Film-Tech Forum ARCHIVE: AB-Chain

This is topic AB-Chain in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Ram Sup (Member # 4711) on 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.

Posted by Scott Norwood (Member # 30) on 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.

Posted by Darryl Spicer (Member # 711) on 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.

Posted by Sean McKinnon (Member # 612) on 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.

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Louis Bornwasser (Member # 3063) on 03-20-2008, 07:52 PM:

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

Posted by System Notices (Member # 2357) on 09-23-2010, 01:48 PM:

It has been 916 days since the last post.

Posted by Todd Cornwall (Member # 2205) on 09-23-2010, 01:48 PM:

What would good reference material be?

Posted by Gordon McLeod (Member # 33) on 09-23-2010, 03:32 PM:

The Dolby CP200 manual is a good reference

Posted by Marco Giustini (Member # 4544) on 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.

Posted by Todd Cornwall (Member # 2205) on 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.

Posted by Frank Angel (Member # 248) on 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?

Posted by Gordon McLeod (Member # 33) on 09-24-2010, 10:34 AM:

Dolby Jiffy and I still like Dolby Listen

Posted by Randy Stankey (Member # 64) on 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]

Posted by Gordon McLeod (Member # 33) on 09-24-2010, 11:47 AM:

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

Posted by Manny Knowles (Member # 1171) on 09-24-2010, 12:31 PM:

Yeah, but...if it was playing off a disc it wouldn't be a test of the analog A-chain.

As for dub stage experience - I've been lucky enough to have heard print masters of the original Star Wars, Raiders of the Lost Ark, Terminator 2, The Translator and others - on dub stages.

For a long time I used the original R-5 of Bug's Life...the reel that was replaced with new out-takes and then never got collected from my theatre. And then, one day I had to let that reel go.

I used to help Tom Holman calibrate the dub stages at USC and he uses a variety of media and recording types. Dialog only - male only and female only. These were a test for level and intelligibility (reflections).

As an actual scene, a favorite was R-1 of Master and Commander because he had actually heard it on a dub stage and then the re-recording mixer heard it in our main theatre. It is a good reel with lots of detail and dynamic range.

And then, of course, music. One of the Dolby reels had a piano recording that would really show if you had any wow/flutter. It wasn't on the Jiffy Test -- but could it be the Listen reel?

R-1 of Pure Country is also amazing for showing off dynamic range. Wow!

Posted by Tony Bandiera Jr (Member # 2365) on 09-24-2010, 12:46 PM:

Manny, I think it is the "Listen" reel if you are talking about a full song on piano, but on the "Jiffy" reel there is a single piano chord used to check for wow and flutter...plus that goofy electronic music section by Wendy Carlos at the end of the reel. [Big Grin]

You are right that reel 1 of Pure Country is a great test reel..one of Dolby's techs had that reel and used it check out some installs I had done.

Posted by Manny Knowles (Member # 1171) on 09-24-2010, 01:20 PM:

Oh, that was Wendy Carlos... [puke]

Posted by Sean McKinnon (Member # 612) on 09-24-2010, 02:11 PM:

quote:
This is catalog number two five one S R D

quote: Manny Knowles
As an actual scene, a favorite was R-1 of Master and Commander because he had actually heard it on a dub stage and then the re-recording mixer heard it in our main theatre. It is a good reel with lots of detail and dynamic range

I got to hear this reel played at the dolby screening room in San Francisco. It was super cool!

quote: Tony Bandiera Jr
plus that goofy electronic music section by Wendy Carlos at the end of the reel.

I love that "goofy" music part!

Posted by Todd Cornwall (Member # 2205) on 09-24-2010, 07:53 PM:

I've got a lot of brushing up to do I guess

Posted by Manny Knowles (Member # 1171) on 09-25-2010, 04:40 PM:

I wonder if you could clarify what you mean? Are you having a particular problem? Maybe we can help?

Posted by Todd Cornwall (Member # 2205) on 09-25-2010, 06:56 PM:

Not a particular problem, no. I was just looking into A-B chain alignments and checking for some good reference material to have.