Sound normalization?

[Sastraxi]

I've build a mythtv pvr box, and it's doing great. There's one thing we'd like to see though... real-time volumen normalization. Is there something that can do this? It's a pain watching movies or TV shows and having to adjust the volume every 10 seconds (for example, the Indiana Jones DVD has parts where it's fine at "volume 10" and too quiet at "volume 30"!)... maybe some sound server can do this?

[Kristleifur]

Have you seen ReplayGain?

foobar2000 for Windows uses it. Maybe there's a media player that does, too.

[Sastraxi]

The problem is, I'm looking to normalize live input.

[Woody]

Normalisation only makes sense on the whole...i.e. you normalise
a complete wav by analysing the whole thing. What you really want
is very agressive compression.

[Sastraxi]

I'm looking for something that will analyse the output from /dev/dsp. If it goes above a certain decibel level (after volume controls are changed) for too long, it will adjust the volume controls.

Perhaps I could use C++ to do this; seems like an interesting project!

[Kristleifur]

You just reinvented the compressor, basically :)

While there is a subtle and useful difference what you're talking about and a classical compressor, I really encourage reading about the techniques of compression and limiting.

Good places to start might be http://sospubs.co.uk, http://em411.com and maybe http://futureproducers.com. There are probably others. Actually, http://hydrogenaudio.org probably has something, too.

If you'd describe what you want to a sound engineer, he'd probably give you a compressor with really long attack / release times.

There is a good chance that something useful might be available for Jack (ebuild: jack-audio-connection-kit).

[Sastraxi]

Thanks for the reply Kristleifur

I figured that I'd probably stumbled onto something that had been done before, and having done a few (not many mind you) recording sessions with my brother's band, I've got a fair idea of where I could be headed with this.

I'll look up Jack; perhaps I can get it to fit my needs.

[Sastraxi]

Okay, I'm going to get jack audio connection kit, jack rack, the plugins from "Steve Harris" (which includes several low-CPU configurable compressors ), and libjackasyn to allow MythTv to become a Jack source....

Heh, this is gonna be great

[Kristleifur]

Please keep us posted. I never get around to playing with jack, as I intend to. Stories would be appreciated.

[Sastraxi]

If you guys are still interested:

MythTv supports ALSA now Which means that it should be working with the standard alsa-lib output to JACK bit. However, I haven't taken many more steps with it. Before I had used jacklaunch (from ebuild: libjackasyn) to connect; it wouldn't be able to do the TV bit (it crashed), and music would go through just fine (although the compressors did get very low quality on the output from jacklaunch... who knows).

However it should be completely doable at this point!

[Kristleifur]

Cool. I have got to get around to setting up Jack and all that nice audio stuff on my machine.