RE: Sound

Hey,

I toyed with using a "sliding mixer", although at the time I didn't know
what it was called. I noticed it would work on most cases, but as soon
as you approached an area with tons of explosions and gunfire, and then
you moved into an area that was quiet, the music was noticeably louder.
I'm toying with the idea of using the slider based off of distance as
well as sample amplitude. I'll let you know how that goes!

I still haven't been able to find anything about this on the web, even
though I have found a ton of pages about DSP and how to use FFT and all
that fun stuff, none of them had any reduction mixing algorithms that I
could find.

Thanks
-Ken Noland





-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Brian Hook
Sent: Monday, May 16, 2005 1:46 PM
To: [email protected]
Subject: re: [GD-General] Sound

> IIRC what you're looking for is called "cross normalization". You
> don't average (add all channels together and divide by the number
> of channels) because dead channels will attenuate the output too
> much;

The other issue is how large a window you perform these operations on. 
 Clamping can be done per-sample-slice, but if you average per-sample 
then your volume is going to be all over the map.

>  Instead you add the absolute values of all the channels
> together (pseudo envelope) and then normalize each channel against
> this absolute value. To improve dynamic range this should be done
> on a logarithmic scale.

This is the similar to "riding the mixing slider", which works, but 
requires a lot more computational effort as you keep track of a 
sliding window and perform the normalization (via table lookup 
hopefully), along with a global volume atenuation.

Unfortunately it's still very susceptible to heavy transients, but at 
least loud sections get compressed down.

Something else to look at are compression/limitation DSP algorithms.

Brian




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