wavchan, allchan - Determine the active channel(s) for I/O
short wavchan (WVFILE *wfp, short channel)
short allchan (WVFILE *wfp)
wavchan() sets the waveform associated with wfp to read/write
the requested channel(s). To choose all channels, channel should be
set to -1.
allchan() sets the waveform associated with wfp to read/write
all channels. (This is equivalent to wavchan(wfp, -1))
Returns the requested channel number on success or a -2 for an error.
H.T.Bunnell, Shirley Peters