aucat -c playback channels confusion

[Jan Stary]

This is current/amd64. I am trying to use the -c option of aucat,
specifying the channels to be played from a multichannel file.

As an example, here is a quad audio file produced by sox:

$ sox -n -b 16 quad.wav synth 10 sin 200 sin 300 sin 400 sin 600 gain -6
$ soxi quad.wav

Input File : 'quad.wav'
Channels : 4
Sample Rate : 48000
Precision : 16-bit
Duration : 00:00:10.00 = 480000 samples ~ 750 CDDA sectors
File Size : 3.84M
Bit Rate : 3.07M
Sample Encoding: 16-bit Signed Integer PCM


Now trying to use aucat -c to play the individual channels
doesn't seem to do what it says:

$ aucat -dd -c 0:0 -i quad.wav
quad.wav: skipped unknown chunk
quad.wav,pst=cfg: play, chan 0:3, 48000Hz, s16le, bytes 80..3840080, vol 32768
default: 48000Hz, play 0:3, 36 blocks of 480 frames
quad.wav,pst=cfg: allocated 17280 frame buffer
cmap: nch = 4, ostart = 0, onext = 0, istart = 0, inext = 0
quad.wav,pst=ini: chain initialized
quad.wav,pst=run: started
started
^Cquad.wav,pst=ini: stopped
stopped
quad.wav,pst=ini: closed


Indeed quad.wav has channels 0:3, but why does auact play channels 0:3
with -c 0:0 specified? Specifying other channels seem even more confusing:

$ aucat -dd -c 2:2 -i quad.wav
quad.wav: skipped unknown chunk
quad.wav,pst=cfg: play, chan 2:5, 48000Hz, s16le, bytes 80..3840080, vol 32768
default: 48000Hz, play 0:5, 36 blocks of 480 frames
quad.wav,pst=cfg: allocated 17280 frame buffer
cmap: nch = 4, ostart = 2, onext = 0, istart = 0, inext = 0
quad.wav,pst=ini: chain initialized
quad.wav,pst=run: started
started
^Cquad.wav,pst=ini: stopped
stopped
quad.wav,pst=ini: closed

Now it considers quad.wav to have channels 2 to 5
and it plays channels 0:5, given -c 2:2.

Maybe I am misunderstanding the -c option
(or what the -dd messages say):

-c min:max The range of audio file channel numbers.
The default is 0:1, i.e. stereo.

When playing a file with aucat -i, does that mean
"use these channels from the file"?

If not, how does one specify "play just channel 2, out of 0,1,2,3"?

There is a chunk that aucat skips; this is what sndfile-info says:

File : quad.wav
Length : 384080
RIFF : 384072
WAVE
fmt : 40
Format : 0xFFFE => WAVE_FORMAT_EXTENSIBLE
Channels : 4
Sample Rate : 48000
Block Align : 8
Bit Width : 16
Bytes/sec : 384000
Valid Bits : 16
Channel Mask : 0x33 (L, R, Ls, Rs)
Subformat
esf_field1 : 0x1
esf_field2 : 0x0
esf_field3 : 0x10
esf_field4 : 0x80 0x0 0x0 0xAA 0x0 0x38 0x9B 0x71
format : pcm
fact : 4
frames : 48000
data : 384000
End

----------------------------------------
Sample Rate : 48000
Frames : 48000
Channels : 4
Format : 0x00130002
Sections : 1
Seekable : TRUE
Duration : 00:00:01.000
Signal Max : 16424 (-6.00 dB)


With 1 second instead of 10 seconds of audio (synth 1) the file
is small enough, I am attaching it.

Thanks for any clue.

Jan

[Alexandre Ratchov]

Post by Jan Stary
This is current/amd64. I am trying to use the -c option of aucat,
specifying the channels to be played from a multichannel file.
$ sox -n -b 16 quad.wav synth 10 sin 200 sin 300 sin 400 sin 600 gain -6
$ soxi quad.wav
Input File : 'quad.wav'
Channels : 4
Sample Rate : 48000
Precision : 16-bit
Duration : 00:00:10.00 = 480000 samples ~ 750 CDDA sectors
File Size : 3.84M
Bit Rate : 3.07M
Sample Encoding: 16-bit Signed Integer PCM
Now trying to use aucat -c to play the individual channels
$ aucat -dd -c 0:0 -i quad.wav
quad.wav: skipped unknown chunk
quad.wav,pst=cfg: play, chan 0:3, 48000Hz, s16le, bytes 80..3840080, vol 32768
default: 48000Hz, play 0:3, 36 blocks of 480 frames
quad.wav,pst=cfg: allocated 17280 frame buffer
cmap: nch = 4, ostart = 0, onext = 0, istart = 0, inext = 0
quad.wav,pst=ini: chain initialized
quad.wav,pst=run: started
started
^Cquad.wav,pst=ini: stopped
stopped
quad.wav,pst=ini: closed
Indeed quad.wav has channels 0:3, but why does auact play channels 0:3
$ aucat -dd -c 2:2 -i quad.wav
quad.wav: skipped unknown chunk
quad.wav,pst=cfg: play, chan 2:5, 48000Hz, s16le, bytes 80..3840080, vol 32768
default: 48000Hz, play 0:5, 36 blocks of 480 frames
quad.wav,pst=cfg: allocated 17280 frame buffer
cmap: nch = 4, ostart = 2, onext = 0, istart = 0, inext = 0
quad.wav,pst=ini: chain initialized
quad.wav,pst=run: started
started
^Cquad.wav,pst=ini: stopped
stopped
quad.wav,pst=ini: closed
Now it considers quad.wav to have channels 2 to 5
and it plays channels 0:5, given -c 2:2.
Maybe I am misunderstanding the -c option
-c min:max The range of audio file channel numbers.
The default is 0:1, i.e. stereo.
When playing a file with aucat -i, does that mean
"use these channels from the file"?
If not, how does one specify "play just channel 2, out of 0,1,2,3"?
File : quad.wav
Length : 384080
RIFF : 384072
WAVE
fmt : 40
Format : 0xFFFE => WAVE_FORMAT_EXTENSIBLE
Channels : 4
Sample Rate : 48000
Block Align : 8
Bit Width : 16
Bytes/sec : 384000
Valid Bits : 16
Channel Mask : 0x33 (L, R, Ls, Rs)
Subformat
esf_field1 : 0x1
esf_field2 : 0x0
esf_field3 : 0x10
esf_field4 : 0x80 0x0 0x0 0xAA 0x0 0x38 0x9B 0x71
format : pcm
fact : 4
frames : 48000
data : 384000
End
----------------------------------------
Sample Rate : 48000
Frames : 48000
Channels : 4
Format : 0x00130002
Sections : 1
Seekable : TRUE
Duration : 00:00:01.000
Signal Max : 16424 (-6.00 dB)
With 1 second instead of 10 seconds of audio (synth 1) the file
is small enough, I am attaching it.
Thanks for any clue.

Hi,

The -c, -e, and -r options are used to specify file's channels,
encoding and rate in case they are undefined, typically for raw data
files. The .wav file header of quad.wav contains the number of
channels (but not the initial channel). So, in your example, the
number of channel is taken from the .wav header, that's why you hear
all channels. The -c option is used only to determine the starting
channel.

For output .wav files -c make sense, though. For instance:

aucat -n -i quad.wav -c 1:1 -o quad-1.wav

extracts channel 1 into a mono file. Here -c 1:1 specifies channels
selection of the output file. Then, playing quad-1.wav will, in turn,
play channel 1 of the quad.wav file.

[Jan Stary]

Post by Jan Stary
With 1 second instead of 10 seconds of audio (synth 1) the file
is small enough, I am attaching it.

(Now I am, sorry.)