CALF limiter: oversampling?

[bluebell]

Hi all,

CALF limiter offers oversampling from 1 to 4. What is this good for? Does it process the signal somewhat cleaner? If yes, why? Do they interpolate somewhere?

[bazsound]

Im not quite sure, i just adjust it to what i think sounds better

[diizy]

Oversampling is pretty much exactly what it sounds like. The incoming signal is sampled several times for each actual sample.

This means if the incoming signal is 44.1khz, and you oversample at 2x, then the effect is effectively processed with 88.2khz samplerate, and the output signal is then interpolated back to 44.1khz.

Higher oversampling ratio causes higher CPU consumption, but also increased accuracy in processing.

[bluebell]

I think I found something explaining: http://www.fabfilter.com/help/pro-l/usi ... pling.html

So my conclusion is:
- Short lookahead AND medium or heavy limiting -> oversampling advisable
- Several ms lookahead AND no or only slight limiting -> oversampling not needed

I uses CALF limiter in each track as preamp/gain and "just in case" there could be some peaks. So oversampling is not needed in my case I guess.

P.S.: I like the CALF tools because of their graphical display. I can easily see overdrive levels and limiters' and compressors' gain reduction. That's a big help especially for beginners using those tools.

[AlexTheBassist]

Oversampling is something like antialiasing. It helps to lower or eliminate distortion in limited signal.

[ssj71]

Sorry guys, but I can help talk some science!

severely limiting/compressing a signal has the result of modulating the amplitude (or "size") of the signal. Amplitude modulation (similar to frequency modulation) creates "lobes" or copies of the frequency content on both sides of the original content, meaning it adds harmonics above what was previously there. So modulating a signal that is just under the nyquist frequency will result in creating frequency content above the nyquist frequency which of course aliases. The more/higher harmonics in your modulating signal the more that gets aliased, so heavy limiting is going to modulate the signal quickly (aka with high frequency modulation) aliasing a lot, softer limiting won't do it noticeably. So if it sounds bad in level matched a/b testing then bump up the oversampling. This effectively raises the nyquist frequency before the modulation without adding any frequency content to either of the signals, so once the modulation (limiting) is applied theres a lot more breathing room for harmonics to be added in without aliasing. These upper frequencies won't ever be heard by a human, and they get filtered out when downsampling back to the output sample rate which is much better than aliasing them back into the audible spectrum.

Ask me questions if it doesn't make sense. I LOVE talking DSP.

So, ya, exactly what everyone else said, with some extra explanation.

[lucianodato]

I requested this feature because of intersample peak distortion that often happens when heavy limiting takes place.

[bazsound]

I think I found something explaining: http://www.fabfilter.com/help/pro-l/usi ... pling.html

So my conclusion is:
- Short lookahead AND medium or heavy limiting -> oversampling advisable
- Several ms lookahead AND no or only slight limiting -> oversampling not needed

I uses CALF limiter in each track as preamp/gain and "just in case" there could be some peaks. So oversampling is not needed in my case I guess.

P.S.: I like the CALF tools because of their graphical display. I can easily see overdrive levels and limiters' and compressors' gain reduction. That's a big help especially for beginners using those tools.

interesting use but does it effect the recorded file or is it just inserted on the track and doesnt effect the recording.

ive wondered that, as if you use processing on anolugue inserts it gets to the recorder, is the same true for ardour

[bluebell]

It would affect recording if the signal went through an audio bus and the limiter was in the input-section, I guess.

But both with Qtractor and Rosegarden I record audio with Audacity while Qtractor/Rosegarden is playing the needed part in a loop. After recording I pick the best take in Audacity, save the wav-file and import it in Qtractor/Rosegarden. That's my personal workflow.