50kHz pitch shifter

[René Schmitz]

At 16:54 13.06.00 +0200, you wrote:

>Well, most probably the bat sounds are harmonic, after frequency
>shifting they will appear like noise... good for detection
>but not so good for sampling etc.

Well, I don't know how far the bat sounds go up in frequency, but lets assume 
a 50kHz pitch with overtones (100kHz, 150kHz ...). That converted with a
balanced modulator down to say 1kHz. Then the second (and subsequent)
harmonic(s) will be beyond the audioband after the downmix. So you get only
the fundamental. And the distortion of the harmonies is probably not a
problem since I'd expect that bats 
know little about scales. (The said applies to other ultrasonic sounds as
well, of course.)

I'd say, don't judge, before you had a listen. If it sounds crap one can
resort to other methods anyway.

About the sampling approach: When you play back at a lower speed you have
time-stretching. One could argue that this is a distortion, too. Think of a
bat flying by at snails pace... 

>right, recording natural phenomena , like the lake example.
>Use an ldr for sunlight detection etc. etc.

The IR-mic wasn't more than a photo diode run in current mode into the
inverting input of an opamp.

Bye,
 René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159