True peak limiter options for Ardour

I know of Loudmax (native, closed source) and LSP Limiter (native & open source which includes oversampling modes). Are there other native and ideally open source options for TP limiting in Linux? Not that I’m disappointed in either but choice (like with reverbs) is always good given so much depends on the material.

From a recent email exchange. Emphasis is mine.

I realized during a choral recording project that the x42-Limiter was catching true peaks perfectly compared to Loudmax which was consistently overshooting. I was under the impression that your limiter didn’t have true-peak operation so how could it be doing this? Not that I’m complaining :wink:

That is probably a coincidence. While dpl does not oversample it has a short hold (low pass filtered peak) and assumes the worst. That combined with minimum release time may catch intersample peaks by accident if an earlier peak was higher than the intersample peak.

I believe that Loudmax even though it uses intersample peak detection uses a slightly different algorithm for limiting so apparently on loudness meters it is common to show as an over. They recommend lowering the threshold to -1.3 or 1.5 dB if the user absolutely needs a -1 dBTP reading! I just found this on the readme included with the download :wink:

Well, as I said, I’m not complaining. Your limiter is actually one of the most transparent I’ve used for classical for when a couple of dB need shaving off the top. Default settings too!

I found where I got the information in my email from. This is directly on the Loudmax site (latest version 1.35):

ITU-R BS.1770: There are coefficients given in this recommendation for the calculation of inter-sample peaks. Unfortunately these coefficients do not seem to be optimal for limiters. They have a negative effect on transients and lead to high overshoots in true peak meters that use higher quality upsampling. Therefore LoudMax uses optimized coefficients that do not affect transients and reduce the overshoots to similar values with all true peak meters tested. The downside is that BS.1770 calibrated true peak meters will also detect overshoots of up to 0.2 dB with LoudMax ISP detection. So if you need to guarantee a true peak level of -1.0 dB for example, set the output level to -1.2 dB or even -1.5 dB.

This is also a good read:

Interesting that they think Sequoia & Samplitude avoid inter-sample peaks by simply reducing gain post limiting. They even compliment the method as “a great way to handle ISP”. The downside, as they point out, is that the master is going to be -1dB lower in volume i.e. you’d need to overcompensate on loudness to conform to a certain integrated value.

As it turns out, I don’t think I’ve ever managed to overload Loudmax when using inter-sample peak mode but I’m not exactly slamming my choral recordings like they are a Metallica track :wink:

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