#39 Compressing, limiting, leveling

[Peter Verbeek]

Hi Jonas

Often I get a request from my users on automatic altering the volume (pre amp). Some want to level the volume from song to song or video to video so they don't have to dial up or down the main Windows volume all the time. And some want to compress the audio during a song or video making the volume less variable and more continuous on a fixed volume level.

In short compressing, limiting and leveling which is the realm of Equalizer APO which deals with the audio stream. I've tried to come up with solutions to these requests by automatically changing the pre amp but it doesn't produce a satisfactory solution (to slow amongst others). Is it possible to implement such features into Equalizer APO?

Links to requests:
https://www.youtube.com/watch?v=Gm-8W_R8kf0 conversation with SeenoChasm
https://sourceforge.net/p/peace-equalizer-apo-extension/tickets/43/
https://sourceforge.net/p/peace-equalizer-apo-extension/tickets/36/

[Jonas Dahlinger]

Yes, this is of course possible and I also remember multiple requests for these features. I thought that this missing feature would be resolved when VST support is available (which is what I am currently working on), but I can see now that this would not help Peace as it relies on builtin functionality.

Compression and limiting normally need some lookahead to work, so these filters have to introduce some latency. At least, the algorithms that I saw do that and that's another reason why I didn't implement them yet as I want Equalizer APO to have minimal latency. But maybe some latency is acceptable for the users.

By the way, you might already know that, but it is often better to try to eliminate volume issues using features in the playback software (e.g. ReplayGain or the dynamic range compression contained in Dolby Digital). Unfortunately, there seems to be no such thing for online video.

[Peter Verbeek]

I think you're right in saying that some latency is acceptable when a compressing/limiting filters is switched on. Such a filter always needs to look ahead also if it's a VST plugin. It's certainly something that can easily be explained to our users. Equalizer APO basic filters remain having minimal latencies.
Btw VST support is great. Do you have an idea of a timeline on investigating/building these features? No pressure :)

I must admit that I wasn't aware of features like ReplayGain and others. Although they aren't always system-width as Equalizer APO is, it's one of the things I can give as answer to questions on the subject. Thanks. It would be nice if YouTube had a built-in feature for volume/gain balancing. I'm always changing the volume while watching vid's.

[JP Hutchins]

VST compressors tend to model analog hardware compressors which of course have no look ahead or latency. There are modern digital implementations bit its not strictly necessary to introduce latency. For fun, leveling for cinema (where people conplain of dynamic range) can be tied to reading the level of the sub channel and and compressing all channels based on it. The important characteristic is a slow release in any dynamic range compression, even 1,000ms, 5,000ms and beyond IMO.

[Peter Verbeek]

Thanks for your contribution to this ticket. This could mean that a latency free feature can be created in Equalizer APO. Or perhaps a variation of features on limiting, compressing and leveling. Ones with a look-ahead (with latency) and ones without by using your suggestion.

[Bob Gonsalves]

We have a situation where we're playing back audio clips and a compressor would be useful to maximize the perceived loudness. Latency would not be a factor in this case.

[Peter Verbeek]

Thanks Bob for your example where latency isn't an issue. How are you now dealing with the volume difference in audio clips at playback?