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author | Heidi von Markham <hvm@google.com> | 2015-04-14 14:25:14 -0700 |
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committer | Heidi von Markham <hvm@google.com> | 2015-04-16 10:39:46 -0700 |
commit | 52c19b9c4ea200cda3ffb6bf257aa112f79d6b89 (patch) | |
tree | 02e4df47f38c2bdb44c1265cadb3dd0753d81b7b /src/devices | |
parent | 7f74d9704bab641c61db956209475db639f3608a (diff) | |
download | source.android.com-52c19b9c4ea200cda3ffb6bf257aa112f79d6b89.tar.gz |
Docs: Basic edits, 80 char column, consistent phrasing
Adding feedback
Bug: 18947865
Change-Id: Ie0538c3fc9e2f672bc5b4ce5560cdee774dc65d2
Diffstat (limited to 'src/devices')
-rw-r--r-- | src/devices/audio/terminology.jd | 606 |
1 files changed, 281 insertions, 325 deletions
diff --git a/src/devices/audio/terminology.jd b/src/devices/audio/terminology.jd index 8a4ce600..cec0bcdf 100644 --- a/src/devices/audio/terminology.jd +++ b/src/devices/audio/terminology.jd @@ -2,7 +2,7 @@ page.title=Audio Terminology @jd:body <!-- - Copyright 2014 The Android Open Source Project + Copyright 2015 The Android Open Source Project Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. @@ -25,42 +25,44 @@ page.title=Audio Terminology </div> <p> -This document provides a glossary of audio-related terminology, including -a list of widely used, generic terms and a list of terms that are specific -to Android. +This glossary of audio-related terminology includes widely-used generic terms +and Android-specific terms. </p> <h2 id="genericTerm">Generic Terms</h2> <p> -These are audio terms that are widely used, with their conventional meanings. +Generic audio-related terms have conventional meanings. </p> <h3 id="digitalAudioTerms">Digital Audio</h3> +<p> +Digital audio terms relate to handling sound using audio signals encoded +in digital form. For details, refer to +<a href="http://en.wikipedia.org/wiki/Digital_audio">Digital Audio</a>. +</p> <dl> <dt>acoustics</dt> <dd> -The study of the mechanical properties of sound, for example how the -physical placement of transducers such as speakers and microphones on -a device affects perceived audio quality. +Study of the mechanical properties of sound, such as how the physical +placement of transducers (speakers, microphones, etc.) on a device affects +perceived audio quality. </dd> <dt>attenuation</dt> <dd> -A multiplicative factor less than or equal to 1.0, -applied to an audio signal to decrease the signal level. -Compare to "gain." +Multiplicative factor less than or equal to 1.0, applied to an audio signal +to decrease the signal level. Compare to <em>gain</em>. </dd> <dt>audiophile</dt> <dd> -An <a href="http://en.wikipedia.org/wiki/Audiophile">audiophile</a> -is an individual who is concerned with a superior music -reproduction experience, especially someone willing to make tradeoffs -(of expense, component size, room design, etc.) beyond what an ordinary -person might choose. +Person concerned with a superior music reproduction experience, especially +willing to make substantial tradeoffs (expense, component size, room design, +etc.) for sound quality. For details, refer to +<a href="http://en.wikipedia.org/wiki/Audiophile">audiophile</a>. </dd> <dt>bits per sample or bit depth</dt> @@ -70,90 +72,84 @@ Number of bits of information per sample. <dt>channel</dt> <dd> -A single stream of audio information, usually corresponding to one -location of recording or playback. +Single stream of audio information, usually corresponding to one location of +recording or playback. </dd> <dt>downmixing</dt> <dd> -To decrease the number of channels, e.g. from stereo to mono, or from 5.1 to stereo. -This can be accomplished by dropping some channels, mixing channels, or more advanced signal processing. -Simple mixing without attenuation or limiting has the potential for overflow and clipping. -Compare to "upmixing." +Decrease the number of channels, such as from stereo to mono or from 5.1 to +stereo. Accomplished by dropping channels, mixing channels, or more advanced +signal processing. Simple mixing without attenuation or limiting has the +potential for overflow and clipping. Compare to <em>upmixing</em>. </dd> <dt>DSD</dt> <dd> -Direct Stream Digital, a proprietary audio encoding based on -<a href="http://en.wikipedia.org/wiki/Pulse-density_modulation">pulse-density modulation</a>. -Whereas PCM encodes a waveform as a sequence of individual audio samples of multiple bits, -DSD encodes a waveform as a sequence of bits at a very high sample rate. -For DSD, there is no concept of "samples" in the conventional PCM sense. -Both PCM and DSD represent multiple channels by independent sequences. -DSD is better suited to content distribution than as an internal representation for processing, -as it can be difficult to apply traditional DSP algorithms to DSD. -DSD is used in -<a href="http://en.wikipedia.org/wiki/Super_Audio_CD">Super Audio CD</a> -(SACD) and in DSD over PCM (DoP) for USB. -See the Wikipedia article -<a href="http://en.wikipedia.org/wiki/Direct_Stream_Digital">Digital Stream Digital</a> -for more information. +Direct Stream Digital. Proprietary audio encoding based on +<a href="http://en.wikipedia.org/wiki/Pulse-density_modulation">pulse-density +modulation</a>. While Pulse Code Modulation (PCM) encodes a waveform as a +sequence of individual audio samples of multiple bits, DSD encodes a waveform as +a sequence of bits at a very high sample rate (without the concept of samples). +Both PCM and DSD represent multiple channels by independent sequences. DSD is +better suited to content distribution than as an internal representation for +processing as it can be difficult to apply traditional digital signal processing +(DSP) algorithms to DSD. DSD is used in <a href="http://en.wikipedia.org/wiki/Super_Audio_CD">Super Audio CD (SACD)</a> and in DSD over PCM (DoP) for USB. For details, refer +to <a href="http://en.wikipedia.org/wiki/Direct_Stream_Digital">Digital Stream +Digital</a>. </dd> <dt>duck</dt> <dd> -To temporarily reduce the volume of one stream, when another stream -becomes active. For example, if music is playing and a notification arrives, -then the music stream could be ducked while the notification plays. -Compare to "mute." +Temporarily reduce the volume of a stream when another stream becomes active. +For example, if music is playing when a notification arrives, the music ducks +while the notification plays. Compare to <em>mute</em>. </dd> <dt>FIFO</dt> <dd> -A hardware module or software data structure that implements +First In, First Out. Hardware module or software data structure that implements <a href="http://en.wikipedia.org/wiki/FIFO">First In, First Out</a> -queueing of data. In the context of audio, the data stored in the queue -are typically audio frames. A FIFO can be implemented by a +queueing of data. In an audio context, the data stored in the queue are +typically audio frames. FIFO can be implemented by a <a href="http://en.wikipedia.org/wiki/Circular_buffer">circular buffer</a>. </dd> <dt>frame</dt> <dd> -A set of samples, one per channel, at a point in time. +Set of samples, one per channel, at a point in time. </dd> <dt>frames per buffer</dt> <dd> -The number of frames handed from one module to the next at once; -for example the audio HAL interface uses this concept. +Number of frames handed from one module to the next at one time. The audio HAL +interface uses the concept of frames per buffer. </dd> <dt>gain</dt> <dd> -A multiplicative factor greater than or equal to 1.0, -applied to an audio signal to increase the signal level. -Compare to "attenuation." +Multiplicative factor greater than or equal to 1.0, applied to an audio signal +to increase the signal level. Compare to <em>attenuation</em>. </dd> <dt>HD audio</dt> <dd> -High-Definition audio, a synonym for "high-resolution audio." -Not to be confused with Intel High Definition Audio. +High-Definition audio. Synonym for high-resolution audio (but different than +Intel High Definition Audio). </dd> <dt>Hz</dt> <dd> -The units for sample rate or frame rate. +Units for sample rate or frame rate. </dd> <dt>high-resolution audio</dt> <dd> -There is no standard definition, but high-resolution usually means any representation -with greater bit-depth and sample rate than CDs (which are stereo 16-bit PCM at 44.1 kHz), -and with no lossy data compression applied. -Equivalent to "HD audio." See the Wikipedia article -<a href="http://en.wikipedia.org/wiki/High-resolution_audio">high-resolution audio</a> -for more information. +Representation with greater bit-depth and sample rate than CDs (stereo 16-bit +PCM at 44.1 kHz) and without lossy data compression. Equivalent to HD audio. +For details, refer to +<a href="http://en.wikipedia.org/wiki/High-resolution_audio">high-resolution +audio</a>. </dd> <dt>latency</dt> @@ -163,28 +159,28 @@ Time delay as a signal passes through a system. <dt>lossless</dt> <dd> -A <a href="http://en.wikipedia.org/wiki/Lossless_compression">lossless data compression</a> -algorithm preserves bit accuracy across encoding and decoding. -The result of decoding any previously encoded data is equivalent to the original data. -Examples of lossless audio content distribution formats include -<a href="http://en.wikipedia.org/wiki/Compact_disc">CDs</a>, PCM within +A <a href="http://en.wikipedia.org/wiki/Lossless_compression">lossless data +compression algorithm</a> that preserves bit accuracy across encoding and +decoding, where the result of decoding previously encoded data is equivalent +to the original data. Examples of lossless audio content distribution formats +include <a href="http://en.wikipedia.org/wiki/Compact_disc">CDs</a>, PCM within <a href="http://en.wikipedia.org/wiki/WAV">WAV</a>, and <a href="http://en.wikipedia.org/wiki/FLAC">FLAC</a>. -Note that the authoring process may reduce the bit depth or sample rate from that of the -<a href="http://en.wikipedia.org/wiki/Audio_mastering">masters</a>. -Distribution formats that preserve the resolution and bit accuracy of masters -are the subject of "high-resolution audio." +The authoring process may reduce the bit depth or sample rate from that of the +<a href="http://en.wikipedia.org/wiki/Audio_mastering">masters</a>; distribution +formats that preserve the resolution and bit accuracy of masters are the subject +of high-resolution audio. </dd> <dt>lossy</dt> <dd> -A <a href="http://en.wikipedia.org/wiki/Lossy_compression">lossy data compression</a> -algorithm attempts to preserve the most important features of media across -encoding and decoding. The result of decoding any previously encoded -data is perceptually similar to the original data, but it is not identical. -Examples of lossy audio compression algorithms include MP3 and AAC. -As analog values are from a continuous domain, whereas digital values are discrete, -ADC and DAC are lossy conversions with respect to amplitude. See also "transparency." +A <a href="http://en.wikipedia.org/wiki/Lossy_compression">lossy data +compression algorithm</a> that attempts to preserve the most important features +of media across encoding and decoding where the result of decoding previously +encoded data is perceptually similar to the original data but not identical. +Examples of lossy audio compression algorithms include MP3 and AAC. As analog +values are from a continuous domain and digital values are discrete, ADC and DAC +are lossy conversions with respect to amplitude. See also <em>transparency</em>. </dd> <dt>mono</dt> @@ -194,61 +190,60 @@ One channel. <dt>multichannel</dt> <dd> -See "surround sound." -Strictly, since stereo is more than one channel, it is also "multi" channel. -But that usage would be confusing. +See <em>surround sound</em>. In strict terms, <em>stereo</em> is more than one +channel and could be considered multichannel; however, such usage is confusing +and thus avoided. </dd> <dt>mute</dt> <dd> -To (temporarily) force volume to be zero, independently from the usual volume controls. +Temporarily force volume to be zero, independent from the usual volume controls. </dd> <dt>overrun</dt> <dd> -An audible <a href="http://en.wikipedia.org/wiki/Glitch">glitch</a> caused by failure -to accept supplied data in sufficient time. -See Wikipedia article <a href="http://en.wikipedia.org/wiki/Buffer_underrun">buffer underrun</a> -[sic; the article for "buffer overrun" describes an unrelated failure]. -Compare to "underrun." +Audible <a href="http://en.wikipedia.org/wiki/Glitch">glitch</a> caused by +failure to accept supplied data in sufficient time. For details, refer to +<a href="http://en.wikipedia.org/wiki/Buffer_underrun">buffer underrun</a>. +Compare to <em>underrun</em>. </dd> <dt>panning</dt> <dd> -To direct a signal to a desired position within a stereo or multi-channel field. +Direct a signal to a desired position within a stereo or multichannel field. </dd> <dt>PCM</dt> <dd> -Pulse Code Modulation, the most common low-level encoding of digital audio. -The audio signal is sampled at a regular interval, called the sample rate, -and then quantized to discrete values within a particular range depending on the bit depth. -For example, for 16-bit PCM, the sample values are integers between -32768 and +32767. +Pulse Code Modulation. Most common low-level encoding of digital audio. The +audio signal is sampled at a regular interval, called the sample rate, then +quantized to discrete values within a particular range depending on the bit +depth. For example, for 16-bit PCM the sample values are integers between +-32768 and +32767. </dd> <dt>ramp</dt> <dd> -To gradually increase or decrease the level of a particular audio parameter, -for example volume or the strength of an effect. -A volume ramp is commonly applied when pausing and resuming music, to avoid a hard audible transition. +Gradually increase or decrease the level of a particular audio parameter, such +as the volume or the strength of an effect. A volume ramp is commonly applied +when pausing and resuming music to avoid a hard audible transition. </dd> <dt>sample</dt> <dd> -A number representing the audio value for a single channel at a point in time. +Number representing the audio value for a single channel at a point in time. </dd> <dt>sample rate or frame rate</dt> <dd> -Number of frames per second; -note that "frame rate" is thus more accurate, -but "sample rate" is conventionally used to mean "frame rate." +Number of frames per second. While <em>frame rate</em> is more accurate, +<em>sample rate</em> is conventionally used to mean frame rate. </dd> <dt>sonification</dt> <dd> -The use of sound to express feedback or information, -for example touch sounds and keyboard sounds. +Use of sound to express feedback or information, such as touch sounds and +keyboard sounds. </dd> <dt>stereo</dt> @@ -258,43 +253,45 @@ Two channels. <dt>stereo widening</dt> <dd> -An effect applied to a stereo signal, to make another stereo signal which sounds fuller and richer. -The effect can also be applied to a mono signal, in which case it is a type of upmixing. +Effect applied to a stereo signal to make another stereo signal that sounds +fuller and richer. The effect can also be applied to a mono signal, where it is +a type of upmixing. </dd> <dt>surround sound</dt> <dd> -Various techniques for increasing the ability of a listener to perceive -sound position beyond stereo left and right. +Techniques for increasing the ability of a listener to perceive sound position +beyond stereo left and right. </dd> <dt>transparency</dt> <dd> -The ideal result of lossy data compression, as stated in the -<a href="http://en.wikipedia.org/wiki/Transparency_%28data_compression%29">Transparency</a> Wikipedia article. -A lossy data conversion is said to be transparent if it is perceptually indistinguishable from the -original by a human subject. +Ideal result of lossy data compression. Lossy data conversion is transparent if +it is perceptually indistinguishable from the original by a human subject. For +details, refer to +<a href="http://en.wikipedia.org/wiki/Transparency_%28data_compression%29">Transparency</a>. + </dd> <dt>underrun</dt> <dd> -An audible <a href="http://en.wikipedia.org/wiki/Glitch">glitch</a> caused by failure -to supply needed data in sufficient time. -See Wikipedia article <a href="http://en.wikipedia.org/wiki/Buffer_underrun">buffer underrun</a>. -Compare to "overrun." +Audible <a href="http://en.wikipedia.org/wiki/Glitch">glitch</a> caused by +failure to supply needed data in sufficient time. For details, refer to +<a href="http://en.wikipedia.org/wiki/Buffer_underrun">buffer underrun</a>. +Compare to <em>overrun</em>. </dd> <dt>upmixing</dt> <dd> -To increase the number of channels, e.g. from mono to stereo, or from stereo to surround sound. -This can be accomplished by duplication, panning, or more advanced signal processing. -Compare to "downmixing." +Increase the number of channels, such as from mono to stereo or from stereo to +surround sound. Accomplished by duplication, panning, or more advanced signal +processing. Compare to <em>downmixing</em>. </dd> <dt>virtualizer</dt> <dd> -An effect that attempts to spatialize audio channels, such as trying to -simulate more speakers, or give the illusion that various sound sources have position. +Effect that attempts to spatialize audio channels, such as trying to simulate +more speakers or give the illusion that sound sources have position. </dd> <dt>volume</dt> @@ -304,113 +301,90 @@ Loudness, the subjective strength of an audio signal. </dl> -<h3 id="hardwareTerms">Hardware and Accessories</h3> +<h3 id="interDeviceTerms">Inter-device interconnect</h3> <p> -These terms are related to audio hardware and accessories. -</p> - -<h4 id="interDeviceTerms">Inter-device interconnect</h4> - -<p> -These technologies connect audio and video components between devices, -and are readily visible at the external connectors. The HAL implementor -may need to be aware of these, as well as the end user. +Inter-device interconnection technologies connect audio and video components +between devices and are readily visible at the external connectors. The HAL +implementer and end user should be aware of these terms. </p> <dl> <dt>Bluetooth</dt> <dd> -A short range wireless technology. -The major audio-related +Short range wireless technology. For details on the audio-related <a href="http://en.wikipedia.org/wiki/Bluetooth_profile">Bluetooth profiles</a> and -<a href="http://en.wikipedia.org/wiki/Bluetooth_protocols">Bluetooth protocols</a> -are described at these Wikipedia articles: - -<ul> - -<li><a href="http://en.wikipedia.org/wiki/Bluetooth_profile#Advanced_Audio_Distribution_Profile_.28A2DP.29">A2DP</a> -for music -</li> - -<li><a href="http://en.wikipedia.org/wiki/Bluetooth_protocols#Synchronous_connection-oriented_.28SCO.29_link">SCO</a> -for telephony -</li> - -<li><a href="http://en.wikipedia.org/wiki/List_of_Bluetooth_profiles#Audio.2FVideo_Remote_Control_Profile_.28AVRCP.29">Audio/Video Remote Control Profile (AVRCP)</a> -</li> - -</ul> - +<a href="http://en.wikipedia.org/wiki/Bluetooth_protocols">Bluetooth protocols</a>, +refer to <a href="http://en.wikipedia.org/wiki/Bluetooth_profile#Advanced_Audio_Distribution_Profile_.28A2DP.29">A2DP</a> for +music, <a href="http://en.wikipedia.org/wiki/Bluetooth_protocols#Synchronous_connection-oriented_.28SCO.29_link">SCO</a> for telephony, and <a href="http://en.wikipedia.org/wiki/List_of_Bluetooth_profiles#Audio.2FVideo_Remote_Control_Profile_.28AVRCP.29">Audio/Video Remote Control Profile (AVRCP)</a>. </dd> <dt>DisplayPort</dt> <dd> -Digital display interface by VESA. +Digital display interface by the Video Electronics Standards Association (VESA). </dd> <dt>HDMI</dt> <dd> -High-Definition Multimedia Interface, an interface for transferring -audio and video data. For mobile devices, either a micro-HDMI (type D) or MHL connector is used. +High-Definition Multimedia Interface. Interface for transferring audio and +video data. For mobile devices, a micro-HDMI (type D) or MHL connector is used. </dd> <dt>Intel HDA</dt> <dd> -<a href="http://en.wikipedia.org/wiki/Intel_High_Definition_Audio">Intel High Definition Audio</a> -(commonly shortened to HDA) is a specification for, among other things, a front-panel connector. -Not to be confused with generic "high-definition audio" or "high-resolution audio." +Intel High Definition Audio (do not confuse with generic <em>high-definition +audio</em> or <em>high-resolution audio</em>). Specification for a front-panel +connector. For details, refer to +<a href="http://en.wikipedia.org/wiki/Intel_High_Definition_Audio">Intel High +Definition Audio</a>. </dd> <dt>MHL</dt> <dd> -Mobile High-Definition Link is a mobile audio/video interface, often -over micro-USB connector. +Mobile High-Definition Link. Mobile audio/video interface, often over micro-USB +connector. </dd> <dt>phone connector</dt> <dd> -A mini or sub-mini phone connector -connects a device to wired headphones, headset, or line-level amplifier. +Mini or sub-mini component that connects a device to wired headphones, headset, +or line-level amplifier. </dd> <dt>SlimPort</dt> <dd> -An adapter from micro-USB to HDMI. +Adapter from micro-USB to HDMI. </dd> <dt>S/PDIF</dt> <dd> -Sony/Philips Digital Interface Format is an interconnect for uncompressed PCM. -See Wikipedia article <a href="http://en.wikipedia.org/wiki/S/PDIF">S/PDIF</a>. +Sony/Philips Digital Interface Format. Interconnect for uncompressed PCM. For +details, refer to <a href="http://en.wikipedia.org/wiki/S/PDIF">S/PDIF</a>. </dd> <dt>Thunderbolt</dt> <dd> -<a href="http://en.wikipedia.org/wiki/Thunderbolt_%28interface%29">Thunderbolt</a> -is a multimedia interface that competes with USB and HDMI for connecting to high-end peripherals. +Multimedia interface that competes with USB and HDMI for connecting to high-end +peripherals. For details, refer to <a href="http://en.wikipedia.org/wiki/Thunderbolt_%28interface%29">Thunderbolt</a>. </dd> <dt>USB</dt> <dd> -Universal Serial Bus. -See Wikipedia article <a href="http://en.wikipedia.org/wiki/USB">USB</a>. +Universal Serial Bus. For details, refer to +<a href="http://en.wikipedia.org/wiki/USB">USB</a>. </dd> </dl> -<h4 id="intraDeviceTerms">Intra-device interconnect</h4> +<h3 id="intraDeviceTerms">Intra-device interconnect</h3> <p> -These technologies connect internal audio components within a given -device, and are not visible without disassembling the device. The HAL -implementor may need to be aware of these, but not the end user. -</p> - -<p> -See these Wikipedia articles: +Intra-device interconnection technologies connect internal audio components +within a given device and are not visible without disassembling the device. The +HAL implementer may need to be aware of these, but not the end user. For details +on intra-device interconnections, refer to the following articles: </p> <ul> <li><a href="http://en.wikipedia.org/wiki/General-purpose_input/output">GPIO</a></li> @@ -424,304 +398,289 @@ See these Wikipedia articles: <h3 id="signalTerms">Audio Signal Path</h3> <p> -These terms are related to the signal path that audio data follows from -an application to the transducer, or vice-versa. +Audio signal path terms relate to the signal path that audio data follows from +an application to the transducer or vice-versa. </p> <dl> <dt>ADC</dt> <dd> -Analog to digital converter, a module that converts an analog signal -(continuous in both time and amplitude) to a digital signal (discrete in -both time and amplitude). Conceptually, an ADC consists of a periodic -sample-and-hold followed by a quantizer, although it does not have to -be implemented that way. An ADC is usually preceded by a low-pass filter -to remove any high frequency components that are not representable using -the desired sample rate. See Wikipedia article -<a href="http://en.wikipedia.org/wiki/Analog-to-digital_converter">Analog-to-digital converter</a>. +Analog-to-digital converter. Module that converts an analog signal (continuous +in time and amplitude) to a digital signal (discrete in time and amplitude). +Conceptually, an ADC consists of a periodic sample-and-hold followed by a +quantizer, although it does not have to be implemented that way. An ADC is +usually preceded by a low-pass filter to remove any high frequency components +that are not representable using the desired sample rate. For details, refer to +<a href="http://en.wikipedia.org/wiki/Analog-to-digital_converter">Analog-to-digital +converter</a>. </dd> <dt>AP</dt> <dd> -Application processor, the main general-purpose computer on a mobile device. +Application processor. Main general-purpose computer on a mobile device. </dd> <dt>codec</dt> <dd> -Coder-decoder, a module that encodes and/or decodes an audio signal -from one representation to another. Typically this is analog to PCM, or PCM to analog. -Strictly, the term "codec" is reserved for modules that both encode and decode, -however it can also more loosely refer to only one of these. -See Wikipedia article +Coder-decoder. Module that encodes and/or decodes an audio signal from one +representation to another (typically analog to PCM or PCM to analog). In strict +terms, <em>codec</em> is reserved for modules that both encode and decode but +can be used loosely to refer to only one of these. For details, refer to <a href="http://en.wikipedia.org/wiki/Audio_codec">Audio codec</a>. </dd> <dt>DAC</dt> <dd> -Digital to analog converter, a module that converts a digital signal -(discrete in both time and amplitude) to an analog signal -(continuous in both time and amplitude). A DAC is usually followed by -a low-pass filter to remove any high frequency components introduced -by digital quantization. -See Wikipedia article -<a href="http://en.wikipedia.org/wiki/Digital-to-analog_converter">Digital-to-analog converter</a>. +Digital-to-analog converter. Module that converts a digital signal (discrete in +time and amplitude) to an analog signal (continuous in time and amplitude). +Often followed by a low-pass filter to remove high-frequency components +introduced by digital quantization. For details, refer to +<a href="http://en.wikipedia.org/wiki/Digital-to-analog_converter">Digital-to-analog +converter</a>. </dd> <dt>DSP</dt> <dd> -Digital Signal Processor, an optional component which is typically located -after the application processor (for output), or before the application processor (for input). -The primary purpose of a DSP is to off-load the application processor, -and provide signal processing features at a lower power cost. +Digital Signal Processor. Optional component typically located after the +application processor (for output) or before the application processor (for +input). Primary purpose is to off-load the application processor and provide +signal processing features at a lower power cost. </dd> <dt>PDM</dt> <dd> -Pulse-density modulation -is a form of modulation used to represent an analog signal by a digital signal, -where the relative density of 1s versus 0s indicates the signal level. -It is commonly used by digital to analog converters. -See Wikipedia article -<a href="http://en.wikipedia.org/wiki/Pulse-density_modulation">Pulse-density modulation</a>. +Pulse-density modulation. Form of modulation used to represent an analog signal +by a digital signal, where the relative density of 1s versus 0s indicates the +signal level. Commonly used by digital to analog converters. For details, refer +to <a href="http://en.wikipedia.org/wiki/Pulse-density_modulation">Pulse-density +modulation</a>. </dd> <dt>PWM</dt> <dd> -Pulse-width modulation -is a form of modulation used to represent an analog signal by a digital signal, -where the relative width of a digital pulse indicates the signal level. -It is commonly used by analog to digital converters. -See Wikipedia article -<a href="http://en.wikipedia.org/wiki/Pulse-width_modulation">Pulse-width modulation</a>. +Pulse-width modulation. Form of modulation used to represent an analog signal by +a digital signal, where the relative width of a digital pulse indicates the +signal level. Commonly used by analog-to-digital converters. For details, refer +to <a href="http://en.wikipedia.org/wiki/Pulse-width_modulation">Pulse-width +modulation</a>. </dd> <dt>transducer</dt> <dd> -A transducer converts variations in physical "real-world" quantities to electrical signals. -In audio, the physical quantity is sound pressure, -and the transducers are the loudspeaker and microphone. -See Wikipedia article +Converts variations in physical real-world quantities to electrical signals. In +audio, the physical quantity is sound pressure, and the transducers are the +loudspeaker and microphone. For details, refer to <a href="http://en.wikipedia.org/wiki/Transducer">Transducer</a>. </dd> </dl> <h3 id="srcTerms">Sample Rate Conversion</h3> +<p> +Sample rate conversion terms relate to the process of converting from one +sampling rate to another. +</p> <dl> <dt>downsample</dt> -<dd>To resample, where sink sample rate < source sample rate.</dd> +<dd>Resample, where sink sample rate < source sample rate.</dd> <dt>Nyquist frequency</dt> <dd> -The Nyquist frequency, equal to 1/2 of a given sample rate, is the -maximum frequency component that can be represented by a discretized -signal at that sample rate. For example, the human hearing range is -typically assumed to extend up to approximately 20 kHz, and so a digital -audio signal must have a sample rate of at least 40 kHz to represent that -range. In practice, sample rates of 44.1 kHz and 48 kHz are commonly -used, with Nyquist frequencies of 22.05 kHz and 24 kHz respectively. -See +Maximum frequency component that can be represented by a discretized signal at +1/2 of a given sample rate. For example, the human hearing range extends to +approximately 20 kHz, so a digital audio signal must have a sample rate of at +least 40 kHz to represent that range. In practice, sample rates of 44.1 kHz and +48 kHz are commonly used, with Nyquist frequencies of 22.05 kHz and 24 kHz +respectively. For details, refer to <a href="http://en.wikipedia.org/wiki/Nyquist_frequency">Nyquist frequency</a> and -<a href="http://en.wikipedia.org/wiki/Hearing_range">Hearing range</a> -for more information. +<a href="http://en.wikipedia.org/wiki/Hearing_range">Hearing range</a>. </dd> <dt>resampler</dt> <dd>Synonym for sample rate converter.</dd> <dt>resampling</dt> -<dd>The process of converting sample rate.</dd> +<dd>Process of converting sample rate.</dd> <dt>sample rate converter</dt> -<dd>A module that resamples.</dd> +<dd>Module that resamples.</dd> <dt>sink</dt> -<dd>The output of a resampler.</dd> +<dd>Output of a resampler.</dd> <dt>source</dt> -<dd>The input to a resampler.</dd> +<dd>Input to a resampler.</dd> <dt>upsample</dt> -<dd>To resample, where sink sample rate > source sample rate.</dd> +<dd>Resample, where sink sample rate > source sample rate.</dd> </dl> <h2 id="androidSpecificTerms">Android-Specific Terms</h2> <p> -These are terms specific to the Android audio framework, or that -may have a special meaning within Android beyond their general meaning. +Android-specific terms include terms used only in the Android audio framework +and generic terms that have special meaning within Android. </p> <dl> <dt>ALSA</dt> <dd> -Advanced Linux Sound Architecture. As the name suggests, it is an audio -framework primarily for Linux, but it has influenced other systems. -See Wikipedia article -<a href="http://en.wikipedia.org/wiki/Advanced_Linux_Sound_Architecture">ALSA</a> -for the general definition. As used within Android, it refers primarily -to the kernel audio framework and drivers, not to the user-mode API. See -tinyalsa. +Advanced Linux Sound Architecture. An audio framework for Linux that has also +influenced other systems. For a generic definition, refer to +<a href="http://en.wikipedia.org/wiki/Advanced_Linux_Sound_Architecture">ALSA</a>. +In Android, ALSA refers to the kernel audio framework and drivers and not to the +user-mode API. See also <em>tinyalsa</em>. </dd> <dt>audio device</dt> <dd> -Any audio I/O end-point that is backed by a HAL implementation. +Audio I/O endpoint backed by a HAL implementation. </dd> <dt>AudioEffect</dt> <dd> -An API and implementation framework for output (post-processing) effects -and input (pre-processing) effects. The API is defined at +API and implementation framework for output (post-processing) effects and input +(pre-processing) effects. The API is defined at <a href="http://developer.android.com/reference/android/media/audiofx/AudioEffect.html">android.media.audiofx.AudioEffect</a>. </dd> <dt>AudioFlinger</dt> <dd> -The sound server implementation for Android. AudioFlinger -runs within the mediaserver process. See Wikipedia article -<a href="http://en.wikipedia.org/wiki/Sound_server">Sound server</a> -for the generic definition. +Android sound server implementation. AudioFlinger runs within the mediaserver +process. For a generic definition, refer to +<a href="http://en.wikipedia.org/wiki/Sound_server">Sound server</a>. </dd> <dt>audio focus</dt> <dd> -A set of APIs for managing audio interactions across multiple independent apps. -See <a href="http://developer.android.com/training/managing-audio/audio-focus.html">Managing Audio -Focus</a> and the focus-related methods and constants of +Set of APIs for managing audio interactions across multiple independent apps. +For details, see <a href="http://developer.android.com/training/managing-audio/audio-focus.html">Managing Audio Focus</a> and the focus-related methods and constants of <a href="http://developer.android.com/reference/android/media/AudioManager.html">android.media.AudioManager</a>. </dd> <dt>AudioMixer</dt> <dd> -The module within AudioFlinger responsible for -combining multiple tracks and applying attenuation -(volume) and certain effects. The Wikipedia article -<a href="http://en.wikipedia.org/wiki/Audio_mixing_(recorded_music)">Audio mixing (recorded music)</a> -may be useful for understanding the generic -concept. But that article describes a mixer more as a hardware device -or a software application, rather than a software module within a system. +Module in AudioFlinger responsible for combining multiple tracks and applying +attenuation (volume) and effects. For a generic definition, refer to +<a href="http://en.wikipedia.org/wiki/Audio_mixing_(recorded_music)">Audio mixing (recorded music)</a> (discusses a mixer as a hardware device or software application, rather +than a software module within a system). </dd> <dt>audio policy</dt> <dd> -Service responsible for all actions that require a policy decision -to be made first, such as opening a new I/O stream, re-routing after a -change, and stream volume management. +Service responsible for all actions that require a policy decision to be made +first, such as opening a new I/O stream, re-routing after a change, and stream +volume management. </dd> <dt>AudioRecord</dt> <dd> -The primary low-level client API for receiving data from an audio -input device such as microphone. The data is usually in pulse-code modulation -(PCM) format. -The API is defined at +Primary low-level client API for receiving data from an audio input device such +as a microphone. The data is usually PCM format. The API is defined at <a href="http://developer.android.com/reference/android/media/AudioRecord.html">android.media.AudioRecord</a>. </dd> <dt>AudioResampler</dt> <dd> -The module within AudioFlinger responsible for -<a href="src.html">sample rate conversion</a>. +Module in AudioFlinger responsible for <a href="src.html">sample rate conversion</a>. </dd> <dt>audio source</dt> <dd> -An <a href="http://developer.android.com/reference/android/media/MediaRecorder.AudioSource.html">audio source</a> -is an enumeration of constants that indicates the desired use case for capturing audio input. -As of API level 21 and above, <a href="attributes.html">audio attributes</a> are preferred. +An enumeration of constants that indicates the desired use case for capturing +audio input. For details, see <a href="http://developer.android.com/reference/android/media/MediaRecorder.AudioSource.html">audio source</a>. As of API level 21 and above, +<a href="attributes.html">audio attributes</a> are preferred. </dd> <dt>AudioTrack</dt> <dd> -The primary low-level client API for sending data to an audio output -device such as a speaker. The data is usually in PCM format. -The API is defined at +Primary low-level client API for sending data to an audio output device such as +a speaker. The data is usually in PCM format. The API is defined at <a href="http://developer.android.com/reference/android/media/AudioTrack.html">android.media.AudioTrack</a>. </dd> <dt>audio_utils</dt> <dd> -An audio utility library for features such as PCM format conversion, WAV file I/O, and -<a href="avoiding_pi.html#nonBlockingAlgorithms">non-blocking FIFO</a>, -which is largely independent of the Android platform. +Audio utility library for features such as PCM format conversion, WAV file I/O, +and +<a href="avoiding_pi.html#nonBlockingAlgorithms">non-blocking FIFO</a>, which is +largely independent of the Android platform. </dd> <dt>client</dt> <dd> -Usually same as application or app, but sometimes the "client" of -AudioFlinger is actually a thread running within the mediaserver system -process. An example of that is when playing media that is decoded by a -MediaPlayer object. +Usually an application or app client. However, an AudioFlinger client can be a +thread running within the mediaserver system process, such as when playing media +decoded by a MediaPlayer object. </dd> <dt>HAL</dt> <dd> -Hardware Abstraction Layer. HAL is a generic term in Android. With -respect to audio, it is a layer between AudioFlinger and the kernel -device driver with a C API, which replaces the earlier C++ libaudio. +Hardware Abstraction Layer. HAL is a generic term in Android; in audio, it is a +layer between AudioFlinger and the kernel device driver with a C API (which +replaces the C++ libaudio). </dd> <dt>FastCapture</dt> <dd> -A thread within AudioFlinger that sends audio data to lower latency "fast tracks" +Thread within AudioFlinger that sends audio data to lower latency fast tracks and drives the input device when configured for reduced latency. </dd> <dt>FastMixer</dt> <dd> -A thread within AudioFlinger that receives and mixes audio data from lower latency "fast tracks" -and drives the primary output device when configured for reduced latency. +Thread within AudioFlinger that receives and mixes audio data from lower latency +fast tracks and drives the primary output device when configured for reduced +latency. </dd> <dt>fast track</dt> <dd> -An AudioTrack or AudioRecord client with lower latency but fewer features, on some devices and routes. +AudioTrack or AudioRecord client with lower latency but fewer features on some +devices and routes. </dd> <dt>MediaPlayer</dt> <dd> -A higher-level client API than AudioTrack, for playing either encoded -content, or content which includes multimedia audio and video tracks. +Higher-level client API than AudioTrack. Plays encoded content or content that +includes multimedia audio and video tracks. </dd> <dt>media.log</dt> <dd> -An AudioFlinger debugging feature, available in custom builds only, -for logging audio events to a circular buffer where they can then be -dumped retroactively when needed. +AudioFlinger debugging feature available in custom builds only. Used for logging +audio events to a circular buffer where they can then be retroactively dumped +when needed. </dd> <dt>mediaserver</dt> <dd> -An Android system process that contains a number of media-related -services, including AudioFlinger. +Android system process that contains media-related services, including +AudioFlinger. </dd> <dt>NBAIO</dt> <dd> -An abstraction for "non-blocking" audio input/output ports used within -AudioFlinger. The name can be misleading, as some implementations of -the NBAIO API actually do support blocking. The key implementations of -NBAIO are for pipes of various kinds. +Non-blocking audio input/output. Abstraction for AudioFlinger ports. The term +can be misleading as some implementations of the NBAIO API support blocking. The +key implementations of NBAIO are for different types of pipes. </dd> <dt>normal mixer</dt> <dd> -A thread within AudioFlinger that services most full-featured -AudioTrack clients, and either directly drives an output device or feeds -its sub-mix into FastMixer via a pipe. +Thread within AudioFlinger that services most full-featured AudioTrack clients. +Directly drives an output device or feeds its sub-mix into FastMixer via a pipe. </dd> <dt>OpenSL ES</dt> <dd> -An audio API standard by +Audio API standard by <a href="http://www.khronos.org/">The Khronos Group</a>. Android versions since API level 9 support a native audio API that is based on a subset of <a href="http://www.khronos.org/opensles/">OpenSL ES 1.0.1</a>. @@ -729,15 +688,14 @@ API level 9 support a native audio API that is based on a subset of <dt>silent mode</dt> <dd> -A user-settable feature to mute the phone ringer and notifications, -without affecting media playback (music, videos, games) or alarms. +User-settable feature to mute the phone ringer and notifications without +affecting media playback (music, videos, games) or alarms. </dd> <dt>SoundPool</dt> <dd> -A higher-level client API than AudioTrack, used for playing sampled -audio clips. It is useful for triggering UI feedback, game sounds, etc. -The API is defined at +Higher-level client API than AudioTrack. Plays sampled audio clips. Useful for +triggering UI feedback, game sounds, etc. The API is defined at <a href="http://developer.android.com/reference/android/media/SoundPool.html">android.media.SoundPool</a>. </dd> @@ -748,63 +706,61 @@ See <a href="{@docRoot}devices/media.html">Media</a>. <dt>StateQueue</dt> <dd> -A module within AudioFlinger responsible for synchronizing state -among threads. Whereas NBAIO is used to pass data, StateQueue is used -to pass control information. +Module within AudioFlinger responsible for synchronizing state among threads. +Whereas NBAIO is used to pass data, StateQueue is used to pass control +information. </dd> <dt>strategy</dt> <dd> -A grouping of stream types with similar behavior, used by the audio policy service. +Group of stream types with similar behavior. Used by the audio policy service. </dd> <dt>stream type</dt> <dd> -An enumeration that expresses a use case for audio output. -The audio policy implementation uses the stream type, along with other parameters, -to determine volume and routing decisions. -Specific stream types are listed at +Enumeration that expresses a use case for audio output. The audio policy +implementation uses the stream type, along with other parameters, to determine +volume and routing decisions. For a list of stream types, see <a href="http://developer.android.com/reference/android/media/AudioManager.html">android.media.AudioManager</a>. </dd> <dt>tee sink</dt> <dd> -See the separate article on tee sink in -<a href="debugging.html#teeSink">Audio Debugging</a>. +See <a href="debugging.html#teeSink">Audio Debugging</a>. </dd> <dt>tinyalsa</dt> <dd> -A small user-mode API above ALSA kernel with BSD license, recommended -for use in HAL implementations. +Small user-mode API above ALSA kernel with BSD license. Recommended for HAL +implementations. </dd> <dt>ToneGenerator</dt> <dd> -A higher-level client API than AudioTrack, used for playing DTMF signals. -See the Wikipedia article -<a href="http://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling">Dual-tone multi-frequency signaling</a>, -and the API definition at +Higher-level client API than AudioTrack. Plays dual-tone multi-frequency (DTMF) +signals. For details, refer to +<a href="http://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling">Dual-tone +multi-frequency signaling</a> and the API definition at <a href="http://developer.android.com/reference/android/media/ToneGenerator.html">android.media.ToneGenerator</a>. </dd> <dt>track</dt> <dd> -An audio stream, controlled by the AudioTrack or AudioRecord API. +Audio stream. Controlled by the AudioTrack or AudioRecord API. </dd> <dt>volume attenuation curve</dt> <dd> -A device-specific mapping from a generic volume index to a particular attenuation factor -for a given output. +Device-specific mapping from a generic volume index to a specific attenuation +factor for a given output. </dd> <dt>volume index</dt> <dd> -A unitless integer that expresses the desired relative volume of a stream. -The volume-related APIs of +Unitless integer that expresses the desired relative volume of a stream. The +volume-related APIs of <a href="http://developer.android.com/reference/android/media/AudioManager.html">android.media.AudioManager</a> operate in volume indices rather than absolute attenuation factors. </dd> -</dl> +</dl>
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