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--- old/usr/src/man/man7d/audio.7d.man.txt
+++ new/usr/src/man/man7d/audio.7d.man.txt
1 1 AUDIO(7D) Devices AUDIO(7D)
2 2
3 3
4 4
5 5 NAME
6 6 audio - common audio framework
7 7
8 8 DESCRIPTION
9 9 The audio driver provides common support routines for audio devices in
10 10 Solaris.
11 11
12 12
13 13 The audio framework supports multiple personalities, allowing for
14 14 devices to be accessed with different programming interfaces.
15 15
16 16
17 17 The audio framework also provides a number of facilities, such as
18 18 mixing of audio streams, and data format and sample rate conversion.
19 19
20 20 Overview
21 21 The audio framework provides a software mixing engine (audio mixer) for
22 22 all audio devices, allowing more than one process to play or record
23 23 audio at the same time.
24 24
25 25 Multi-Stream Codecs
26 26 The audio mixer supports multi-stream Codecs. These devices have DSP
27 27 engines that provide sample rate conversion, hardware mixing, and
28 28 other features. The use of such hardware features is opaque to
29 29 applications.
30 30
31 31 Backward Compatibility
32 32 It is not possible to disable the mixing function. Applications must
33 33 not assume that they have exclusive access to the audio device.
34 34
35 35 Audio Formats
36 36 Digital audio data represents a quantized approximation of an analog
37 37 audio signal waveform. In the simplest case, these quantized numbers
38 38 represent the amplitude of the input waveform at particular sampling
39 39 intervals. To achieve the best approximation of an input signal, the
40 40 highest possible sampling frequency and precision should be used.
41 41 However, increased accuracy comes at a cost of increased data storage
42 42 requirements. For instance, one minute of monaural audio recorded in u-
43 43 Law format (pronounced mew-law) at 8 KHz requires nearly 0.5 megabytes
44 44 of storage, while the standard Compact Disc audio format (stereo 16-bit
45 45 linear PCM data sampled at 44.1 KHz) requires approximately 10
46 46 megabytes per minute.
47 47
48 48
49 49 An audio data format is characterized in the audio driver by four
50 50 parameters: sample Rate, encoding, precision, and channels. Refer to
51 51 the device-specific manual pages for a list of the audio formats that
52 52 each device supports. In addition to the formats that the audio device
53 53 supports directly, other formats provide higher data compression.
54 54 Applications can convert audio data to and from these formats when
55 55 playing or recording.
56 56
57 57 Sample Rate
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58 58 Sample rate is a number that represents the sampling frequency (in
59 59 samples per second) of the audio data.
60 60
61 61
62 62 The audio mixer always configures the hardware for the highest possible
63 63 sample rate for both play and record. This ensures that none of the
64 64 audio streams require compute-intensive low pass filtering. The result
65 65 is that high sample rate audio streams are not degraded by filtering.
66 66
67 67
68 - Sample rate conversion can be a compute-intensive operation,
69 - dependingon the number of channels and a device's sample rate. For
70 - example, an 8KHz signal can be easily converted to 48KHz, requiring a
71 - low cost up sampling by 6. However, converting from 44.1KHz to 48KHz is
72 - computer intensive because it must be up sampled by 160 and then down
73 - sampled by 147. This is only done using integer multipliers.
68 + Sample rate conversion can be a compute-intensive operation, depending
69 + on the number of channels and a device's sample rate. For example, an
70 + 8KHz signal can be easily converted to 48KHz, requiring a low cost up
71 + sampling by 6. However, converting from 44.1KHz to 48KHz is computer
72 + intensive because it must be up sampled by 160 and then down sampled by
73 + 147. This is only done using integer multipliers.
74 74
75 75
76 76 Applications can greatly reduce the impact of sample rate conversion by
77 77 carefully picking the sample rate. Applications should always use the
78 78 highest sample rate the device supports. An application can also do its
79 79 own sample rate conversion (to take advantage of floating point and
80 80 accelerated instructions) or use small integers for up and down
81 81 sampling.
82 82
83 83
84 84 All modern audio devices run at 48 kHz or a multiple thereof, hence
85 85 just using 48 kHz can be a reasonable compromise if the application is
86 86 not prepared to select higher sample rates.
87 87
88 88 Encodings
89 89 An encoding parameter specifies the audiodata representation. u-Law
90 90 encoding corresponds to CCITT G.711, and is the standard for voice data
91 91 used by telephone companies in the United States, Canada, and Japan. A-
92 92 Law encoding is also part of CCITT G.711 and is the standard encoding
93 93 for telephony elsewhere in the world. A-Law and u-Law audio data are
94 94 sampled at a rate of 8000 samples per second with 12-bit precision,
95 95 with the data compressed to 8-bit samples. The resulting audio data
96 96 quality is equivalent to that of stan dard analog telephone service.
97 97
98 98
99 99 Linear Pulse Code Modulation (PCM) is an uncompressed, signed audio
100 100 format in which sample values are directly proportional to audio signal
101 101 voltages. Each sample is a 2's complement number that represents a
102 102 positive or negative amplitude.
103 103
104 104 Precision
105 105 Precision indicates the number of bits used to store each audio sample.
106 106 For instance, u-Law and A-Law data are stored with 8-bit precision. PCM
107 107 data can be stored at various precisions, though 16-bit is the most
108 108 common.
109 109
110 110 Channels
111 111 Multiple channels of audio can be interleaved at sample boundaries. A
112 112 sample frame consists of a single sample from each active channel. For
113 113 example, a sample frame of stereo 16-bit PCM data consists of 2 16-bit
114 114 samples, corresponding to the left and right channel data. The audio
115 115 mixer sets the hardware to the maximum number of channels supported. If
116 116 a mono signal is played or recorded, it is mixed on the first two
117 117 (usually the left and right) channel only. Silence is mixed on the
118 118 remaining channels.
119 119
120 120 Supported Formats
121 121 The audio mixer supports the following audio formats:
122 122
123 123 Encoding Precision Channels
124 124 Signed Linear PCM 32-bit Mono or Stereo
125 125 Signed Linear PCM 16-bit Mono or Stereo
126 126 Signed Linear PCM 8-bit Mono or Stereo
127 127 u-Law 8-bit Mono or Stereo
128 128 A-Law 8-bit Mono or Stereo
129 129
130 130
131 131
132 132
133 133 The audio mixer converts all audio streams to 24-bit Linear PCM before
134 134 mixing. After mixing, conversion is made to the best possible Codec
135 135 format. The conversion process is not compute intensive and audio
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136 136 applications can choose the encoding format that best meets their
137 137 needs.
138 138
139 139
140 140 The mixer discards the low order 8 bits of 32-bit Signed Linear PCM in
141 141 order to perform mixing. (This is done to allow for possible overflows
142 142 to fit into 32-bits when mixing multiple streams together.) Hence, the
143 143 maximum effective precision is 24-bits.
144 144
145 145 FILES
146 - /kernel/drv/audio
147 - 32-bit kernel driver module
148 -
149 -
150 146 /kernel/drv/amd64/audio
151 - 64-bit x86 kernel driver module
147 + Device driver (x86)
152 148
153 149
154 150 /kernel/drv/sparcv9/audio
155 - 64-bit SPARC kernel driver module
151 + Device driver (SPARC)
156 152
157 153
158 154 /kernel/drv/audio.conf
159 - audio configuration file
155 + Driver configuration file
160 156
161 157
162 158 ATTRIBUTES
163 159 See attributes(5) for a description of the following attributes:
164 160
165 161
166 162
167 163
168 164 +--------------------+-----------------+
169 165 |ATTRIBUTE TYPE | ATTRIBUTE VALUE |
170 166 +--------------------+-----------------+
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171 167 |Architecture | SPARC, x86 |
172 168 +--------------------+-----------------+
173 169 |Interface Stability | Uncommitted |
174 170 +--------------------+-----------------+
175 171
176 172 SEE ALSO
177 173 ioctl(2), attributes(5), audio(7I), dsp(7I)
178 174
179 175
180 176
181 - August 3, 2009 AUDIO(7D)
177 + January 10, 2020 AUDIO(7D)
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