48
49 An audio data format is characterized in the audio driver by four
50 parameters: sample Rate, encoding, precision, and channels. Refer to
51 the device-specific manual pages for a list of the audio formats that
52 each device supports. In addition to the formats that the audio device
53 supports directly, other formats provide higher data compression.
54 Applications can convert audio data to and from these formats when
55 playing or recording.
56
57 Sample Rate
58 Sample rate is a number that represents the sampling frequency (in
59 samples per second) of the audio data.
60
61
62 The audio mixer always configures the hardware for the highest possible
63 sample rate for both play and record. This ensures that none of the
64 audio streams require compute-intensive low pass filtering. The result
65 is that high sample rate audio streams are not degraded by filtering.
66
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.
74
75
76 Applications can greatly reduce the impact of sample rate conversion by
77 carefully picking the sample rate. Applications should always use the
78 highest sample rate the device supports. An application can also do its
79 own sample rate conversion (to take advantage of floating point and
80 accelerated instructions) or use small integers for up and down
81 sampling.
82
83
84 All modern audio devices run at 48 kHz or a multiple thereof, hence
85 just using 48 kHz can be a reasonable compromise if the application is
86 not prepared to select higher sample rates.
87
88 Encodings
89 An encoding parameter specifies the audiodata representation. u-Law
90 encoding corresponds to CCITT G.711, and is the standard for voice data
91 used by telephone companies in the United States, Canada, and Japan. A-
92 Law encoding is also part of CCITT G.711 and is the standard encoding
93 for telephony elsewhere in the world. A-Law and u-Law audio data are
126 Signed Linear PCM 8-bit Mono or Stereo
127 u-Law 8-bit Mono or Stereo
128 A-Law 8-bit Mono or Stereo
129
130
131
132
133 The audio mixer converts all audio streams to 24-bit Linear PCM before
134 mixing. After mixing, conversion is made to the best possible Codec
135 format. The conversion process is not compute intensive and audio
136 applications can choose the encoding format that best meets their
137 needs.
138
139
140 The mixer discards the low order 8 bits of 32-bit Signed Linear PCM in
141 order to perform mixing. (This is done to allow for possible overflows
142 to fit into 32-bits when mixing multiple streams together.) Hence, the
143 maximum effective precision is 24-bits.
144
145 FILES
146 /kernel/drv/audio
147 32-bit kernel driver module
148
149
150 /kernel/drv/amd64/audio
151 64-bit x86 kernel driver module
152
153
154 /kernel/drv/sparcv9/audio
155 64-bit SPARC kernel driver module
156
157
158 /kernel/drv/audio.conf
159 audio configuration file
160
161
162 ATTRIBUTES
163 See attributes(5) for a description of the following attributes:
164
165
166
167
168 +--------------------+-----------------+
169 |ATTRIBUTE TYPE | ATTRIBUTE VALUE |
170 +--------------------+-----------------+
171 |Architecture | SPARC, x86 |
172 +--------------------+-----------------+
173 |Interface Stability | Uncommitted |
174 +--------------------+-----------------+
175
176 SEE ALSO
177 ioctl(2), attributes(5), audio(7I), dsp(7I)
178
179
180
181 August 3, 2009 AUDIO(7D)
|
48
49 An audio data format is characterized in the audio driver by four
50 parameters: sample Rate, encoding, precision, and channels. Refer to
51 the device-specific manual pages for a list of the audio formats that
52 each device supports. In addition to the formats that the audio device
53 supports directly, other formats provide higher data compression.
54 Applications can convert audio data to and from these formats when
55 playing or recording.
56
57 Sample Rate
58 Sample rate is a number that represents the sampling frequency (in
59 samples per second) of the audio data.
60
61
62 The audio mixer always configures the hardware for the highest possible
63 sample rate for both play and record. This ensures that none of the
64 audio streams require compute-intensive low pass filtering. The result
65 is that high sample rate audio streams are not degraded by filtering.
66
67
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
75
76 Applications can greatly reduce the impact of sample rate conversion by
77 carefully picking the sample rate. Applications should always use the
78 highest sample rate the device supports. An application can also do its
79 own sample rate conversion (to take advantage of floating point and
80 accelerated instructions) or use small integers for up and down
81 sampling.
82
83
84 All modern audio devices run at 48 kHz or a multiple thereof, hence
85 just using 48 kHz can be a reasonable compromise if the application is
86 not prepared to select higher sample rates.
87
88 Encodings
89 An encoding parameter specifies the audiodata representation. u-Law
90 encoding corresponds to CCITT G.711, and is the standard for voice data
91 used by telephone companies in the United States, Canada, and Japan. A-
92 Law encoding is also part of CCITT G.711 and is the standard encoding
93 for telephony elsewhere in the world. A-Law and u-Law audio data are
126 Signed Linear PCM 8-bit Mono or Stereo
127 u-Law 8-bit Mono or Stereo
128 A-Law 8-bit Mono or Stereo
129
130
131
132
133 The audio mixer converts all audio streams to 24-bit Linear PCM before
134 mixing. After mixing, conversion is made to the best possible Codec
135 format. The conversion process is not compute intensive and audio
136 applications can choose the encoding format that best meets their
137 needs.
138
139
140 The mixer discards the low order 8 bits of 32-bit Signed Linear PCM in
141 order to perform mixing. (This is done to allow for possible overflows
142 to fit into 32-bits when mixing multiple streams together.) Hence, the
143 maximum effective precision is 24-bits.
144
145 FILES
146 /kernel/drv/amd64/audio
147 Device driver (x86)
148
149
150 /kernel/drv/sparcv9/audio
151 Device driver (SPARC)
152
153
154 /kernel/drv/audio.conf
155 Driver configuration file
156
157
158 ATTRIBUTES
159 See attributes(5) for a description of the following attributes:
160
161
162
163
164 +--------------------+-----------------+
165 |ATTRIBUTE TYPE | ATTRIBUTE VALUE |
166 +--------------------+-----------------+
167 |Architecture | SPARC, x86 |
168 +--------------------+-----------------+
169 |Interface Stability | Uncommitted |
170 +--------------------+-----------------+
171
172 SEE ALSO
173 ioctl(2), attributes(5), audio(7I), dsp(7I)
174
175
176
177 January 10, 2020 AUDIO(7D)
|