Add more audio terminology
Also put "audio policy" in alphabetical order.
Change-Id: I822977f608818506736f4a28eed5fb2309c43c95
diff --git a/src/devices/audio_terminology.jd b/src/devices/audio_terminology.jd
index 23592d4..f61c74c 100644
--- a/src/devices/audio_terminology.jd
+++ b/src/devices/audio_terminology.jd
@@ -21,6 +21,8 @@
These are audio terms that are widely used, with their conventional meanings.
</p>
+<h3 id="digitalAudioTerms">Digital Audio</h3>
+
<dl>
<dt>acoustics</dt>
@@ -30,6 +32,13 @@
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".
+</dd>
+
<dt>bits per sample or bit depth</dt>
<dd>
Number of bits of information per sample.
@@ -41,6 +50,14 @@
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".
+</dl>
+
<dt>frame</dt>
<dd>
A set of samples, one per channel, at a point in time.
@@ -52,6 +69,13 @@
for example the audio HAL interface uses this concept.
</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".
+</dd>
+
<dt>Hz</dt>
<dd>
The units for sample rate or frame rate.
@@ -67,6 +91,21 @@
One channel.
</dd>
+<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.
+</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.
+</dd>
+
<dt>sample</dt>
<dd>
A number representing the audio value for a single channel at a point in time.
@@ -84,8 +123,218 @@
Two channels.
</dd>
+<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.
+</dd>
+
+<dt>surround sound</dt>
+<dd>
+Various techniques for increasing the ability of a listener to perceive
+sound position beyond stereo left and right.
+</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".
</dl>
+<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.
+</dd>
+
+<h3 id="hardwareTerms">Hardware and Accessories</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.
+</p>
+
+<dl>
+
+<dt>Bluetooth</dt>
+<dd>
+A short range wireless technology.
+The major audio-related
+<a class="external-link" href="http://en.wikipedia.org/wiki/Bluetooth_profile"
+target="_android">Bluetooth profiles</a>
+and
+<a class="external-link" href="http://en.wikipedia.org/wiki/Bluetooth_protocols"
+target="_android">Bluetooth protocols</a>
+are described at these Wikipedia articles:
+
+<ul>
+
+<li><a class="external-link"
+href="http://en.wikipedia.org/wiki/Bluetooth_profile#Advanced_Audio_Distribution_Profile_.28A2DP.29"
+target="_android">A2DP</a>
+for music
+</li>
+
+<li><a class="external-link"
+href="http://en.wikipedia.org/wiki/Bluetooth_protocols#Synchronous_connection-oriented_.28SCO.29_link"
+target="_android">SCO</a>
+for telephony
+</li>
+
+</ul>
+
+</dd>
+
+<dt>DisplayPort</dt>
+<dd>
+Digital display interface by 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.
+</dd>
+
+<dt>MHL</dt>
+<dd>
+Mobile High-Definition Link is a 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.
+</dd>
+
+<dt>SlimPort</dt>
+<dd>
+An 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 class="external-link" href="http://en.wikipedia.org/wiki/S/PDIF"
+target="_android">S/PDIF</a>.
+</dd>
+
+<dt>USB</dt>
+<dd>
+Universal Serial Bus.
+See Wikipedia article <a class="external-link" href="http://en.wikipedia.org/wiki/USB" target="_android">USB</a>.
+</dd>
+
+</dl>
+
+<h4 id="intraDeviceTerms">Intra-device interconnect</h4>
+
+<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>
+
+See these Wikipedia articles:
+<ul>
+<li><a class="external-link" href="http://en.wikipedia.org/wiki/General-purpose_input/output"
+target="_android">GPIO</a></li>
+<li><a class="external-link" href="http://en.wikipedia.org/wiki/I%C2%B2C" target="_android">I²C</a></li>
+<li><a class="external-link" href="http://en.wikipedia.org/wiki/I%C2%B2S" target="_android">I²S</a></li>
+<li><a class="external-link" href="http://en.wikipedia.org/wiki/McASP" target="_android">McASP</a></li>
+<li><a class="external-link" href="http://en.wikipedia.org/wiki/SLIMbus" target="_android">SLIMbus</a></li>
+<li><a class="external-link" href="http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus"
+target="_android">SPI</a></li>
+</ul>
+
+<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.
+</p>
+
+<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 class="external-link" href="http://en.wikipedia.org/wiki/Analog-to-digital_converter"
+target="_android">Analog-to-digital_converter</a>.
+</dd>
+
+<dt>AP</dt>
+<dd>
+Application processor, the 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
+<a class="external-link" href="http://en.wikipedia.org/wiki/Audio_codec" target="_android">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 class="external-link" href="http://en.wikipedia.org/wiki/Digital-to-analog_converter"
+target="_android">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.
+</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 class="external-link" href="http://en.wikipedia.org/wiki/Pulse-density_modulation"
+target="_android">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 class="external-link" href="http://en.wikipedia.org/wiki/Pulse-width_modulation"
+target="_android">Pulse-width modulation</a>.
+</dd>
+
+</p>
+
<h2 id="androidSpecificTerms">Android-Specific Terms</h2>
<p>
@@ -110,7 +359,7 @@
<dd>
An API and implementation framework for output (post-processing) effects
and input (pre-processing) effects. The API is defined at
-<a class="external-link" href="http://developer.android.com/reference/android/media/audiofx/AudioEffect.html" target="_android">android.media.audiofx.AudioEffect</a>
+<a href="http://developer.android.com/reference/android/media/audiofx/AudioEffect.html" target="_android">android.media.audiofx.AudioEffect</a>.
</dd>
<dt>AudioFlinger</dt>
@@ -132,11 +381,22 @@
or a 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.
+</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
+<a href="http://developer.android.com/reference/android/media/AudioRecord.html"
+target="_android">android.media.AudioRecord</a>.
+</dd>
</dd>
<dt>AudioResampler</dt>
@@ -146,17 +406,13 @@
for the generic definition.
</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.
-</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
+<a href="http://developer.android.com/reference/android/media/AudioTrack.html"
+target="_android">android.media.AudioTrack</a>.
</dd>
<dt>client</dt>
@@ -226,6 +482,21 @@
OpenSL ES 1.0.1.
</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
+<a href="http://developer.android.com/reference/android/media/SoundPool.html"
+target="_android">android.media.SoundPool</a>.
+</dd>
+</dd>
+
+<dt>Stagefright</dt>
+<dd>
+See <a href="{@docRoot}devices/media.html">Media</a>.
+</dd>
+
<dt>StateQueue</dt>
<dd>
A module within AudioFlinger responsible for synchronizing state