Average (RMS) Audio Levels

Catwell wrote on 2/22/2004, 10:54 AM

I operate a Museum Theatre and need to have the audio levels from each video at the same levels so that we don't destroy the hearing of our visitors or make the sound inaudible. I have produced DVDs from our sources and brought them into about the same range. We also run commercially produced DVD and the levels from these are all over the map. I have a seperate player for these with its own gain control.

I just received a MiniDV tape of a program that we will be running. The level is hotter than anything I have seen before. The issue is not so much the peaks, but the audio has been compressed so that the range is from -25 dB to -0.7 dBFS. To reach a usable level, compared to the other material I am using, I need to reduce the level by 9 dB.

Is there any standard for average level?
How do I meter an average level?
What is the best way to get there?

In addition to Vegas + DVD, I also am using Sound Forge 7.

Comments

busterkeaton wrote on 2/22/2004, 1:09 PM

I'm not an audio expert, but I think Normalize would be the way to do this. In Sound Forge you can set the level you Normalize to, to be -9db if you wish and use either peak or average RMS to do it.

Are you delivering on DVD? I have heard if you are delivering digitally you can normalize your peaks to 0 db or just below it. For VHS or analog sources, I believe you would want your peaks to be below 6db.

Spot|DSE wrote on 2/22/2004, 1:59 PM

>>>so that the range is from -25 dB to -0.7 dBFS. To reach a usable level, compared to the other material I am using, I need to reduce the level by 9 dB. <<<
then your other material is off the standard. You should be within 1dB of 0 for digital media. It's not like analog. You want maximum volume for maximum resolution. Otherwise, you are only throwing valuable bits away. Plus with this as a house standard, you'll quickly get up to par.
The easiest, but most expensive way to assure full level outputs on everything is to use WAVES UltraMaximizer. Best tool for mastering I've ever had the pleasure of working with. iZotope's Ozone has a nearly as good plug as well. then last in line is Sony's own WaveHammer, but that only comes with Forge.
Get those levels up for best results.

Catwell wrote on 2/22/2004, 2:58 PM

My existing material is peaking just under 0 dB. The problem is this new material is so tightly compressed that the average level is 9 dB higher when it is also peaking at the same level. The difference between the peak and average is much less on the new material. I need to find a way to determine what the average level is so that the different dynamic ranges do not move the average higher.

To determine the proper level I rendered a small section, containing peak material and dialogue, at 0, -3, -6 and -9dB. I then made a DVD of those renders and played it in the Theatre. The level that matched the existing material closest was -9dB. Is there a way that I can predict, without rendering, what the average level will be? Perhaps I should put another meter on the output of my sound card and set it as an averaging meter instead of a peaking one.

I would prefer to have a wider dynamic range than exists in my new video, but I don't know of any good way to expand an overly compressed track.
Watching the Vegas output meters on this video is very strange because they never seem to drop below - 20 dBFS.

Spot|DSE wrote on 2/22/2004, 3:51 PM

I missed the line about the other being so compressed. The only current way in Vegas, is to find an average level area, and highlight it/select it, and then look what's happening on the meters. This is still a strong argument in favor of the WAVES or iZotope tool, it will let you bring everything to a house standard at either average or peak level. It's pretty hard bringing back a compressed track without it sounding weird. You can play with 2 versions of the track using 2 different EQ's, and then mix the 2 stereo tracks down to one, and that will sometimes help, depending on how deep it went, but anything much past 4:1 is gone for good. This is a good 'fake' workaround...

Catwell wrote on 2/22/2004, 4:15 PM

Thanks for the help. I will look into the WAVES and iZotope tools.
I don't really want to change the video because it is someone else creation. I can justify tweaking audio levels because I would just have to do it with the theatre controls but I don't want to change someones work even though I don't agree with what they have done.

I think I will add some metering to my home (Vegas) system, so that I can correlate the levels there with what I see in the Theatre. The issue is to create a metering system that will always be reproducible and accurate. We are about to make serious revisions to our theatre programming so now is the time to create a consistant way of working.

Again, thanks for the advice. I am currently working through disk 2 of the Class on Demand DVDs and enjoying it greatly.

Jessariah67 wrote on 2/22/2004, 4:49 PM

Spot,

Have you taken a listen to Sonic Timeworks' Mastering Compressor? I'd be interested to know how you think it stacks up to the others you mentioned.

Spot|DSE wrote on 2/22/2004, 5:58 PM

I do have their mastering comp. It's quite nice. But it's not WAVES and it's not iZotope. I've got the whole Timeworks plug in pack. Their EQ is very, very nice.