I'm a little confused on the correct way to measure for and set the dialnorm metadata value when creating an AC3 for delivery to a client. Here's a scenario I just went through:
A month or two back, I did a 5.1 student film mix where the delivery requirements were just the trimmed/conformed stems. AC3 creation was to be handled by another department that was creating the graduation ceremony DVD with all the finished films on it.
Fast-forward to the graduation ceremony - the entire batch of final films is quiet as hell, probably in the range of 9dB below where everyone should be hearing them. The audience was straining to hear dialogue and even the big full-scale moments are registering like a Powerpoint presentation. A few mixers from the other films on that DVD that were in attendance confirmed that the same thing had happened to their mixes. It sucked.
As a few short films that had aired earlier in the ceremony (ones where sound people had created the AC3s) sounded fine (e.g. calibrated for 85), and I can't imagine whoever was running the booth just suddenly trimmed the entire playback system down in time for the main event, I suspect it was a problem with AC3 creation and the decode.
A few weeks ago, I do another mix where I'm responsible for delivery all the way through the AC3..
Disclaimer: this is my understanding of how the dialnorm value is handled on playback, and it's here that I would love corrections and notes. I hope that I am at least close to the truth.
The dialnorm parameter is used in the decoding process to adjust the mix's level appropriately for how the user's playback system is set up. The dialnorm value itself is, in professional cases, automatically determined by a Dolby hardware box/plugin whose algorithm can intelligently separate dialogue from the other sounds in the mix and spit out an average dialogue level for you. You key this in to your encoding software, make your AC3, and go.
What happens at the time of decode is that the entire mix will be trimmed to bring the encoded mix's specified dial level to whatever -27dbSPL is on the user's playback system. So if you key in a dialnorm value of -23, the whole mix is going to get ducked 4dB on playback for an unattenuated system. If the user's turned his system down by 6dB so he can have a conversation with his buddy while the movie's on, your mix will be dropped 10dB.
The decoder will not automatically boost the original signal no matter what the dialnorm was set to.
To avoid stuff playing back too quietly again, I decide to simply set the dialnorm metadata value at -31 (e.g. "don't adjust anything") -- even though I had mixed all the film's dialogue to average between -20 and -23. I was just scared of the decoder dropping my mix due to anything being set incorrectly and didn't want to take any chances. Also, delivery was happening at the 11th hour due to a last minute picture cut, so there wasn't time to burn a DVD and test playback before shipping this thing.
- Was this the right thing to do?
- Have you experienced similar horror stories?
- And how should setting the dialnorm -- and playing back the finished DVD -- go in a perfect world?
I'm still pretty new to deliveries and would love to hear this board's experiences. Maybe we can make this into a community post aftwards.