my opinion on this is a bit different - I recently 'filed complaint‘ ;-) with Carl about the previous audio clipping warning levels in DCP-o-matic. And as Carl is an audio buff himself, he acknowledged ;-)

Essentially, as digital cinema audio is digital, there should not be a ‚warning level‘ close to clipping - the signal is either clipping, then it’s bad, or it isn’t, then there is no technical problem. So, technically, until you actually hit 0dB peak (let it be true peak for now), you have no issue. In your case, you are just slightly above that hard limit, and that will lead to ‚clicks‘ in the audio. You should lower your overall (or, center level only) by -1dB to solve THAT issue. Technically, only -0.54dB would be necessary. But that difference is splitting hairs.

The problem here is mainly a psychological one - many people feel unsafe about proper audio levels in cinema. Anything indicating ‚OK‘ or ‚green‘ appears satisfying to them, anything ‚yellow‘, ‚red‘, ‚warning‘ makes them feel unsafe. In this case, only ‚red‘ is an actual issue (with the new recent thresholds in place).

I regularly analyze commercial trailers and movies with DOM. It is ‚the norm‘ that commercially mastered audio hits the 0dB mark peak (see screenshot below for a typical example). Again: Sample or true Peak at 0dB is not relevant as long as the level is set to precisely hit it, or stay just slightly below.

Wether the audio is actually 'too loud' or not - you can only judge that by listening to the sound in a properly calibrated cinema at standard playback level. More important than peak in that respect, but not easy to judge on, are the RMS and LUFS indicators. These are not ‚technical‘ clipping indicators, but they may indicate audio actually being perceived too loud in the cinema - but their numbers have to be weighted against the audio content they are being conveyed with. Is it a car chase, an earthquake, a music video, a nature documentation? How loud should a bird singing or a humming bee be perceived?

Now, LUFS, as currently used by DOM, is an absolute loudness weighting scheme from the broadcast/advertising domain, not the cinema. As such, it is not perfectly tailored for cinema use, but it comes closer than RMS or peak. You just have to know how to weigh the numbers. The proper method for cinema sound would be LEQ(M) - but we don’t have that for now. Common agreed upon max loudness numbers for cinema trailers e.g. would be 85 LEQ(M), for advertising 82 LEQ(M). As far as I know, nobody so far translated these LEQ(M) values to LUFS. And it wouldn’t be a straight forward translation anyway. There is a reason for LEQ(M), and a reason for LUFS. No one translates apples to pears. You can, however, analyze the same content with both methods, but their relation does not translate 1:1 for other content.

Now, from my experience, LUFS of -18.31 will not be perceived too loud in the cinema. That is within the accepted ball park. Also, from my experience, ‚around‘ -20dB RMS for center channel (that is usually dialogue) is okay as well. So, to me it seems you are still okay at that level. Though certainly near the top.

Very important, and many people have trouble to understand this: Neither 85 LEQ(M), nor ‚something' LUFS are TARGET levels. They are maximum loudness levels. They mean ‚no complaint‘ levels. No one can tell you how loud your sound should be in the cinema. Just as no one can tell you how bright the snow or how blue the sky has to be in your images. That is an artistic decision. Never AIM for 85 LEQ(m). Aim for never going higher than that if your mix is actually intended to be ‚loud'.

No one blames you for not hitting 82 LEQ(m). Unless your are doing advertising work, then you get fired if you don’t comply to the ‚we have to be as loud as everyone else' rule. Many people get this wrong and demand their film/short/doc mixes to be ‚at‘ 85 LEQ(M). THAT IS WRONG! Never demand that from a professional sound mixer!

Is that a dedicated center channel with dialogue, or did you put L+R summed up into C, or used the L/C/R upmixer? If so, you may not adjust the overall level, but only reduce the center level to fit within L/R properly.