Film-Tech Forum ARCHIVE: Native Audio Input Levels for a DCP

This is topic Native Audio Input Levels for a DCP in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Grant Chambers (Member # 7051) on 01-06-2014, 09:05 AM:

Hello all! I am curious if anyone has a rough idea of what the levels (DB I'm assuming) need to be for a DCP. (input, from DCP itself, .wav files)

I make DCPs often. I use OpenDCP. The only real hassle that I ever come across is trying to figure out how loud my audio should be.

Here's a typical example -

I make a slideshow or intro of some sort. I use royalty free audio and crop it using Adobe Audition (not touching levels mind you). Upon ingestion and testing... WAY too loud. The fix is usually somewhere between dropping 10 - 15 DB.

It would just be great to have a consistent value to go by. I couldn't find any DCI specs on the matter.

Thanks!

Posted by Carl Hetherington (Member # 7107) on 01-06-2014, 09:38 AM:

To be honest I don't think you'll get a much better rule than "about 10-15dB". It depends on the nature of the audio that you are using, and in particular its frequency content and how much dynamic-range compression has been applied to it: these and other things will govern how loud it sounds.

There are various perceived-loudness measurements that you can do, but I think you'd do well to get reliably within 3dB of the "correct" answer without listening to the audio either on some speakers that you get to know, or in your auditorium.

Posted by Grant Chambers (Member # 7051) on 01-06-2014, 11:01 AM:

Thanks Carl. That's what I was afraid of.

Posted by Kenneth Wuepper (Member # 1174) on 01-06-2014, 12:01 PM:

Do you know what your metering system is looking for? In other words, are you mixing at -10 dBV or at +4 dBu for the system reference?

This could easily explain the difference in your recording level and the ultimate playback level in the theatre.

Posted by Steve Guttag (Member # 268) on 01-06-2014, 12:19 PM:

The issue is that music for normal playback and cinema audio are two different animals.

In order to have the volume capability need for explosions or other loud situations, in cinema one has to record 20dB down so that they have the headroom for the loud stuff. Remember, at -20dBFS, we have 85dBc (using pink noise...so there is a crest factor in there) in the theatre. Prolonged 90dBa levels will cause hearing damage. So think of dialog in the "average" seat as getting to around 80-85dB...a full 20-25dB down. Music and Effects have to be balanced with that (though they often are not). We willingly give up our noise floor in a theatre so we have that 20dB headroom given that even a quiet/empty theatre is going to be NC30 or louder...so there isn't really any penalty.

Now...lets look a music recording. That is completely different. One merely needs to keep the signal from clipping and then allow the maximum dynamic range to capture the recording. The end user will turn down the volume knob to what they feel is a "comfortable" or "appropriate" level.

This is NOT the case in a cinema...where a volume knob normally stays in one place for any given sound format...or in slicker systems, the volume may have a few presets to deal with LOUD TRAILERS and/or ads.

So, knocking the level down on a music (e.g. CD) recording so it is at a comfortable level in a cinema makes perfect sense. I would guess that 20dB down would be a starting point. If the theatre doesn't run their fader at 7.0 or 0.0dB...then you may feel the need to be a bit higher.