It may be wrong, it may be not... Because it is not calculated from absolute min/max values in the source, but weighted and gated. So, if after a gain change certain signals fall below the FS referenced gating level, it may came out differently. I admit I guess I need to read it up somewhere.

BUT - I think, it is not correct to simply add/substract a gain change value, as it seems it occurs currently. Instead, the whole EBU R128 analysis should be performed again, I guess...? But that could be quite cumbersome in practice, because it usually takes quite some time.

• Carsten

From https://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP202.pdf :

'For differences between loudnesses, we use “LU”, so the difference between -23 LUFS and -21 LUFS is “2 LU”, not “2 LUFS”. Note that applying a gain of 1 dB to a signal will increase its loudness level by 1 LU. In that sense, 1 LU is equivalent to 1 dB.'

• Carsten

So do we think the current DoM behaviour is right?

I can not find a more official reference but this page https://ask.audio/articles/5-common-myths-about-loudness-metering-debunked states:

"The Loudness Unit (LU) is equivalent to 1dB—that is, an increase (or decrease) of one LU is the same as raising or lowering by 1dB. "

OK, thanks, I'll unhook this from 2.12.0 and we can give it some more time/thought.

I played with it a bit, and it looks to me as if DOM is behaving correctly for LUFS - the overall gain is 1:1 reflected in LUFS. I think this fails for extreme changes, if e.g. due to large master gain changes, some signals would rise into ungated range, or descend into gated range, changing the calculation. In these cases, the analysis should be performed again. But for the given purpose, it should be correct. I think the issue here is caused by signals with a very high dynamic range as we have them in cinema. Broadcast, the realm of R128, does not have that much dynamic and the purpose is more about centering practical signals around the target LUFS value.

If I edit the gain of an individual channel in the matrix, the analysis is reset and performed from scratch. That is correct as well.

Now, for LU, the problem mhm reports is correct. The relative dynamic range should not change with an overall gain change - within the same limits that I mentioned above. So, I think when doing an overall gain change, LUFS should change accordingly, but LU should not.

'The Loudness Unit (LU) is equivalent to 1dB—that is, an increase (or decrease) of one LU is the same as raising or lowering by 1dB.'

That is probably correct, but can not be reverted to express 'an increase by one or a decrease of 1dB is the same as raising or lowering LU by one.' That is clearly wrong.

-> LU should not change when adjusting master gain.

For practical means, we can not recalculate the full R128 with every change, because it takes too long. So I guess some simplifications should be allowed. This tool is to help, not to be an official R128 meter.

• Carsten

Maybe related to 0002647