Film-Tech Forum ARCHIVE: Analog sound distorced

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Posted by Antonio Marcheselli (Member # 373) on 04-25-2001, 05:46 PM:

Hello everyone.

I have a problem with one of my Cinemeccanica V5. I have reverse scan analog soundhead and Analog sound appears distorced when played but not always and not with all prints.
Let's me explain from the beginning.
Once I was in the auditorium and I heard some "foreign" sounds from surrounds. Like sound was croaking.
Next day I've performed Dolby level on both projectors and I found that on that projector the level wasn't stable. Once calibrated (in manual) after few seconds it went out of calibration again.
So I have our tech to check our A-chain EQ and all seemed to be right after that.
Unfortunately this problem seems to be intermittent and today I've heard "Atlantis" trailer in SR instead of DD. Audio completely distorced, particularly surrounds.
Perhaps I'm wrong but it seems like some "buzz" were behind surrounds sound but not continuing.
Do you have some ideas?

What about led power supply?

Bye
Antonio

Posted by Greg Mueller (Member # 17) on 04-25-2001, 06:03 PM:

That happened to me once. It turned out that the reader was misaligned and reading part of the DTS track.

By the way Brad, I like the new smiley face legend

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

Posted by Antonio Marcheselli (Member # 373) on 04-25-2001, 06:17 PM:

Greg,

If my reader is reading part of DTS or perforation, I should hear thumping, bumping or similar sound always, right?

Antonio

Posted by Greg Mueller (Member # 17) on 04-25-2001, 07:31 PM:

Well, I don't know for sure. But with mine the analog just sounded weak and distorted and crackly. The thump and bump would not always be there. Can you check it with some buzz track and a scope?

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

Posted by Aaron Sisemore (Member # 145) on 04-25-2001, 08:12 PM:

>>If my reader is reading part of DTS or perforation, I should hear thumping, bumping or similar sound always, right?<<

If the DTS timecode is being picked up at the solar cell, it will sound like a grinding, rumbling, or as you described, 'croaking' usually rhymically (like a 'wocka-wocka-wocka' or 'modem noise' type sound, usually heavy in the bass region unless the timecode is really in the scanning beam) usually in one or more channels (uaually the loudest in the left channel if played in stereo).

Perforations being read will cause a constant 96Hz 'humming' or 'buzzing' tone, also varying in volume and timbre depending on how much of the perfs are being read by the beam.

Either way something is not holding your film in alignment as its running, however there are instances of prints with the DTS code printed too far to the right making it impossible to avoid reading timecode, usually necessitating a replacement reel.

Hope This Helps!

Aaron

Posted by John Walsh (Member # 168) on 04-25-2001, 10:30 PM:

I would agree with everyone, but would like to add a comment. With design of the Cinemecannica V- series soundhead, it is very easily knocked out of alignment.

If it happens at random times, I would not think there's anything wrong with the power supply (at least, not at first.)

We also have some projectors with DTS "buzz." Totally random when it will occur- some reels will do it, others won't.

Posted by Paul G. Thompson (Member # 655) on 04-26-2001, 02:00 AM:

Sounds like an alignment problem. Frame line clip will sound like a motorboat idling, and as Aaron pointed out, perf clipping is 96hz buzz.

Posted by John Pytlak (Member # 331) on 04-26-2001, 07:45 AM:

Any chance Film-Tech could have a library of audio files on-line, so people could hear what various problems sound like? (e.g., 96 perf "motorboating", scanning the DTS time code, poor soundtrack application "whooshing" and "thumping", sibilant distortion, clipping, wow/flutter, etc.).

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Brad Miller (Member # 2) on 04-26-2001, 11:02 AM:

Actually I was discussing that very thing with Joe just last night over this discussion. It won't be on the near horizon, but it will be somewhere on the horizon.

Posted by Aaron Sisemore (Member # 145) on 04-26-2001, 11:50 AM:

Great idea, John! I'll get right to recording some examples!

Aaron

Posted by Antonio Marcheselli (Member # 373) on 04-26-2001, 05:19 PM:

Thanks to everyone!

I cannot understand very well the problem. First of all "atlantis" trailer has no DTS timecode (Unfortunately in Italy we don't have DTS encoded trailers...). Yes, on bass frequencies distortions were more audible.
With "not always" I mean this:

I started with "Recess, school out" trailer (before "Emperor's new groove" movie). The distortions were hardly audible.
As soon as "Atlantis" has started, distortions became immediately audible, particulary on surrounds.
While surrounds were distorcing, it seemed to me like some "buzz" or foreign sounds came into surrounds sound.
After that trailer I have local publicity (how do you call it? Policy?) in SR. Yes, sound quality is not the best but I have no distorced sound on it.
I will try to hear the movie in SR sound.
I remember when I had "American Psyco" trailer: last trailer on Proj 2 had bad DD so first 30 seconds of First trailer on Proj (American Psyco) were in SR (Cp500 waited few seconds before "trust" in new data!): completely distorced (voice and music, particulary low frequencies): at that time I thought that was just a badly recorded trailer...

Antonio

Posted by Mark Gulbrandsen (Member # 72) on 04-26-2001, 08:04 PM:

When I have heard the DTS track being scanned it best resembles the sound of a Pratt & Whitney 10 cylinder radial airplane engine. Just don't get in its way, but remember to put a bucket under the exhausts to catch that inevitable oil dripping while its idle!
Mark @ GTS