[CM] [SND] How to split multichannel files into mono files?

[bil at ccrma.Stanford.EDU]

One way is to loop through the channels calling save-sound-as on each,
something like:

     (do ((i 0 (+ i 1)))
         ((= i (channels snd)))
       (save-sound-as filename snd :channel i))

where filename needs to be different for each channel.