Quick question on audio levels for mixing an event DVD

[Dave Largent]

Originally Posted by Fred Retread

I think you must have meant 24dB dynamic range?

This is what I was thinking, too. If you are keeping average
levels around -12dB, then you have 12dB dynamic range above
that, and 12dB (or thereabouts) below, so that means you
have 24dB of dynamic range.

I see how Douglass' definition of "lowest to highest" is
"dynamic range", but here we're talking
about "average level" being -12dB, not lowest level being
-12dB. So, if you're average level is -12dB, shouldn't your
dynamic range be much more than 12dB?

[Douglas Spotted Eagle]

Originally Posted by Dave Largent

I see how Douglas' definition of "lowest to highest" is
"dynamic range", but here we're talking
about "average level" being -12dB, not lowest level being
-12dB.

It's not my definition, it is *the* definition.
"Dynamic range describes the ratio of the softest sound to the loudest sound in a musical instrument or piece of electronic equipment."
"A workable definition of dynamic range is the ratio of the highest (lightest) signal which a scanner can record to the lowest (darkest) signal..."

[QUOTE=Dave Largent]So, if you're average level is -12dB, shouldn't your
dynamic range be much more than 12dB

Yes, and no. If your average is -12dB, and you have an upward swing of 14dB, then you would be +2dB over 0, but there is no +2dB over 0dBFS, which is the point I'm putting across (and apparently badly, if it's not being understood). Yes, you have a dynamic range which may or may not exceed or be equal to 24dB with an average of -12dB.
I can't speak for anyone else, but I'm more about peaks and keeping my average slightly hotter, which is why good compression is important to me. I'd much rather have a slightly hotter signal with light compression on the top than leave a lot of bits on the floor simply because the source wanted to get loud for a passionate moment.

Remember, while acquisition is different than delivery, you can never recover lost resolution, and it's all about using up those numbers. Why go 30 in a 55 lane?

I'm sure others feel differently about it, but that's my method of working.

[David Ennis]

Originally Posted by Patricia Lamm

...I think my confusion at this point is more one of terminology...When someone says they keep their average levels at -15 dB, are they referring to an RMS of -15 dB over the entire sample?...

They simply mean that they set their levels so there is about as much content over -15 dB as under -15 dB. At least, that's what I mean. "RMS" does not have any meaning with respect to dB, which is just a way to express large ratios with small numbers.

Originally Posted by Patricia Lamm

...(I know they don't really mean 'average' because that should be -Inf, right?)

You are correct that -15 dB is not the arithmetic average of the actual signal that ranges from, say, -25 dB to -5 dB. But you are in error about -Inf. That woudl equal a voltage level of zero.

[Dave Largent]

Originally Posted by Fred Retread

They simply mean that they set their levels so there is about as much content over -15 dB as under -15 dB. At least, that's what I mean.

Yes, that's what i mean when I talk about having
an average dB level.

[Dave Largent]

Now, here's what I was wondering about (in my
original question): If I will run into any trouble
by making a DVD with a dynamic range of
from -3dB to -21dB, which is 18dB range.
Now, Douglass says TV only has a range of 8-10dB.
Why is TV's range so low? And how will this
work out with making a DVD (with a range of
18dB) for TV play?

[Patricia Lamm]

Thanks for the clarification about 'average levels'. This has also become more clear to me after downloading Ozone 3 today -- great program -- the meters and graphs in Ozone 3 seem to provide more understandable information (to me at least) than I was able to obtain from Sound Forge alone.

Originally Posted by Fred Retread

You are correct that -15 dB is not the arithmetic average of the actual signal that ranges from, say, -25 dB to -5 dB. But you are in error about -Inf. That woudl equal a voltage level of zero.

I guess I'm speaking more as a mathematician when I say this. If the signal has correct DC-offset, then the mathematical average should actually be -Inf, yes? (The statistics tool in Sound Forge confirms this -- it reports the "average" to be -Inf in both channels.)

[Douglas Spotted Eagle]

Originally Posted by Dave Largent

Now, Douglas says TV only has a range of 8-10dB.
Why is TV's range so low? And how will this
work out with making a DVD (with a range of
18dB) for TV play?

It's not a question of TV having a low dynamic value, it's the range in which the levels are kept deliberately. Too loud, everything becomes squished down at the broadcaster anyway. Too soft, the viewer can't hear and they turn up their set, but when a commercial comes on it blows them out of their seat. Stretch it as far as you will, but realize that if it has too much dynamic range from actual audio to loudest point (meaning from most quiet sound you want audible vs silence) then you'll either have viewers straining or recoiling. This is another benefit of 5.1, of course, is you can have a mix with much more happening, since the dialog is usually in its own channel, and you've got more locations for sound sources.
Borrowing from Murch, when we started working for theatre, we built a "popcorn loop" just like they did for Apocalypse Now, and still use today. It really helps you figure out what is being heard where when you've got that sort of a source. In a theatre mix, you can have monstrous dynamic range. Too much. But, most mixes are kept to the 20dB range. As I mentioned earlier, Walter Murch, Brian Keane, and a few other mixers are pushing 25dB worth of range. Dynamic range is abused by most engineers, both in video and music industries. Pushing everything hot doesn't leave the viewer any space to breathe and you'll wear their ears out and they become numb. Too much range, you'll leave them straining to hear, but recoiling when you make a punctuation mark. back to the original question or point...Television *can* offer a broad range. But the question isn't how broad it is or isn't, it's how audible or listenable the audio becomes if you stray too far from general standards. Experiment, it doesn't take long to figure it out.
Bear in mind as well, now we're talking about delivery, which has very little to do with acquisition. It's much easier to record a solid signal and pull it down in post than it is to record a quiet signal and attempt to recover it in post.

[Emre Safak]

I thought Dynamic Range Control in Dolby Digital existed to address this problem.

[Douglas Spotted Eagle]

Originally Posted by Emre Safak

I thought Dynamic Range Control in Dolby Digital existed to address this problem.

Do *you* want to control what the viewer hears, or do you want metadata embedded in the stream to instruct whatever variable their playback device might have to deal with it?

Once you start undergoing the process of submitting audio to Dolby to be certified, you quickly start figuring out means of circumventing the process as much as you can.
LFE management, Dialog management/normalization, equalization, etc are all bypassable to a limited extent, but yes, you can ignore it all and allow your encoder to deal with it for you via the metadata inserted and processing. Most engineers prefer to not do it that way, but it is there if you want to fall back on it. Kinda like having an auto TBC for your video though, and you never know for sure what the results might be. It might not be that important to you though. Some folks are thrilled at their mixes on plastic computer speakers and they're very happy with Radio Shack mics, too. It boils down to what you're happy with and what you're exposed to.