50kHz pitch shifter

[Martin Czech]

The argument is correct. Extreme Pitch shifting would be good,
but that has artefacts, too.

I would assume that bat do sinoidal packets (high energy, narrrow
bandwidth) or fm chirps (Doppler ;->).

Ok, lets get off the bat track, maybe there are other ultra sonic source
as well in the streets.

m.c.


:::X-Sender: uzs159 at mailout.uni-bonn.de
:::Date: Wed, 14 Jun 2000 15:14:13 +0200
:::To: Martin Czech <czech at Micronas.Com>, synth-diy at node12b53.a2000.nl
:::From: René Schmitz <uzs159 at uni-bonn.de>
:::Subject: Re: 50kHz pitch shifter
:::Content-Transfer-Encoding: quoted-printable
:::
:::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
:::
:::