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» Film-Tech Forum   » Operations   » Digital Cinema Forum   » What to use for room EQ?

   
Author Topic: What to use for room EQ?
Phil Ranucci
Expert Film Handler

Posts: 227
From: Carpinteria,CA, United States
Registered: May 2006


 - posted 06-28-2013 11:53 PM      Profile for Phil Ranucci   Email Phil Ranucci   Send New Private Message       Edit/Delete Post 
I put this in the digital forum because it'll probably get more views.
What's out there for doing room EQ?
I've seen these 2:

Acoust-X D2 which is a complete system, ready to use.

USL multiplexer and an RTA. Is there any way to use this system with a laptop running SMAART? That way the RTA can stay home.

Does Dolby even make their system anymore? Did they ever sell it?

Any others I don't know about?

I'm looking for pros/cons of these systems and would appreciate any insight as to the best path.
Thanks!

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Harold Hallikainen
Jedi Master Film Handler

Posts: 721
From: Denver, CO, USA
Registered: Aug 2009


 - posted 06-29-2013 12:01 AM      Profile for Harold Hallikainen   Author's Homepage   Email Harold Hallikainen   Send New Private Message       Edit/Delete Post 
Hi Phil!

OF course, the USL MMP can drive the RTA within the processor. The Dolby CP-750, USL JSD-60, and JSD-100 also include an auto-eq that should get you close. You can then fine tune.

SMPTE is doing a complete review of cinema sound systems, including various eq techniques, pink noise sources, etc.

Harold

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12083
From: Annapolis, MD
Registered: Dec 1999


 - posted 06-29-2013 10:59 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
What makes the D2 rise to the top of the list is that it is fully calibrated in both frequency and level. It also self-normalizes.

What that means is that one need not calibrate each mic level to normalize it to 85dBc. Mic 1 is the reference and should be located as per SMPTE 202.

If you use a D2 (or an R2) and someone else uses one to check the same room, they will see the same response (within a dB or so for the entire frequency range)...no other system can really claim that. There is a consistency and uniformity to it.

In the USL system (note USL makes the plexer in the D2 system), it is up to YOU to calibrate EACH mic on EACH tuning to get the levels balanced. If you don't calibrate them, then the mic nearest the stage speakers will have more influence over the tuning than the far one. Thus you cease to get an average tuning and are drifting more towards tuning for one seat. There is also but so much USL can do to "calibrate" the mics (or any other non-DSP based plexer)...in a DSP based system like the D2, each mic has an offset file that has it measure exactly flat.

You also have to get the rate of change on a wild plexer such that your analyzer will actually do the averaging correctly.

Now some of the newer stuff coming out, like Dolby Atmos is using DSP to locate each speaker relative to the mic(s) and will thus do accurate autotuning...one just has to have very flat microphones so that the mic does not color the measured results.

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Dave Macaulay
Film God

Posts: 2079
From: Toronto, Canada
Registered: Apr 2001


 - posted 06-29-2013 11:27 AM      Profile for Dave Macaulay   Email Dave Macaulay   Send New Private Message       Edit/Delete Post 
There is, I suppose, an "ideal" tuning method. In my reality I have to do as good a job as I can with limited time and a limited equipment budget: probably most techs are in the same situation.
I use the R2 sometimes, but usually a USL plexer and (for older processors) Smaart. I'm not convinced the R2 does a better job than the built in RTA functions on modern processors, and moving it is a hassle. I think it is better than Smaart but, again, carrying the R2 is a hassle.
I use an outboard USB sound card with Smaart, I wouldn't trust a laptop's internal A-D. Possibly an outboard RTA would be better than Smaart but I haven't found an affordable one with anywhere close to the capabilities of Smaart.
Final channel levels get set with a portable SPL meter.
I have set the USL mic level matching myself, but they have always been pretty closely matched from USL. I adjust the output level to be a good level on a new CP750 without adjusting the CP750 mic input level trim.
I can't imagine what Steve means by calibrating "EACH mic on EACH tuning". Or what it would accomplish: each mic is a different distance from each speaker, so what would they be calibrated to?
I do use "EQ Assist" when available, it gives a decent starting point. It is not perfect. Smoothing out extreme band offsets is usually required, and actual listening and tweaking is advisable.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12083
From: Annapolis, MD
Registered: Dec 1999


 - posted 06-29-2013 12:02 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Lets say your Mic-1 is reading 85dBC and is in the typical single-mic location as identified in SMPTE 202. So, presuming you are still following 202 and are using a form of the "staggered diamond" formation, the mic closest to the speakers is going to read higher than mic 1...the reference location. In a longish room it could be several dB higher due to the inverse square law on how sound levels drop over distance. The mic closer to the screen is going to have a GREATER influence over the response than Mic 1 since it is going to read lower.

If you calibrate your mics so that if Mic 1 reads 85dBC, that all of the other mics ALSO read 85dBC (really you want the average of all of the bands to be the same level as mic 1) you will eliminate the emphasis of one particular location and get a true average level. It is a reason that the R2/D2 will always get a uniform response regardless of who did the work.

I agree that the R2 is a bit of a pain due to its size/weight. The D2 is really no bigger than the USL rig if you are using an outboard mic preamp. That is what I carry on all of our set ups now.

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Marco Giustini
Film God

Posts: 2536
From: Reading, UK
Registered: Nov 2007


 - posted 06-29-2013 02:07 PM      Profile for Marco Giustini   Email Marco Giustini   Send New Private Message       Edit/Delete Post 
I have never got much luck with external sound cards or D/A - no matter how good they were. I don't know why but they read too little HF compared to a D2, even with the entire system (mike + A/D) calibrated in frequency.

IMHO one of the key elements of a good EQ is not to use a single position. Whether you use a multiplexer or a single mike averaged in several positions (these days WiFi is helping a lot!) it's crucial not to just tape a mike to a broom and dial the X-Curve.

And as Dave points out this has to be done in a limited amount of time with lots of restrictions in place - i.e. poor speakers/amps, poor acoustics...

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