Re: [linux-audio-dev] Paper on dynamic range compression

From: Steve Harris <S.W.Harris@email-addr-hidden>
Date: Wed Oct 18 2006 - 12:54:54 EEST

On Wed, Oct 18, 2006 at 12:48:59 +0100, Dan Mills wrote:
>
> --- John Rigg <ladev@email-addr-hidden-man.co.uk> wrote:
>
> > If the control signal is derived from the upsampled
> > input
> > to the compressor, that is taken care of.
>
> But that puts potentially expensive gain calculations
> into the fast sr code, also I was rather planning on
> using the impulse used for the upsampler to provide
> the band limiting for free.

the gain calculations are relativly cheap, its converting those gain
levels back into a gain coefficient on the output that's expensive (from
what I remember).

the gain tracking is done per sample, but the cofficient calcualtion is
done every 4.

> BEAST was the project that had the SSE 2* up/down
> sampler code that seems to be reasonably quick.

But what interpolation function? If you something obvious and cheap you
may as well not bother, as you wont get accurate peak interpolation.

> The API is likely to be 'interesting' as most dynamics
> plugs don't generate an array of gain values then
> apply them, and a single sample streaming resampler
> doesn't bear thinking about.

I dont think a streaming resampler is more challenging than a correct one
that runs on buffers. You just have to preserve state with every call,
rather than at the buffer boundaries.

- Steve
Received on Wed Oct 18 16:15:03 2006

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