Re: An effect I've been working on (Ludger Solbach )

Subject: Re: An effect I've been working on
From:    Ludger Solbach  <ti6ls(at)TICK.TI6.TU-HARBURG.DE>
Date:    Wed, 19 Mar 1997 14:21:06 +0100

Regis Rossi Alves Faria <regis(at)LSI.USP.BR> wrote:

> The wavelet approach has several advantages over normal Fourier filtering
> since its filters have local support both in time and frequency,

Due to the uncertainty principle this ain't possible for linear
time-frequency distributions.

> making it
> easy to locate transients on some frequency bands.

I would say, locating transients within single frequency bands is a thing
one should not do at all, because it's the nature of transients that their
spectrum is local in time and spread over the whole frequency axis. This is
why transient detectors should rather watch out for such a pattern in the
time-frequency plane to gain maximum time resolution.
See http://www.ti6.tu-harburg.de/~ti6ls/research/ for intermediate results
of our work in this area.

[...]
> Curiously (or not, that's what I want to learn) the sounds (1) and (2) are
> virtually the same, with differences under the threshold of perception for
> some levels.

You did not say if you are using orthogonal or non-orthogonal wavelets. I
assume it's the latter, because in this case removing redundancy from the
coefficients would not have a very strong effect on the audible content
of the sound. In fact, this is even true for orthogonal wavelet expansions,
if you drop the right (i.e. small) coefficients. This is basically how
compression works.

Best wishes,

        Ludger.

---

 -----------  Ludger Solbach, Distributed Systems Department  -----------
|           Technical University of Hamburg-Harburg, Germany             |
|       e-mail: Solbach(at)TU-Harburg.d400.De, Tel.: +49-40-7718-3357       |
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