[speex-dev] integerization

Christian Buchner Christian.Buchner1 at epost.de
Fri Jun 27 02:10:22 PDT 2003

Hi there.

Just a little status update how that integerization is coming along.
I am trying to limit myself to 32 bit arithmetics. That means
not using any __int64 or long long datatypes at any point.

I have now replaced all steps up to including the estimation of
the LPC filter coefficients with integer code. That is about a
quarter of the total work completed, I would say.

One problem that i encountered is the high dynamic range of the
results of the autocorrelation function. Think 96db squared.
-> 192 dB ;) That is not very desirable when used as input for
further processing.

I have most precision issues pretty well under control until before
I enter the Levinson Durbin algorithm. The Levinson Durbin routine
is where things go bad. I am currently losing 2 dB of SNR when I
apply the integerized version. The algorithm seems very sensitive
to rounding and precision issues.

Is there a way to alter the algorithm or to condition the input
values and intermediate results such that the outcome is not quite
as sensitive to computation with integer arithmetics?
Do we have some of the maths/signal processing gurus here who
could provide some clues?

I may decide to postpone "fixing" this routine and proceed
with my integeization quest. Just like most politicians do:
Leave a mess and quietly return to business. ;)


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