Re: An effect I've been working on (Jont Allen )

Subject: Re: An effect I've been working on
From:    Jont Allen  <jba(at)RESEARCH.ATT.COM>
Date:    Wed, 19 Mar 1997 15:14:06 -0500

Ludger Solbach wrote:
>
> 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       |
>  ----------------- http://www.ti6.tu-harburg.de/~ti6ls/ -----------------

I very much agree with the above coments.
Jont Allen