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EBU R128 compressor plugin?

Posted: Wed Sep 23, 2015 12:13 pm
by unfa
I've got an idea for something that might be useful, and make it easier to make audio content comply to EBU R128 loundess recommendation.

The idea is very simple: take a well known compressor and make it react not to peak or RMS but momentary LU value instead.

Why this is not already solved by regular compressors?

The idea is, that LU unit isn't the same as dB. The LU unit seems to take psychoacoustics and statistics into account, which is far more complicated than simple RMS calculation. Yet we have some great plugins by Robin Gareus that already calculate LU in realtime. If their analysis code could be connected to feed a compressor, we'd have a simple volume normaliser, that'd slowly turn volume up if we're below -23 LUFS, and down if we're above that, allowing the programme to sit close to the recommended -23 LUFS level easily. This is not gonna be possible with a standard compressor, as +10 dB necessarily equal +10 LU. I think the LU gain value for +10 dB gain depends on frequency content and absolute loudness (how far from 0 LU / 0 dB we are).

Some additional tuning might make this a simple EBU-R128 volume normalisation solution. I've heard this is done only by hardware devices that are very expensive. I guess we won't get perfect results, but still, this might be helpful for broadcasting and even mastering music.

What do you think?

Re: EBU R128 compressor plugin?

Posted: Tue Sep 29, 2015 12:05 pm
by emarsk
The LUFS measure is not actually that complicated: it's a couple of 2nd order filters (a shelf and a high-pass), a fixed gate, a windowing gate, and then an RMS measure on the sum of the channels. The specs are in this document.
Your idea should be easily implementable (but I'm not a programmer so don't look at me).
Meanwhile, you could approximate it by putting the EQs (the gates are not really needed for this) in side-chain to a compressor set to RMS. Finding the right attack/release settings could need some trying, I think.
It could be useful for broadcasting, but not for mastering, though.