> It is never stated what the first case ('num') is supposed to
> represent.
Hunh?? The very next sentences are:
"A value greater than 1.0 causes the sound to be transposed up.
A value less than 0.0 causes the sound to be reversed."
I'll add another example,
but there are dozens scattered around the *.scm files, and
in the src-channel documentation directly above src-sound.