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Topic: AB-Chain

Ram Sup
Film Handler

Posts: 57
From: Malaysia
Registered: Mar 2008

posted 03-20-2008 08:48 AM

Please give me a detailed guide to do A and B-chain Sound Alignment.What are software to use and can i get the softwares free.Any advice and help is very much appreciated.TQ.

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 03-20-2008 09:27 AM

You need (at minimum) a buzz-track loop and a pink-noise loop (try to get an older Dolby cat. 69 on B&W stock) for a mono system. An RTA is also good to have; otherwise you need someone with good ears.

The mono procedure is basically this: clean optics, use buzz-track to set lateral guides, use pink noise to set focus and azimuth (try to peak high frequency). Dolby tone or pink noise can be used to match the signal level with two projectors. Most mono systems don't have any EQ adjustment except for the speaker crossover (labelled "HF Attenuation" on Altec N500s), which you can set with an RTA (or by ear) by running pink-noise film (after doing the A-chain) and using the tap that gives the proper room response (rolling off the high frequencies, as the Dolby manuals discuss).

The procedure for Dolby systems in in their manuals. The CP50 manual is a good starting point and can be downloaded from the manuals section.

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 03-20-2008 12:23 PM

quote: Scott Norwood
An RTA is also good to have; otherwise you need someone with good ears.

You need both.

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Sean McKinnon
Phenomenal Film Handler

Posts: 1712
From: Peabody Massachusetts
Registered: Sep 2000

posted 03-20-2008 04:10 PM

How I do an A-Chain

1. I CLEAN THE OPTICS!

2. I start with Dolby Tone Cat. 69T and verify that I am getting the most signal level I can get out of the analog reader. I use my oscilloscope to check my signal level.

3. Then I run buzz track P35-BT and use an oscilloscope to adjust my lateral alignment

4. Then I run the left/right crosstalk film and use an oscilloscope to adjust the solar cell if present.

5. Next, I run Pink Noise Cat. 69P and adjust the frequency response and focus of the reader with an RTA and Oscilloscope.

6. Then I run the Dolby Tone Cat. 69T and adjust the optical pre-amp for proper "Dolby Tone"

7. I start at #1 again and make sure nothing has changed.

8. I run some reference material to vefify that it sounds good in the auditorium.

How I do a B-Chain

1. I verify the A-Chain

2. I set the amplifiers as reccomended for that particular amp.

3. I use my Pink Noise Generator and adjust each output level on the processor for 85DBC on my SPL meter (Except the subwoofer)

4. I set out my RTA Mics in the auditorium and adjust the frequency response on each channel to the X-Curve or ISO2969

5. I set the subwoofer level using my RTA

6. I re-check each channel to verify 85DBC with my pink noise generator and SPL meter.

7. I RUN REFERENCE MATERIAL TO MAKE SURE IT SOUNDS GOOD IN THE AUDITORIUM.

That is a simplified overview, it can get very involved when you add crossovers and parametric eq's but that is the simple process. I think this is the kind of thing that needs to be taught to someone in person and is an art to be handed down. I posted this simple overview because you asked but I would seek out an experienced tech to teach you.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 03-20-2008 04:39 PM

quote: Sean McKinnon
I RUN REFERENCE MATERIAL TO MAKE SURE IT SOUNDS GOOD IN THE AUDITORIUM.

I love that line... [thumbsup]

! There are but a handful of folks here that actually know what a given refrence reel SHOULD sound like... having heard it on the re-recording stage or in the presence of the the re-recording team that made the mix in a capable theater.

Mark

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 03-20-2008 07:52 PM

Right! Usually they tune and then run for the car! Louis

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System Notices
Forum Watchdog / Soup Nazi

Posts: 215

Registered: Apr 2004

posted 09-23-2010 01:48 PM

It has been 916 days since the last post.

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Todd Cornwall
Film Handler

Posts: 91
From: Madison, WI
Registered: Feb 2004

posted 09-23-2010 01:48 PM

What would good reference material be?

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 09-23-2010 03:32 PM

The Dolby CP200 manual is a good reference

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Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007

posted 09-23-2010 04:41 PM

A reel you know how should sound. I have one I heard in the post-production mixing room and I have an idea on how it should sound.

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Todd Cornwall
Film Handler

Posts: 91
From: Madison, WI
Registered: Feb 2004

posted 09-23-2010 07:00 PM

I've used trailers in the past, which I know is probably a bad idea, but I didn't know what else to use.

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 09-23-2010 11:52 PM

quote: Mark Gulbrandsen
I love that line... ! There are but a handful of folks here that actually know what a given refrence reel SHOULD sound like... having heard it on the re-recording stage or in the presence of the the re-recording team that made the mix in a capable theater.

Exactly. It's like classical music recording engineers who rarely go to live concerts (I know a few of these). How do they know what a chanber music ensemble or an orchestra is supposed to sound like if they don't ever hear them live acoustically?

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 09-24-2010 10:34 AM

Dolby Jiffy and I still like Dolby Listen

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 09-24-2010 11:09 AM

A little tidbit of information for you:

Back in the 1940's, the BBC's radio engineers used to use the song, "Teddy Bear's Picknic" by the Henry Hall Orchestra as their reference recording:

http://en.wikipedia.org/wiki/Teddy_Bears%27_Picnic#Use_by_BBC_Radio_Engineers

quote:
Use by BBC Radio Engineers

The 1932 Henry Hall recording was used for more than 30 years by BBC audio engineers (up until the early 1960s) to test and calibrate audio equipment. It was possibly last played at the end of the final transmission from the old Regional transmitters at Washford in the early 1980s.[citation needed]

Its especially good recording quality and the large tonal range of the music made it ideal for checking the frequency response of audio equipment. BBC Engineering even had special vinyl pressings made to reduce any surface noise.

http://www.youtube.com/watch?v=dZANKFxrcKU

For quite a while, I've wanted to get a high quality copy of that song to use as reference. [Big Grin]

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 09-24-2010 11:47 AM

actually it would be nice if dolby issued both those films on DVD as a test disk

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