Analog Pitch Shifter

robert bristow-johnson wrote:
(snip)

> not a particularly good pitch detector.   i wonder how to do an analog
> AMDF or ASDF circuit?  maybe you could have a circuit for each lag.
> then you need a way to pick the minimum lag.

> i dunno.  an intriguing concept (pure analog pitch shifter) that i
> hadn't thought too much about.  it looks to me that Vladimir has the
> simplest plausible concept of it.

Somehow this reminds me of:

http://en.wikipedia.org/wiki/SIGSALY

though it doesn't work quite the way I thought I saw it
described some time ago.

A pitch shifter using some number of narrow band filters,
amplitude detectors, oscillators, and voltage controlled
amplifiers would make a nice analog pitch shifter, though
fairly expensive.   Phase would be lost, but then it isn't
so easy to describe phase when doing pitch shifting.

-- glen

On Jun 2, 4:05 am, glen herrmannsfeldt <g...@ugcs.caltech.edu> wrote:
...
> Somehow this reminds me of:
>
> http://en.wikipedia.org/wiki/SIGSALY

wow.  that's an iteresting piece of signal processing history that i
never knew of.  (i knew there was some system used for the trans-
atlantic conversations between FDR and Churchill, and i knew of the
German Enigma, but not of this system).  look at what they were doing
in the early '40s:

SIGSALY has been credited with a number of "firsts"; this list is
taken from (Bennett, 1983):

   1. The first realization of enciphered telephony
   2. The first quantized speech transmission
   3. The first transmission of speech by Pulse code modulation (PCM)
   4. The first use of companded PCM
   5. The first examples of multilevel Frequency shift keying (FSK)
   6. The first useful realization of speech bandwidth compression
   7. The first use of FSK - FDM (Frequency Shift Keying-Frequency
Division Multiplex) as a viable transmission method over a fading
medium
   8. The first use of a multilevel "eye pattern" to adjust the
sampling intervals (a new, and important, instrumentation technique)


> though it doesn't work quite the way I thought I saw it
> described some time ago.
>
> A pitch shifter using some number of narrow band filters,
> amplitude detectors, oscillators, and voltage controlled
> amplifiers would make a nice analog pitch shifter,

instead of resynthesizing each component with oscillators and VCAs, if
you had enough narrowband filters, you could hetrodyne each output by
an amount that was proportional to the center frequency of each
narrowband filter (thereby bumping it up the same amount in log
frequency or "pitch").  there would be some inaccuracy of detuning for
frequency components that did not precisely hit the center frequency
of the narrowband filter it ended up in, but that's why you would need
a lot of them and very small bandwidth.



> though
> fairly expensive.   Phase would be lost, but then it isn't
> so easy to describe phase when doing pitch shifting.

phase is lost in any glitch-free frequency-domain pitch shifting
method (unless something tricky is done to somehow slowly bring the
phase of different components back in line).  time-domain pitch
shifters can retain relative phase of harmonics (sometimes this is
called "shape invariance"), but they can be glitchy if the input is
not sufficiently periodic.

r b-j