Does anyone have an idea exactly how discontinuous it should be to be heard?
When I did my DFT modification with OLA it's usually 50% overlap of 1024 (or
above) point windows Hann or Hann/Hamming or the like. I never heard a click
or pop. I gathered that as long as it was properly windowed the OLA would
not incur discontinuities that were not already there in the middle of a
frame. Is that right or wrong?
-----Original Message-----
From: Theo Verelst
Sent: Sunday, March 24, 2013 4:28 PM
To: music-dsp@music.columbia.edu
Subject: Re: [music-dsp] Strange problem in fixed point
overlap-addprocessing
Hello all,
I am experiencing a quite frustrating problem these last few days
and I was wondering if anyone has any ideas on how to tackle this.
I am developing a speech processing algorithm on a TI C5515.
First I though you might be working on one of those great superfast TI
8-core dsp boards, but then I read "speech coding" so I suppose it is
more phone or usb stick internet phone stuff..
Interesting subject, of course there are a number of generalities when
working with speech coding (as far as I know it) and FFT based filters:
Robert already indicated the buffer length and processing pipeline
filling issue: when you start out, it will take a while (in almost every
practical case) for your FFT computation to get a result, which then
suddenly appears, hence causing an abrupt change in signal (click).
Of course when you talk about a "real value changing the gain of a set
of FFT transform outputs", you multiply both the REAL and the IMAGINARY
part of the those FFT transform output tuples ? Otherwise you'd change
the phase of those frequency measurements.
Finally, if you use averaging of either the FFT frequency/phase
information or the frame of inverse FFT values based on one se of bins,
you have to decide wether that averaging should be done one a sample for
sample shifting and averaging, or purely frame based, because in case
you multiply one frame of either FFT transform values, or the
back-transformed (to time samples) frame, and the next frame gets a
different amplification factor, you'll hear a discontinuity, just like
when you'd suddenly change volumes with no smoothing!
Theo V.
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