pitch shifting....the analog way???

[Martin Czech]

Again trouble with this fu... mail.
Maybe some control character in it.

Sorry for the fuzz.

Let's try it this way:


I'm no expert, but I'll try:
First the easier:

Flanging:
Flanging was first done with tape recorders. The same recording played
back on two machines, and the reels (there comes flange-> flanging)
"controlled" by hand, ie.  speeded up or slowed down. So flanging is:
mixing the original signal with a time delayed version, and the time delay
varies. The delay has to be short, a few ms, otherwise the signals will
loose their correlation. So no echo is heard. The delay is constant for
all frequencys, which will give a specific pattern of notches, ie. some
frequencys are attenuated, other's are emphasized.

Phasing:
Phasing was done with analog phase shifter networks, there's also a delay,
but the delay is FREQUENCY DEPENDEND. Mixing the phase shiftet signal
with the original gives also notches, but with a different pattern.

Ringmodulation:
Basically four quadrant multiplication. This was your proposal.
Multiplying a signal with a sine wave gives two side bands.

And Frequency shifting:
Via single side band modulation (done via an arrangement of
ringmodulators), the frequency components of the incomming signal are
shiftet up/down a fixed number of Hz. This will change the harmonic
relationsship of the signal.  If you take e.g. a saw wave with 100 Hz,
there are partials with 100, 200, 300... Hz. If they are shiftet by 10
Hz you get: 110, 210, 310 ... Hz. This is no harmonic wave any more. Same
apllies to chords etc.

Pitch shifting:
The basic idea is to have the same effect like a slowed down/ or speeded
up tape, but with NO inluence on the time.  You want to multiply the
frequency of your signal components with some factor.  Ie. harmonic
relationships are kept.  The principle of operation can be understood
from the first implementation: a rotating head tape machine. While the
tape moves on with mormal speed, the relative speed from heads to tape
is influenced by the rotation of the four head assembly. Of course, if
one head leaves the tape and the next comes in, there are artefacts.
This time domain principle (no matter with tape or digital storage)
produces distortion of the envelopes., large pitch shift results in
echoic effects.

One can do pitch shifting also in the frequency domain, transform, shift
the components and retransform. Higher quality algorithms work this way,
there are no audible artefacts for decent shifts up/dowm a fifth.

m.c.