[LAD] Mixing audio: Noiseless volume changes

[Harry van Haaren]

On Mon, Mar 18, 2013 at 11:45 PM, Fons Adriaensen <fons at linuxaudio.org>wrote:

> A critically damped
> second order lowpass with a rise time of 30 ms or so will eliminate all
> audible artefacts. It's very low on CPU and you only need to run it while
> the gain is changing.
>

Although I understand the words & their meaning, I have no idea how to
start implementing such a filter.
I've found a 1st order algorithm on musicdsp:
http://www.musicdsp.org/showone.php?id=257
Since its second order I understand it needs the previous 2 outputs.
Critically dampened implies that the "factor" of influence of the previous
samples is very close to 1 ( 'a' in the algorithm linked )

How is the "rise time" determined here?
Noobie questions :) -Harry
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.linuxaudio.org/pipermail/linux-audio-dev/attachments/20130319/13645cfd/attachment.html>