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: Wed Jul 11 2001 - 18:35:45 EEST


On Wed, Jul 11, 2001 at 09:22:36AM -0400, Greg Berchin wrote:
> Benno Senoner wrote:
>
> >I do agree that these days it pays off to use a general purpose PC to
> >perform dsp stuff rather trying to build expensive custom tailored hw
> >solutions.
> >Especially now that almost all CPUs do have SIMD instructions.
>
> Even without SIMD, GP processors are getting so fast that DSPs are no
> longer the only game in town.

Speed is not the only advantage of DSP chips (though bear in mind that DSP
chips get faster as GP chips do, the're still quicker at number crunching).

The advantage of DSP chips is that all operations take one cycle,
regardless of parameters. This makess it possible to write code that you
know will always complete in the time constraint. Some GP operations (eg.
multiply) take a variable amount of time depending on the parameters.

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.

Also, although modern x86 chips have SIMD instructions, gcc won't generate
them (maybe in 3.0, I haven't checked), and the ones useful for audio
can't even be inlined with asm() yet (ditto).

That said, a modern GP chip is a very cheap versatile device, and easily
capable of realtime audio work.

- Steve


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