Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 1 | page.title=Audio Terminology |
| 2 | @jd:body |
| 3 | |
Clay Murphy | bc92aea | 2014-10-16 10:13:18 -0700 | [diff] [blame^] | 4 | <!-- |
| 5 | Copyright 2013 The Android Open Source Project |
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| 13 | Unless required by applicable law or agreed to in writing, software |
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Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 19 | <div id="qv-wrapper"> |
| 20 | <div id="qv"> |
| 21 | <h2>In this document</h2> |
| 22 | <ol id="auto-toc"> |
| 23 | </ol> |
| 24 | </div> |
| 25 | </div> |
| 26 | |
| 27 | <p> |
| 28 | This document provides a glossary of audio-related terminology, including |
| 29 | a list of widely used, generic terms and a list of terms that are specific |
| 30 | to Android. |
| 31 | </p> |
| 32 | |
| 33 | <h2 id="genericTerm">Generic Terms</h2> |
| 34 | |
| 35 | <p> |
| 36 | These are audio terms that are widely used, with their conventional meanings. |
| 37 | </p> |
| 38 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 39 | <h3 id="digitalAudioTerms">Digital Audio</h3> |
| 40 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 41 | <dl> |
| 42 | |
Glenn Kasten | 298f382 | 2013-06-12 17:17:36 -0700 | [diff] [blame] | 43 | <dt>acoustics</dt> |
| 44 | <dd> |
| 45 | The study of the mechanical properties of sound, for example how the |
| 46 | physical placement of transducers such as speakers and microphones on |
| 47 | a device affects perceived audio quality. |
| 48 | </dd> |
| 49 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 50 | <dt>attenuation</dt> |
| 51 | <dd> |
| 52 | A multiplicative factor less than or equal to 1.0, |
| 53 | applied to an audio signal to decrease the signal level. |
| 54 | Compare to "gain". |
| 55 | </dd> |
| 56 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 57 | <dt>bits per sample or bit depth</dt> |
| 58 | <dd> |
| 59 | Number of bits of information per sample. |
| 60 | </dd> |
| 61 | |
| 62 | <dt>channel</dt> |
| 63 | <dd> |
| 64 | A single stream of audio information, usually corresponding to one |
| 65 | location of recording or playback. |
| 66 | </dd> |
| 67 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 68 | <dt>downmixing</dt> |
| 69 | <dd> |
| 70 | To decrease the number of channels, e.g. from stereo to mono, or from 5.1 to stereo. |
| 71 | This can be accomplished by dropping some channels, mixing channels, or more advanced signal processing. |
| 72 | Simple mixing without attenuation or limiting has the potential for overflow and clipping. |
| 73 | Compare to "upmixing". |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 74 | </dd> |
| 75 | |
| 76 | <dt>duck</dt> |
| 77 | <dd> |
| 78 | To temporarily reduce the volume of one stream, when another stream |
| 79 | becomes active. For example, if music is playing and a notification arrives, |
| 80 | then the music stream could be ducked while the notification plays. |
| 81 | Compare to "mute". |
| 82 | </dd> |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 83 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 84 | <dt>frame</dt> |
| 85 | <dd> |
| 86 | A set of samples, one per channel, at a point in time. |
| 87 | </dd> |
| 88 | |
| 89 | <dt>frames per buffer</dt> |
| 90 | <dd> |
| 91 | The number of frames handed from one module to the next at once; |
| 92 | for example the audio HAL interface uses this concept. |
| 93 | </dd> |
| 94 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 95 | <dt>gain</dt> |
| 96 | <dd> |
| 97 | A multiplicative factor greater than or equal to 1.0, |
| 98 | applied to an audio signal to increase the signal level. |
| 99 | Compare to "attenuation". |
| 100 | </dd> |
| 101 | |
Glenn Kasten | 298f382 | 2013-06-12 17:17:36 -0700 | [diff] [blame] | 102 | <dt>Hz</dt> |
| 103 | <dd> |
| 104 | The units for sample rate or frame rate. |
| 105 | </dd> |
| 106 | |
| 107 | <dt>latency</dt> |
| 108 | <dd> |
| 109 | Time delay as a signal passes through a system. |
| 110 | </dd> |
| 111 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 112 | <dt>mono</dt> |
| 113 | <dd> |
| 114 | One channel. |
| 115 | </dd> |
| 116 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 117 | <dt>multichannel</dt> |
| 118 | <dd> |
| 119 | See "surround sound". |
| 120 | Strictly, since stereo is more than one channel, it is also "multi" channel. |
| 121 | But that usage would be confusing. |
| 122 | </dd> |
| 123 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 124 | <dt>mute</dt> |
| 125 | <dd> |
| 126 | To (temporarily) force volume to be zero, independently from the usual volume controls. |
| 127 | </dd> |
| 128 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 129 | <dt>PCM</dt> |
| 130 | <dd> |
| 131 | Pulse Code Modulation, the most common low-level encoding of digital audio. |
| 132 | The audio signal is sampled at a regular interval, called the sample rate, |
| 133 | and then quantized to discrete values within a particular range depending on the bit depth. |
| 134 | For example, for 16-bit PCM, the sample values are integers between -32768 and +32767. |
| 135 | </dd> |
| 136 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 137 | <dt>ramp</dt> |
| 138 | <dd> |
| 139 | To gradually increase or decrease the level of a particular audio parameter, |
| 140 | for example volume or the strength of an effect. |
| 141 | A volume ramp is commonly applied when pausing and resuming music, to avoid a hard audible transition. |
| 142 | </dd> |
| 143 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 144 | <dt>sample</dt> |
| 145 | <dd> |
| 146 | A number representing the audio value for a single channel at a point in time. |
| 147 | </dd> |
| 148 | |
| 149 | <dt>sample rate or frame rate</dt> |
| 150 | <dd> |
| 151 | Number of frames per second; |
| 152 | note that "frame rate" is thus more accurate, |
Clay Murphy | c28f237 | 2013-09-25 16:13:40 -0700 | [diff] [blame] | 153 | but "sample rate" is conventionally used to mean "frame rate." |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 154 | </dd> |
| 155 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 156 | <dt>sonification</dt> |
| 157 | <dd> |
| 158 | The use of sound to express feedback or information, |
| 159 | for example touch sounds and keyboard sounds. |
| 160 | </dd> |
| 161 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 162 | <dt>stereo</dt> |
| 163 | <dd> |
| 164 | Two channels. |
| 165 | </dd> |
| 166 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 167 | <dt>stereo widening</dt> |
| 168 | <dd> |
| 169 | An effect applied to a stereo signal, to make another stereo signal which sounds fuller and richer. |
| 170 | The effect can also be applied to a mono signal, in which case it is a type of upmixing. |
| 171 | </dd> |
| 172 | |
| 173 | <dt>surround sound</dt> |
| 174 | <dd> |
| 175 | Various techniques for increasing the ability of a listener to perceive |
| 176 | sound position beyond stereo left and right. |
| 177 | </dd> |
| 178 | |
| 179 | <dt>upmixing</dt> |
| 180 | <dd> |
| 181 | To increase the number of channels, e.g. from mono to stereo, or from stereo to surround sound. |
| 182 | This can be accomplished by duplication, panning, or more advanced signal processing. |
| 183 | Compare to "downmixing". |
Glenn Kasten | 795a9de | 2014-01-24 08:58:56 -0800 | [diff] [blame] | 184 | </dd> |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 185 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 186 | <dt>virtualizer</dt> |
| 187 | <dd> |
| 188 | An effect that attempts to spatialize audio channels, such as trying to |
| 189 | simulate more speakers, or give the illusion that various sound sources have position. |
| 190 | </dd> |
| 191 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 192 | <dt>volume</dt> |
| 193 | <dd> |
| 194 | Loudness, the subjective strength of an audio signal. |
| 195 | </dd> |
| 196 | |
Glenn Kasten | 795a9de | 2014-01-24 08:58:56 -0800 | [diff] [blame] | 197 | </dl> |
| 198 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 199 | <h3 id="hardwareTerms">Hardware and Accessories</h3> |
| 200 | |
| 201 | <p> |
| 202 | These terms are related to audio hardware and accessories. |
| 203 | </p> |
| 204 | |
| 205 | <h4 id="interDeviceTerms">Inter-device interconnect</h4> |
| 206 | |
| 207 | <p> |
| 208 | These technologies connect audio and video components between devices, |
| 209 | and are readily visible at the external connectors. The HAL implementor |
| 210 | may need to be aware of these, as well as the end user. |
| 211 | </p> |
| 212 | |
| 213 | <dl> |
| 214 | |
| 215 | <dt>Bluetooth</dt> |
| 216 | <dd> |
| 217 | A short range wireless technology. |
| 218 | The major audio-related |
| 219 | <a class="external-link" href="http://en.wikipedia.org/wiki/Bluetooth_profile" |
| 220 | target="_android">Bluetooth profiles</a> |
| 221 | and |
| 222 | <a class="external-link" href="http://en.wikipedia.org/wiki/Bluetooth_protocols" |
| 223 | target="_android">Bluetooth protocols</a> |
| 224 | are described at these Wikipedia articles: |
| 225 | |
| 226 | <ul> |
| 227 | |
| 228 | <li><a class="external-link" |
| 229 | href="http://en.wikipedia.org/wiki/Bluetooth_profile#Advanced_Audio_Distribution_Profile_.28A2DP.29" |
| 230 | target="_android">A2DP</a> |
| 231 | for music |
| 232 | </li> |
| 233 | |
| 234 | <li><a class="external-link" |
| 235 | href="http://en.wikipedia.org/wiki/Bluetooth_protocols#Synchronous_connection-oriented_.28SCO.29_link" |
| 236 | target="_android">SCO</a> |
| 237 | for telephony |
| 238 | </li> |
| 239 | |
| 240 | </ul> |
| 241 | |
| 242 | </dd> |
| 243 | |
| 244 | <dt>DisplayPort</dt> |
| 245 | <dd> |
| 246 | Digital display interface by VESA. |
| 247 | </dd> |
| 248 | |
| 249 | <dt>HDMI</dt> |
| 250 | <dd> |
| 251 | High-Definition Multimedia Interface, an interface for transferring |
| 252 | audio and video data. For mobile devices, either a micro-HDMI (type D) or MHL connector is used. |
| 253 | </dd> |
| 254 | |
| 255 | <dt>MHL</dt> |
| 256 | <dd> |
| 257 | Mobile High-Definition Link is a mobile audio/video interface, often |
| 258 | over micro-USB connector. |
| 259 | </dd> |
| 260 | |
| 261 | <dt>phone connector</dt> |
| 262 | <dd> |
| 263 | A mini or sub-mini phone connector |
| 264 | connects a device to wired headphones, headset, or line-level amplifier. |
| 265 | </dd> |
| 266 | |
| 267 | <dt>SlimPort</dt> |
| 268 | <dd> |
| 269 | An adapter from micro-USB to HDMI. |
| 270 | </dd> |
| 271 | |
| 272 | <dt>S/PDIF</dt> |
| 273 | <dd> |
| 274 | Sony/Philips Digital Interface Format is an interconnect for uncompressed PCM. |
| 275 | See Wikipedia article <a class="external-link" href="http://en.wikipedia.org/wiki/S/PDIF" |
| 276 | target="_android">S/PDIF</a>. |
| 277 | </dd> |
| 278 | |
| 279 | <dt>USB</dt> |
| 280 | <dd> |
| 281 | Universal Serial Bus. |
| 282 | See Wikipedia article <a class="external-link" href="http://en.wikipedia.org/wiki/USB" target="_android">USB</a>. |
| 283 | </dd> |
| 284 | |
| 285 | </dl> |
| 286 | |
| 287 | <h4 id="intraDeviceTerms">Intra-device interconnect</h4> |
| 288 | |
| 289 | <p> |
| 290 | These technologies connect internal audio components within a given |
| 291 | device, and are not visible without disassembling the device. The HAL |
| 292 | implementor may need to be aware of these, but not the end user. |
| 293 | </p> |
| 294 | |
| 295 | See these Wikipedia articles: |
| 296 | <ul> |
| 297 | <li><a class="external-link" href="http://en.wikipedia.org/wiki/General-purpose_input/output" |
| 298 | target="_android">GPIO</a></li> |
| 299 | <li><a class="external-link" href="http://en.wikipedia.org/wiki/I%C2%B2C" target="_android">I²C</a></li> |
| 300 | <li><a class="external-link" href="http://en.wikipedia.org/wiki/I%C2%B2S" target="_android">I²S</a></li> |
| 301 | <li><a class="external-link" href="http://en.wikipedia.org/wiki/McASP" target="_android">McASP</a></li> |
| 302 | <li><a class="external-link" href="http://en.wikipedia.org/wiki/SLIMbus" target="_android">SLIMbus</a></li> |
| 303 | <li><a class="external-link" href="http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus" |
| 304 | target="_android">SPI</a></li> |
| 305 | </ul> |
| 306 | |
| 307 | <h3 id="signalTerms">Audio Signal Path</h3> |
| 308 | |
| 309 | <p> |
| 310 | These terms are related to the signal path that audio data follows from |
| 311 | an application to the transducer, or vice-versa. |
| 312 | </p> |
| 313 | |
Glenn Kasten | 795a9de | 2014-01-24 08:58:56 -0800 | [diff] [blame] | 314 | <dl> |
| 315 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 316 | <dt>ADC</dt> |
| 317 | <dd> |
| 318 | Analog to digital converter, a module that converts an analog signal |
| 319 | (continuous in both time and amplitude) to a digital signal (discrete in |
| 320 | both time and amplitude). Conceptually, an ADC consists of a periodic |
| 321 | sample-and-hold followed by a quantizer, although it does not have to |
| 322 | be implemented that way. An ADC is usually preceded by a low-pass filter |
| 323 | to remove any high frequency components that are not representable using |
| 324 | the desired sample rate. See Wikipedia article |
| 325 | <a class="external-link" href="http://en.wikipedia.org/wiki/Analog-to-digital_converter" |
| 326 | target="_android">Analog-to-digital_converter</a>. |
| 327 | </dd> |
| 328 | |
| 329 | <dt>AP</dt> |
| 330 | <dd> |
| 331 | Application processor, the main general-purpose computer on a mobile device. |
| 332 | </dd> |
| 333 | |
| 334 | <dt>codec</dt> |
| 335 | <dd> |
| 336 | Coder-decoder, a module that encodes and/or decodes an audio signal |
| 337 | from one representation to another. Typically this is analog to PCM, or PCM to analog. |
| 338 | Strictly, the term "codec" is reserved for modules that both encode and decode, |
| 339 | however it can also more loosely refer to only one of these. |
| 340 | See Wikipedia article |
| 341 | <a class="external-link" href="http://en.wikipedia.org/wiki/Audio_codec" target="_android">Audio codec</a>. |
| 342 | </dd> |
| 343 | |
| 344 | <dt>DAC</dt> |
| 345 | <dd> |
| 346 | Digital to analog converter, a module that converts a digital signal |
| 347 | (discrete in both time and amplitude) to an analog signal |
| 348 | (continuous in both time and amplitude). A DAC is usually followed by |
| 349 | a low-pass filter to remove any high frequency components introduced |
| 350 | by digital quantization. |
| 351 | See Wikipedia article |
| 352 | <a class="external-link" href="http://en.wikipedia.org/wiki/Digital-to-analog_converter" |
| 353 | target="_android">Digital-to-analog converter</a>. |
| 354 | </dd> |
| 355 | |
| 356 | <dt>DSP</dt> |
| 357 | <dd> |
| 358 | Digital Signal Processor, an optional component which is typically located |
| 359 | after the application processor (for output), or before the application processor (for input). |
| 360 | The primary purpose of a DSP is to off-load the application processor, |
| 361 | and provide signal processing features at a lower power cost. |
| 362 | </dd> |
| 363 | |
| 364 | <dt>PDM</dt> |
| 365 | <dd> |
| 366 | Pulse-density modulation |
| 367 | is a form of modulation used to represent an analog signal by a digital signal, |
| 368 | where the relative density of 1s versus 0s indicates the signal level. |
| 369 | It is commonly used by digital to analog converters. |
| 370 | See Wikipedia article |
| 371 | <a class="external-link" href="http://en.wikipedia.org/wiki/Pulse-density_modulation" |
| 372 | target="_android">Pulse-density modulation</a>. |
| 373 | </dd> |
| 374 | |
| 375 | <dt>PWM</dt> |
| 376 | <dd> |
| 377 | Pulse-width modulation |
| 378 | is a form of modulation used to represent an analog signal by a digital signal, |
| 379 | where the relative width of a digital pulse indicates the signal level. |
| 380 | It is commonly used by analog to digital converters. |
| 381 | See Wikipedia article |
| 382 | <a class="external-link" href="http://en.wikipedia.org/wiki/Pulse-width_modulation" |
| 383 | target="_android">Pulse-width modulation</a>. |
| 384 | </dd> |
| 385 | |
Glenn Kasten | 795a9de | 2014-01-24 08:58:56 -0800 | [diff] [blame] | 386 | </dl> |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 387 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 388 | <h2 id="androidSpecificTerms">Android-Specific Terms</h2> |
| 389 | |
| 390 | <p> |
Clay Murphy | c28f237 | 2013-09-25 16:13:40 -0700 | [diff] [blame] | 391 | These are terms specific to the Android audio framework, or that |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 392 | may have a special meaning within Android beyond their general meaning. |
| 393 | </p> |
| 394 | |
| 395 | <dl> |
| 396 | |
| 397 | <dt>ALSA</dt> |
| 398 | <dd> |
| 399 | Advanced Linux Sound Architecture. As the name suggests, it is an audio |
| 400 | framework primarily for Linux, but it has influenced other systems. |
| 401 | See Wikipedia article |
| 402 | <a class="external-link" href="http://en.wikipedia.org/wiki/Advanced_Linux_Sound_Architecture" target="_android">ALSA</a> |
| 403 | for the general definition. As used within Android, it refers primarily |
| 404 | to the kernel audio framework and drivers, not to the user-mode API. See |
| 405 | tinyalsa. |
| 406 | </dd> |
| 407 | |
Glenn Kasten | 298f382 | 2013-06-12 17:17:36 -0700 | [diff] [blame] | 408 | <dt>AudioEffect</dt> |
| 409 | <dd> |
| 410 | An API and implementation framework for output (post-processing) effects |
| 411 | and input (pre-processing) effects. The API is defined at |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 412 | <a href="http://developer.android.com/reference/android/media/audiofx/AudioEffect.html" target="_android">android.media.audiofx.AudioEffect</a>. |
Glenn Kasten | 298f382 | 2013-06-12 17:17:36 -0700 | [diff] [blame] | 413 | </dd> |
| 414 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 415 | <dt>AudioFlinger</dt> |
| 416 | <dd> |
| 417 | The sound server implementation for Android. AudioFlinger |
| 418 | runs within the mediaserver process. See Wikipedia article |
| 419 | <a class="external-link" href="http://en.wikipedia.org/wiki/Sound_server" target="_android">Sound server</a> |
| 420 | for the generic definition. |
| 421 | </dd> |
| 422 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 423 | <dt>audio focus</dt> |
| 424 | <dd> |
| 425 | A set of APIs for managing audio interactions across multiple independent apps. |
| 426 | See <a href="http://developer.android.com/training/managing-audio/audio-focus.html">Managing Audio |
| 427 | Focus</a> and the focus-related methods and constants of |
| 428 | <a href="http://developer.android.com/reference/android/media/AudioManager.html">android.media.AudioManager</a>. |
| 429 | </dd> |
| 430 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 431 | <dt>AudioMixer</dt> |
| 432 | <dd> |
| 433 | The module within AudioFlinger responsible for |
| 434 | combining multiple tracks and applying attenuation |
| 435 | (volume) and certain effects. The Wikipedia article |
| 436 | <a class="external-link" href="http://en.wikipedia.org/wiki/Audio_mixing_(recorded_music)" target="_android">Audio mixing (recorded music)</a> |
| 437 | may be useful for understanding the generic |
| 438 | concept. But that article describes a mixer more as a hardware device |
| 439 | or a software application, rather than a software module within a system. |
| 440 | </dd> |
| 441 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 442 | <dt>audio policy</dt> |
| 443 | <dd> |
| 444 | Service responsible for all actions that require a policy decision |
| 445 | to be made first, such as opening a new I/O stream, re-routing after a |
| 446 | change and stream volume management. |
| 447 | </dd> |
| 448 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 449 | <dt>AudioRecord</dt> |
| 450 | <dd> |
| 451 | The primary low-level client API for receiving data from an audio |
Clay Murphy | c28f237 | 2013-09-25 16:13:40 -0700 | [diff] [blame] | 452 | input device such as microphone. The data is usually in pulse-code modulation |
| 453 | (PCM) format. |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 454 | The API is defined at |
| 455 | <a href="http://developer.android.com/reference/android/media/AudioRecord.html" |
| 456 | target="_android">android.media.AudioRecord</a>. |
| 457 | </dd> |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 458 | |
| 459 | <dt>AudioResampler</dt> |
| 460 | <dd> |
Glenn Kasten | 46ac61c | 2014-01-24 08:59:11 -0800 | [diff] [blame] | 461 | The module within AudioFlinger responsible for |
| 462 | <a href="audio_src.html">sample rate conversion</a>. |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 463 | </dd> |
| 464 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 465 | <dt>AudioTrack</dt> |
| 466 | <dd> |
| 467 | The primary low-level client API for sending data to an audio output |
| 468 | device such as a speaker. The data is usually in PCM format. |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 469 | The API is defined at |
| 470 | <a href="http://developer.android.com/reference/android/media/AudioTrack.html" |
| 471 | target="_android">android.media.AudioTrack</a>. |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 472 | </dd> |
| 473 | |
| 474 | <dt>client</dt> |
| 475 | <dd> |
| 476 | Usually same as application or app, but sometimes the "client" of |
| 477 | AudioFlinger is actually a thread running within the mediaserver system |
| 478 | process. An example of that is when playing media that is decoded by a |
| 479 | MediaPlayer object. |
| 480 | </dd> |
| 481 | |
| 482 | <dt>HAL</dt> |
| 483 | <dd> |
| 484 | Hardware Abstraction Layer. HAL is a generic term in Android. With |
| 485 | respect to audio, it is a layer between AudioFlinger and the kernel |
| 486 | device driver with a C API, which replaces the earlier C++ libaudio. |
| 487 | </dd> |
| 488 | |
| 489 | <dt>FastMixer</dt> |
| 490 | <dd> |
| 491 | A thread within AudioFlinger that services lower latency "fast tracks" |
| 492 | and drives the primary output device. |
| 493 | </dd> |
| 494 | |
| 495 | <dt>fast track</dt> |
| 496 | <dd> |
| 497 | An AudioTrack client with lower latency but fewer features, on some devices. |
| 498 | </dd> |
| 499 | |
| 500 | <dt>MediaPlayer</dt> |
| 501 | <dd> |
| 502 | A higher-level client API than AudioTrack, for playing either encoded |
Clay Murphy | c28f237 | 2013-09-25 16:13:40 -0700 | [diff] [blame] | 503 | content, or content which includes multimedia audio and video tracks. |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 504 | </dd> |
| 505 | |
Glenn Kasten | 298f382 | 2013-06-12 17:17:36 -0700 | [diff] [blame] | 506 | <dt>media.log</dt> |
| 507 | <dd> |
| 508 | An AudioFlinger debugging feature, available in custom builds only, |
| 509 | for logging audio events to a circular buffer where they can then be |
| 510 | dumped retroactively when needed. |
| 511 | </dd> |
| 512 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 513 | <dt>mediaserver</dt> |
| 514 | <dd> |
| 515 | An Android system process that contains a number of media-related |
| 516 | services, including AudioFlinger. |
| 517 | </dd> |
| 518 | |
| 519 | <dt>NBAIO</dt> |
| 520 | <dd> |
| 521 | An abstraction for "non-blocking" audio input/output ports used within |
| 522 | AudioFlinger. The name can be misleading, as some implementations of |
| 523 | the NBAIO API actually do support blocking. The key implementations of |
| 524 | NBAIO are for pipes of various kinds. |
| 525 | </dd> |
| 526 | |
| 527 | <dt>normal mixer</dt> |
| 528 | <dd> |
| 529 | A thread within AudioFlinger that services most full-featured |
| 530 | AudioTrack clients, and either directly drives an output device or feeds |
Clay Murphy | c28f237 | 2013-09-25 16:13:40 -0700 | [diff] [blame] | 531 | its sub-mix into FastMixer via a pipe. |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 532 | </dd> |
| 533 | |
| 534 | <dt>OpenSL ES</dt> |
| 535 | <dd> |
| 536 | An audio API standard by The Khronos Group. Android versions since |
| 537 | API level 9 support a native audio API which is based on a subset of |
| 538 | OpenSL ES 1.0.1. |
| 539 | </dd> |
| 540 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 541 | <dt>silent mode</dt> |
| 542 | <dd> |
| 543 | A user-settable feature to mute the phone ringer and notifications, |
| 544 | without affecting media playback (music, videos, games) or alarms. |
| 545 | </dd> |
| 546 | |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 547 | <dt>SoundPool</dt> |
| 548 | <dd> |
| 549 | A higher-level client API than AudioTrack, used for playing sampled |
| 550 | audio clips. It is useful for triggering UI feedback, game sounds, etc. |
| 551 | The API is defined at |
| 552 | <a href="http://developer.android.com/reference/android/media/SoundPool.html" |
| 553 | target="_android">android.media.SoundPool</a>. |
| 554 | </dd> |
Glenn Kasten | 5df2d52 | 2013-09-27 11:50:35 -0700 | [diff] [blame] | 555 | |
| 556 | <dt>Stagefright</dt> |
| 557 | <dd> |
| 558 | See <a href="{@docRoot}devices/media.html">Media</a>. |
| 559 | </dd> |
| 560 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 561 | <dt>StateQueue</dt> |
| 562 | <dd> |
| 563 | A module within AudioFlinger responsible for synchronizing state |
| 564 | among threads. Whereas NBAIO is used to pass data, StateQueue is used |
| 565 | to pass control information. |
| 566 | </dd> |
| 567 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 568 | <dt>strategy</dt> |
| 569 | <dd> |
| 570 | A grouping of stream types with similar behavior, used by the audio policy service. |
| 571 | </dd> |
| 572 | |
| 573 | <dt>stream type</dt> |
| 574 | <dd> |
| 575 | An enumeration that expresses a use case for audio output. |
| 576 | The audio policy implementation uses the stream type, along with other parameters, |
| 577 | to determine volume and routing decisions. |
| 578 | Specific stream types are listed at |
| 579 | <a href="http://developer.android.com/reference/android/media/AudioManager.html">android.media.AudioManager</a>. |
| 580 | </dd> |
| 581 | |
Glenn Kasten | 298f382 | 2013-06-12 17:17:36 -0700 | [diff] [blame] | 582 | <dt>tee sink</dt> |
| 583 | <dd> |
Glenn Kasten | 37784a5 | 2014-02-03 11:57:33 -0800 | [diff] [blame] | 584 | See the separate article on tee sink in |
| 585 | <a href="audio_debugging.html#teeSink">Audio Debugging</a>. |
Glenn Kasten | 298f382 | 2013-06-12 17:17:36 -0700 | [diff] [blame] | 586 | </dd> |
| 587 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 588 | <dt>tinyalsa</dt> |
| 589 | <dd> |
| 590 | A small user-mode API above ALSA kernel with BSD license, recommended |
Clay Murphy | c28f237 | 2013-09-25 16:13:40 -0700 | [diff] [blame] | 591 | for use in HAL implementations. |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 592 | </dd> |
| 593 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 594 | <dt>ToneGenerator</dt> |
| 595 | <dd> |
| 596 | A higher-level client API than AudioTrack, used for playing DTMF signals. |
| 597 | See the Wikipedia article |
| 598 | <a class="external-link" href="http://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling" |
| 599 | target="_android">Dual-tone multi-frequency signaling</a>, |
| 600 | and the API definition at |
| 601 | <a href="http://developer.android.com/reference/android/media/ToneGenerator.html" |
| 602 | target="_android">android.media.ToneGenerator</a>. |
| 603 | </dd> |
| 604 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 605 | <dt>track</dt> |
| 606 | <dd> |
| 607 | An audio stream, controlled by the AudioTrack API. |
| 608 | </dd> |
| 609 | |
Glenn Kasten | fdc7b7b | 2013-10-28 11:11:34 -0700 | [diff] [blame] | 610 | <dt>volume attenuation curve</dt> |
| 611 | <dd> |
| 612 | A device-specific mapping from a generic volume index to a particular attenuation factor |
| 613 | for a given output. |
| 614 | </dd> |
| 615 | |
| 616 | <dt>volume index</dt> |
| 617 | <dd> |
| 618 | A unitless integer that expresses the desired relative volume of a stream. |
| 619 | The volume-related APIs of |
| 620 | <a href="http://developer.android.com/reference/android/media/AudioManager.html">android.media.AudioManager</a> |
| 621 | operate in volume indices rather than absolute attenuation factors. |
| 622 | </dd> |
| 623 | |
Glenn Kasten | 963fd95 | 2013-04-18 17:26:23 -0700 | [diff] [blame] | 624 | </dl> |
| 625 | |
Glenn Kasten | 46ac61c | 2014-01-24 08:59:11 -0800 | [diff] [blame] | 626 | <h2 id="srcTerms">Sample Rate Conversion</h2> |
| 627 | |
| 628 | <p> |
| 629 | For terms related to sample rate conversion, see the separate article |
| 630 | <a href="audio_src.html">Sample Rate Conversion</a>. |
| 631 | </p> |
| 632 | |