[sdiy] analog pitch shifter circuit?

[mirwin at qouest.net]

Rohm produced a "variable speech controller" chip - the BA1701 - which 
was designed to be hooked up to a MN3004 and motor controller to 
implement the "speed up tape without changing pitch"  function on these 
old dictation machines - probably what was used in the Radio Shack unit.

It's easy to do real-time pitch shifting on most microcontrollers - 
circular buffer with separate read and write pointers and some 
rudimentary windowing - even a Sinclair ZX-81 with it's Z-80 processor 
can be used - but lots of processing power (eg. DSP chip) or external 
hardware is required for anything even remotely approaching 
"professional quality". By far the simplest and cheapest approach is 
just to get a used digital multifx unit - but if you enjoy building this 
kind of stuff, it could be a hobby all unto itself.
Regards, Mike