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Re: Removing transients in rejoined speech files

Dear Allan (and Pawel),

simply joining at zero crossings brings NO guarantee that you won't
have click artifacts. If I take a sine wave and I cut it off at the
zero crossing then I still have a 'sharp edge' at the zero crossing
point where the signal snippet ends abruptly, and this will produce
'spectral splatter' and hence a potentially audible click artifact.
You cannot completely avoid such transient artifacts at the joints of
your cut and shuffled samples, but you can reduce them very
considerably by cross-fading, and using something like a raised cosine
ramp is likely to be better than a linear ramp.
You are basically dealing with what signal engineers call a
'windowing' problem, and the literature on this is vast, so we could
debate endlessly on what the 'ideal' approach would be, but a 3 ms
cross-fade, as Pawel suggests, is likely to work well enough and is
unlikely to raise too many eyebrows among potential reviewers.


On 04/12/06, Pawel Kusmierek <p.kusmierek@xxxxxxxxxxxxx> wrote:
Allan J Goldstein wrote:
> I have tried looking for zero
> crossings and making the cuts at these points, but
> there is still the interference.

Cutting at zero crossings should solve the problem... But, do you just
check for zero crossings, or for zero crossings in one direction? I mean,
if you do one cut at a zero crossing where the signal goes from negative
to positive, and the other one where the signal goes from positive to
negative, then you can get a strong transient in a rejoined file: the
signal will "bounce" from the zero line.

If this does not help, about a short (1-3 ms) crossfade - unless it
interferes with your purpose.


Pawel Kusmierek PhD
Department of Physiology and Biophysics
Georgetown University Medical Center
The Research Building WP23
3970 Reservoir Road NW
Washington, DC 20007
phone: +1 202 687-8851

Dr Jan Schnupp
University of Oxford
Dept. of Physiology, Anatomy and Genetics
Sherrington Building - Parks Road
Oxford OX1 3PT - UK