Re: [linux-audio-dev] Another Annoying "How Do I Get Started" Question

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Subject: Re: [linux-audio-dev] Another Annoying "How Do I Get Started" Question
From: Steve Harris (S.W.Harris_AT_ecs.soton.ac.uk)
Date: Thu Jul 12 2001 - 19:05:56 EEST


On Wed, Jul 11, 2001 at 02:00:59PM -0700, Phil Burk wrote:
>
> ----- Original Message -----
> From: "Greg Berchin" <76145.2455_AT_compuserve.com>
> > >If you want to see this for yourself, take a GP implementation of a
> > >lowpass filter and turn down the turnover frequency to a few Hz, unless
> > >the programmer has been clever and sacrificed some quailty and speed
> > >the cpu use will go up by 40% or so.
>
> A jump in CPU usage may indicate that the FPU is getting numeric underflows
> which can interrupt the CPU! This can easily happen in IIR filters where the
> internal values decay exponentially closer and closer to zero. This can be
> avoided by adding very small values, like alternating 1.0E-26 and -1.0E-26,
> to the filter's internal values.

Thanks, but that is well known and easy to avoid, does the same thing
happen with large numbers?

I'm typically seeing it when testing with applyplugin which uses +-2^15 as
its 0dB value, and the code is written with +-1 in mind.

- Steve


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