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Re: making a sound unrecognizable

You could try a simple "speech scrambler" approach.  You
multiply the signal by another wave.  The simplest approach
multiplies by a constant sine wave that is in about the same
frequency range as the signal.  This uses the relationship
that the product of sinusoids gives sum and difference
terms, so the incoming spectrum is split at the multiplier
frequency and the two portions are reversed spectrally. More
complex scramblers can use a time-varying singal as the

But we get a lot of cues from envelopes, and this approach
preserves the envelope.

There is also the larger issue of what is "acoustically
similar" yet still different.

Best regards,

Bob Masta


On 12 Sep 2006 at 18:26, Ursula Kirmse wrote:

> Dear list members,
> I'm looking for a possibility to change/edit a environmental or at least 
> natural sound in a way  that it is not any longer recognizable as what 
> it is, but, however, for doing this with changing as less acoustic 
> parameters as possible. ;-)  The intention is to use these sounds in a 
> MMN paradigm and it is important that  both "versions" of the sound are 
> acoustically as similar as possible.
> The main point is that the sound (that can also be a more complex thing 
> as the sound of a barking dog or a something like that) should be not 
> possible to be recognized as what it is.
> I would be very happy about ideas or would like know if maybe somebody 
> has already tried something like this?  I would also be very happy about 
> recommations for software or matlab scripts that could be helpful in 
> respect to this. For example I'm looking for a way to transfer the 
> amplitude envelope from one sound to another (I already wrote a matlab 
> routine for this, but its not yet functioning perfectly fine and the 
> result is not completely convincing).
> So if anybody has a an idea I would be grateful.
> best regards and thanks a lot,
> Ursula Kirmse
> -- 
> --------------------------------------
> Ursula Kirmse
> University of Leipzig
> Cognitive & Biological Psychology
> Institute of Psychology I
> Seeburgstrasse 14-20
> 04103 Leipzig, Germany
> Phone +493419735978/Fax +493419735969
> --------------------------------------