50kHz pitch shifter

[Magnus Danielson]

From: Martin Czech <czech at Micronas.Com>
Subject: Re: 50kHz pitch shifter
Date: Tue, 13 Jun 2000 09:39:03 +0200 (MET DST)

> A related question:
> 
> When astronomers started observation out of the visible band of light
> (ie, infra red, radio, gamma etc.) they detected a whole new universe.
> 
> Now, would that be true for sub and super sonic?
> 
> It would be interesting to hear, what super sonic noise is on the
> streets...
> 
> I've heard of people recording sub sonic phenomena (water level of a lake)
> and play that back with higher speed. This is no problem, but some kind
> of DC sampling device is needed (most audio ADC are sigma-delta and have
> a zero at DC...)

There are still lovely linear ADs around. For instance, if you are not
very price sensitive (just play with the thougth ;) you could pick up
a system DMM, read out the samples from it over GPIB and dump it on a
hard disk. The benefit of this solution is that everything you need is
available on stock and add a few lines of code on the computer.
Naturally you can go much lower if you are prepare to do some work.

> And I've heard about people recording bats. Now , tape recorders are made
> for the audio band, they will not work. Same applies for most sampling 
> technology. Frequency shifting will destroy harmonic relationships.
> 
> Any ideas?

Now, let's first establish a few facts:

1) Wide bandwidth analog tape recorders have been available for quite
   long. For example, have you *ever* used a VHS? We are talking MHz
   of bandwidth here. For linear tapes is a 100 kHz within reach
   without too exotic tricks.

2) The actual bandwidth that you need migth still be quite narrow (10s
   of kHz).

The first fact is fairly simple, use a suitable tape recorder and you
can fetch the bats right away, no fuzz.

The second fact implies that you migth be able to frequency convert
the bandwidth of interest into the bandwidth available by the
recording device. Thus, a frequency shifter (really classic radio
frequency mixing) could very well be usefull.

> May be it turns out, that it is all boring.

Maybe so, but you don't know, do you?

> Another source of interest may be stellar sound sources (base band or 
> modulated).
> 
> http://www.marsmicrophone.com/pulsarsounds/crab.html
> 
> I'm also looking for some nice radio galaxies...

Far out, man!

Then, naturally you migth go inside... Brian Wilson recorded his heart
back in the 60thies for the Pet Sounds album, waaaay before young
Jackson.

Cheers,
Magnus