[linux-audio-user] creating harmony files ( 3rd, 4th, 5th)

[ed orphan]

Can you create a file that is the 3rd, 4th, or 5th
harmony to another file using Sox or ecasound?
I've got a nice riff in the file  riff.wav and I'd like
to create some files that are in harmony to that file.
So I'd have a file called riff_3.wav that would be
in 3rd harmony to the riff.wav, and one called
riff_4.wav that would be in 4th harmony, riff_5.wav,
etc. Then I'd like to combine these files in various
ways to create an output.wav. just to experiment and
see what happens. Can you do this using Sox or
ecasound?  Could anyone tell me how, or where
I could get some examples or more information on
how to do this?