[CM] adding an extra channel

[Bill Schottstaedt]

> but when I try to save the 4 output channels (as mono) the 4th one 
> doesn't exist ... 
>
> I guess maybe I should revert to Kjetil's suggestion? 

Yes, or try this sequence: open the 3 channel input file, use "New"
in the File menu, or (new-sound "test.snd" :channels 4) to open
an output file, select the new sound, call apply-ladspa setting
the sample-reader input sound to the 3 channel sound (via the
second arg to make-sample-reader) -- the 4 output channels
are being written, as far as I can see to the temp file (you can find
it wherever Snd is writing its temporary files).