This is a not-quite-technically-correct stereo
frequency shifter (with separate controls for the
left & right channels) based on techniques seen on
this web page:
The reason for this not being
technically correct is that doing this the right way
would require a lot more CPU. This implementation
only achieves true frequency shifting in a certain
range of frequencies, while frequencies outside of
this range get an effect closer to ring modulation,
which is still interesting.
There is also a simple distortion
effect and LFOs for modulation.
(no longer exist)