At Wed, 12 Dec 2007 16:04:37 -0700, Steve Strobel wrote:

I am using a 4-input, 8-output codec (AD1938) in an application similar to a live sound mixing board, where a combination of the input signals get mixed for each output. I can mix four inputs to four outputs with a command like:

    arecord --file-type raw --channels=4 --format=S32_LE --rate=16000 \
     | crosspoint \
     | aplay  --file-type raw --channels=4 --format=S32_LE --rate=16000

where crosspoint is a simple program that reads from stdin, does some mixing, and outputs to stdout.

My next step is to play and record wave files from the various channels, while the crosspoint is running. For example, I might need to play message1.wav to channel 2 and message2.wav to channel 3 while recording channel 1 to message3.wav. I am looking for advice about the best way to accomplish that.

It seems like it should be possible using a combination of dmix, snoop, and dshare, as follows:

• Use dsnoop to split the 4-channel input to the crosspoint and another virtual sound input, call it "A".
• Use dshare to split "A" into four mono sources. Then can use arecord normally to capture wave files.
• Use dmix and possibly dshare to similarly let the crosspoint continue to use the multi-channel output while also providing a mono sound device for each channel that I can use with aplay.

Am I on the right track, or would I be better off adding functionality to the crosspoint application to read and write wave files? Thanks for any suggestions.

Unfortunately this won't work. d* plugins can have only hw type slave PCM. So, dshare cannot have dsnoop as its slave.

I recommend you to use simply JACK for such a purpose. It's exactly designed for this kind of work.

Takashi