Any tips on mixing for DOLBY SR?

[matotas]

Hello!
I`m currently working on a 2-track mix for film. My final product (a quicktime with stereo 48k 16bit audio)will then be transferred to DOLBY SR. Since this is my first time working with film I just wanted to know if you guys have any tips, comments, recommendations for my mix. Also, does anyone know what exactly dBFS (Full Scale) means, is it RMS?
Thanks a lot....

[Charles D. Ballard]

Also, does anyone know what exactly dBFS (Full Scale) means, is it RMS?
Thanks a lot....

No it is not RMS. Remember that dB is a way to measure sound level in reference to a fixed level.

In the air we measure pressure waves against a fixed preasure:

dB SPL= 20 log P/P(ref)

P = sound pressure in dynes/cm2
P(ref )= 0.0002 dyne/cm2 (the threshold of hearing)

On a wire we measure current or voltage levels against a fixed level:

The basic formula is: dB = 10 log P/P(ref)

P = power in watts
P(ref) = reference power

But it’s a little more complicated here. You need to know what you are referencing so we have dBm, dBu, dBv or dBV:

dBm = 10 log P/.001 (P(ref)=1 milliwatt)
dBu or dBv = 20 log V/V(ref) where V(ref) = 0.775V (0dBm @ 600 Ohms = .775V)
dBV= 20 log V/V(ref) where V(ref) = 1 volt.

In the digital world we measure bits against bits.

dBFS = 20 log SL/FS

SL = Sample Level, a binary representation of the sample level
FS = Full Scale, a binary representation of maximum possible SL (all bits=1)

For example, on a 16-bit system:

20 log (1111 1111 1111 1111 / 1111 1111 1111 1111) = 0 dBFS
20 log (0000 0000 0000 0001 / 1111 1111 1111 1111) = -96 dBFS

Because it is impossible to have a SL above FS dBFS will never be above 0.

I know this may be more than you asked for but I hope it helps...

[Richard Fairbanks]

Of course you will fully read and understand the room calibration and setup sticky thread at the top of this forum, and have your properly level/eq calibrated speakers as per standards.

As far as Dolby SR, or Dolby Surround, search this forum for "Pro Logic" and/or "steering chip" (including the quotation marks) and you'll find some good reading about the matrix encode/decode that is part of Dolby SR. It is not like listening to discrete channels! If you are mixing with only two speakers you cannot judge the panning at all and may be in for quite a shock when you hear your mix played through a Dolby SR 4.0 surround system.

[Charles D. Ballard]

Hey Richard, I love the antique page on your website!

[Richard Fairbanks]

Thanks!

[minister]

to add to what charles (hey thanks for puting it all in one place!) and richard said:

the SR plays off of analog optical on the film, so you need to be very careful with levels. meaning, you cannot run it as hot as an SR•D (dolby digital surround) or your radio ready CD mastering job. what happens when your mix verges on and goes into overmodulation is you get either very nasty distortion or a complete drop out of sound. a good stratgey is to maximize your frequencies and make sure you have a good balanced mix with everything in its place.

not to be redundant, but dBFS is your digital FULL SCALE, as represented by the meters in you PT system. 0dBFS is clipping. -.2dBFS is just under. setting your sytem up to be calibrated to -20dBFS means that the meter reads -20 on your PT sytem. ***YOU WILL READ THE CALIBRATION THREAD AT THE TOP OF THIS FORUM??!!*** your meters in PT are peak meters. they tell you, instant to instant, where the peaks are. RMS is Root Mean Square, which is a fancy, mind-befuddling formula for calculating what could be loosely called AVERAGE level, or power. your ears do not hear "peak to peak", but they do hear what is represented in RMS values. RMS is useful, especially in a film SR mix, because it will tell you the perceived loudness of something. the peak meter will tell you that you are or are not going into the danger zone.

[Charles D. Ballard]

to add to what charles (hey thanks for puting it all in one place!) and richard said:

You're welcome!

I moonlight as a DJ and wrote that for another forum where they (a group of DJs) were having a bit if difficulty understanding their meters and all those specs they get on their marketing literature. I just cut-and-pasted it here.

[minister]

hunh, dj's mixing in SR! what's next?!

I just cut-and-pasted it here.

and here i thought you were a Random Access Memory blustery suede ineffectual, and i find you are just an e-litist

[Noiz2]

Terminology question.

Isn't Dolby SR strictly a noise reduction process. As far as I know it is separate from Dolby Stereo (surround) except that it is included in the Dolby matrix box. I know that I can SR encode non surround tracks so I'm confused by the use of SR to indicate surround.

Of course you will fully read and understand the room calibration and setup sticky thread at the top of this forum, and have your properly level/eq calibrated speakers as per standards.

As far as Dolby SR, or Dolby Surround, search this forum for "Pro Logic" and/or "steering chip" (including the quotation marks) and you'll find some good reading about the matrix encode/decode that is part of Dolby SR. It is not like listening to discrete channels! If you are mixing with only two speakers you cannot judge the panning at all and may be in for quite a shock when you hear your mix played through a Dolby SR 4.0 surround system.

[minister]

i was confused by this at first too. if i remember the research right, in the mid-80's, Dolby introduced Dolby SR (which stands for Spectral Recording) that provided more noise reduction than conventional Dolby A. it improved optical tracks in general. the SR treated 35MM films even play in non-SR equipped theaters. analog soundtracks, i think, are virtually all Dolby SR tracks.

when Dolby introduced Dolby Digital, in the early 90's, they put a six-channel digital optical soundtrack on 35 mm prints so, they needed a four-channel SR (SuRround) analog track-aka LCRS. The SR analog track will play any cinema not equipped for Dolby Digital.

don't know why they made it confusing, but maybe Spectra Recording was good and so was SuRround • Digital. maybe someone else knows that.