FIG.  9   , at block  906 , implementation  900  involves compressing the first audio. The playback device may compress the first audio when the determined difference between the loudness of the (ducked) first audio and the given dynamic range is less than the determined loudness of the background noise. This determination may indicate that a portion of the dynamic range of the first audio is below the noise floor created by the background noise. By compressing the first audio in such circumstances, some or all of the dynamic range of the first audio may be raised above the noise floor. When the determined difference between the loudness of the (ducked) first audio and the given dynamic range is greater than the determined loudness of the background noise, the playback might not apply compression since such compression might be unnecessarily reduce the dynamic range of the first audio. 
     The amount of compression may be a function of the difference between the determined loudness of the background noise and the given dynamic range. For instance, when the difference is relatively large such that the low end of the dynamic range is relatively further below the noise floor created by the background noise, then the playback device may compress the first audio more to bring more (or all) of the dynamic range above the noise floor. Conversely, when the difference is relatively small such that the low end of the dynamic range is just below the noise floor, the playback device might compress the dynamic range of the first audio relatively less. 
     To illustrate,  FIG.  10    is a diagram illustrating a dynamic range  1000 A of first audio (e.g., music) and a dynamic range  1002 A of second audio (e.g., voice). As shown, dynamic range  1000 A and dynamic range  1002  overlap, which may make the first audio and/or the second audio hard to comprehend. At time t 1 , the first audio is ducked, which causes a dynamic range  1000 B of the ducked first audio to be below the dynamic range  1002  of the second audio. However, when ducked, the dynamic range of the first audio is below a noise floor  1004 . In this case, quiet details in the first audio may be indiscernible over background noise. At time t 2 , the ducked first audio is compressed, which causes a dynamic range  1000 C of the ducked and compressed audio to be above the noise floor  1004 . Although  FIG.  10    describes ducking and compression as occurring in a particular order, these operations may be performed concurrently or in a different order. 
     Although examples techniques described in connection with implementation  1000  describe compression being applied based on a comparison between the determined loudness of background noise and the first audio, compression may be applied to the first audio under other conditions as well. For instance, compression may be applied based on content type (e.g., applied to music or talk radio) or background noise level, among other options. In some cases, compression is always applied to first audio when second audio is present. 
     V. Example Techniques to Apply Equalization 
     As discussed above, embodiments described herein may improve speech-to-noise ratio within a given environment.  FIG.  11    illustrates an example implementation  1100  by which a playback device selectively applies an equalization to audio content being played back. 
     a. Play Audio Content in Given Environment 
     At block  1102 , implementation  1100  involves playing audio content in a given environment. For instance, one or more playback devices (e.g., any combination of playback devices  102 - 124  in  FIG.  1   ) may play back audio content in one or more rooms of the example home environment in  FIG.  1   . In one example, playback devices  112  and  114  may play back music in the Kitchen/Dining Room environment. The audio content may be music or any other suitable audio content. 
     b. Detect that a Signal-to-Noise Ratio in Given Environment is Below Speech Threshold 
     In  FIG.  11   , at block  1104 , implementation  1100  involves detecting that a signal-to-noise ratio in the given environment is below a speech threshold. For instance, a playback device (e.g., playback device  114  of  FIG.  1   ) may determine that a signal-to-noise ratio in a given environment (i.e., the Kitchen or the combined Dining Room/Kitchen area) is below a speech threshold. A signal-to-noise ratio that is below the speech threshold may indicate that an improvement to signal-to-noise ratio in the given environment would facilitate comprehension of speech in that environment. 
     In some implementations, detecting that the signal-to-noise ratio in the given environment is below the speech threshold may involve detecting a number of people in the given environment. The playback device may assume that the signal-to-noise ratio in the given environment is below the speech threshold when there are more than a given number of people in the room (e.g., two or more). The playback device may detect a number of people in the environment by detecting signals from their respective smartphones or other devices using a network interface (e.g., using Bluetooth® beacons or WiFi® device detection). In another case, the playback device may detect sound pressure level of background noise in the given environment, perhaps by querying one or more NMDs for a measurement. A high sound pressure level of background noise may indicate that the signal-to-noise ratio in the given environment is below the speech threshold. In further implementations, user input may indicate a number of persons in the environment. 
     In other cases, the playback device may anticipate that speech will be present in the environment. For example, the playback device may receive an indication of a wake-word in the given environment, which may cause the playback device to anticipate a voice command. In other examples, the playback device may receive an audio stream representing speech to be played back by the playback device. Alternatively, the playback device may receive an indication that another playback device in the environment is outputting speech. The speech may be audio of a telephone call or a spoken response from a voice service, among other examples of human or computer-generated speech. When speech is present in the environment, the playback device may assume that the signal-to-noise ratio in the given environment is below the speech threshold. 
     c. Apply Equalization to Audio Content 
     In  FIG.  11   , at block  1106 , implementation  1100  involves applying an equalization to the audio content. For instance, playback device  114  may filter the audio content (e.g., using one or more digital or analog filters) to a particular equalization. The equalization may cut the audio content at frequencies in the audio content corresponding to human speech (e.g., 150 Hz-3 kHz). Such filtering may include filtering at the fundamental frequencies of human speech (e.g., 100 Hz for males and 180 Hz for females). In some cases, the filtering may cut the audio content more at the fundamental frequencies of human speech. Filtering the audio content to reduce volume in frequencies corresponding to human speech may improve the speech-to-noise ratio in the given environment. 
     Filtering of frequencies in the audio content corresponding to human speech may reduce overall perceived loudness of the audio content. In some cases, the playback devices may offset this decrease in overall loudness by boosting frequencies above and/or below the frequencies in the audio content corresponding to human speech (e.g., bass and treble frequencies). In some cases, the playback device may use an equal loudness matching algorithm to boost frequencies by specific amounts to offset cutting of the frequencies in the audio content corresponding to human speech. Alternatively, overall gain of the audio content may be increased to offset the filtering of frequencies in the audio content corresponding to human speech. 
     The playback device may continue to filter the audio content while the signal-to-noise ratio in the given environment is below the speech threshold, among other examples. For instance, if the event is a voice interaction with a voice service, the playback device may filter the audio content while a user is speaking a voice input and/or while playing back a spoken response from the voice service. As another example, if the event is a phone call, the playback device may filter the audio content until the phone call ends (e.g., until the parties hang up). 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 while playing back first audio in a given environment at a given loudness: (a) detecting that an event is anticipated in the given environment, wherein the event involves playback of second audio and (b) determining a loudness of background noise in the given environment, wherein the background noise comprises ambient noise in the given environment; ducking the first audio in proportion to a difference between the given loudness of the first audio and the determined loudness of the background noise; and playing back the ducked first audio concurrently with the second audio. 
     (Feature 2) The method of feature 1, wherein playing back the ducked first audio concurrently with the second audio comprises determining that a difference between a loudness of the ducked first audio and a given dynamic range is (a) less than the determined loudness of the background noise or (b) greater than the determined loudness of the background noise; when the determined difference between the loudness of the ducked first audio and the given dynamic range is less than the determined loudness of the background noise, compressing the first audio to a dynamic range that is louder than the determined loudness of the background noise and playing back the compressed first audio; and when the determined difference between the loudness of the ducked first audio and the given dynamic range is greater than the determined loudness of the background noise, playing back the first audio without compression. 
     (Feature 3) The method of feature 1, wherein detecting that the event is anticipated in the given environment comprises receiving an indication that a voice command within the given environment is anticipated. 
     (Feature 4) The method of feature 3, wherein receiving the indication that the voice command within the given environment is anticipated comprises detecting, via one or more microphones, a voice input comprising a wake-word. 
     (Feature 5) The method of feature 3, wherein the first audio comprises one or more audio tracks, wherein the second audio comprises a spoken response to the voice command received from a voice service, and wherein playing back the ducked first audio concurrently with the second audio comprises playing back the one or more audio tracks concurrently with the spoken response to the voice command. 
     (Feature 6) The method of feature 3, wherein playing back the ducked first audio concurrently with the second audio comprises detecting that a signal-to-noise ratio within the given environment is below a voice input threshold; and responsively, filtering the first audio, wherein filtering the first audio comprises cutting the first audio in a frequency range corresponding to human speech. 
     (Feature 7) The method of feature 1, wherein filtering the first audio further comprises boosting the first audio outside the frequency range corresponding to human speech. 
     (Feature 8) The method of feature 1, wherein the playback device is a first playback device of a group of playback device that includes one or more second playback devices, and wherein playing back the ducked first audio concurrently with the second audio comprises playing back the ducked first audio concurrently with the second audio in synchrony with the one or more second playback devices. 
     (Feature 9) The method of feature 1, wherein determining the loudness of background noise in the given environment comprises measuring the loudness of the background noise in the given environment via one or more microphone. 
     (Feature 10) The method of feature 9, wherein at least one of the one or more microphones is housed in a networked microphone device that is distinct from the playback device, and wherein measuring the loudness of the background noise in the given environment via one or more microphones comprises causing the networked microphone device to measure the loudness of the background noise in the given environment. 
     (Feature 11) The method of feature 9, wherein measuring the loudness of the background noise in the given environment comprises offsetting the first audio being played back by the playback device from the measurement of the background noise in the given environment. 
     (Feature 12) The method of feature 1, wherein the operations further comprise detecting that the event has completed, and wherein ducking the first audio comprises ducking the first audio until the event has completed. 
     (Feature 13) A tangible, non-transitory computer-readable medium having stored therein instructions executable by one or more processors to cause a device to perform the method of any of features 1-12. 
     (Feature 14) A playback device configured to perform the method of any of features 1-12. 
     (Feature 15) A media playback system configured to perform the method of any of features 1-12. 
     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.