[linux-audio-user] Copying one channel from a Stereo File with sox

[wes schreiner]

Martin McCormick wrote:

>	I am confused.  The man page for sox lists what appears to be
>an effect called pick in which you provide it with a channel number
>from 1 to 4 or a -l or -r flag to select either left or right audio to
>feed to the output file.
>
>	After getting complaints from sox, I listed the -help output
>and got:
>
>sox: Known effects: avg band bandpass bandreject chorus compand copy 
>dcshift deemph earwax echo echos fade filter flanger highp highpass 
>lowp lowpass map mask pan phaser pitch polyphase rate resample 
>reverb reverse silence speed stat stretch swap synth trim vibro vol 
>
>no pick.  The manual contains the following passage:
>
>	   phaser gain-in gain-out delay decay speed < -s | -t >
>	   pick [ -1 | -2 | -3 | -4 | -l | -r ]
>	   pitch shift [ width interpole fade ]
>	   polyphase [ -w < nut / ham > ]
>
>	Is this something peculiar to the Debian distribution for sox
>or what?  Am I just misunderstanding the instructions and trying to
>use  pick  in the wrong way?
>
>	Thank you.
>
>Martin McCormick WB5AGZ  Stillwater, OK 
>OSU Information Technology Division Network Operations Group
>  
>
It is just a slightly outdated man page.  You must be looking at Debian 
stable, because Debian testing has the man page in sync with the 
executable.  What you want is the "avg" effect.   So to take only the 
left channel of a stereo WAV file, one could give the command:

sox stereo.wav -c 1 mono.wav avg -l

For the other channel:

sox stereo.wav -c 1 mono.wav avg -r

wes