[Speex-dev] Fwd: Re: Fixed Point on wideband-mode: Single Frame loss on 2000 Hz sine causes "freak off"

Frank Lorenz Frank_wtal at web.de
Thu Feb 4 05:51:02 PST 2010

O.k., some more info:

I just tested bandwidth widening to fix this. But I need to go to gamma values below 0.9 to become stable -- clearly too much widening, I think.

I looked inside the Levinson-Durbin algorithm next. The lines

      r = DIV32_16(rr+PSHR32(error,1),ADD16(error,8));
      r = rr/(error+.003*ac[0]);

look interesting. While for floating point, .003*ac[0] is added to error, for fixed point, a constant value of 8 is added. When I alter this value, I get an output without "freaking out" for values 1,2,3 and 5. for 4, 6 and 7 the system is still instable.

I tired to change the line to 
 r = DIV32_16(rr+PSHR32(error,1),MULT16_16(ac[0],98));
but without success. Maybe, precision is too low...

Can you give me some hint how to proceed here?

best regards,

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