Film-Tech Forum ARCHIVE: Sound problem with DTS film

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Posted by David Rigby (Member # 1301) on 06-16-2003, 04:24 PM:

When I played a film with a DTS track the other night on my Vic 4 I found that there was an intermittent low pitched noise in the left channel - almost like white noise but less shrill. My assumption is that the Dolby cell is slightly out of alignment and so the left channel is picking up some of the timecode. is this correct or should I be looking elsewhere? The solar cell alignment was only done pretty coarsely when the cell was installed since I didn't have my CP50 working at the time.

David

Posted by Brad Miller (Member # 2) on 06-16-2003, 04:40 PM:

Try gently pressing the film inward a hair while it is running and see if the noise goes away.

Do you by any chance have a buzz track loop of film?

Posted by John Pytlak (Member # 331) on 06-16-2003, 04:54 PM:

Assuming you were playing the analog track, I agree with Brad that you should check the lateral alignment. Sometimes the edge of the silver application is close to the edge of the scanned area, and could result in a noise like you describe. Accidently scanning the DTS track would be an irregular square-wave "putt-putt" or "motorboat" noise, and not a hissy "white noise".

Posted by Bruce Hansen (Member # 281) on 06-16-2003, 05:10 PM:

If you run a film without DTS time code, do you still get the same noise?

Posted by David Rigby (Member # 1301) on 06-17-2003, 03:56 AM:

The noise only appears on DTS film. I've never heard it on a plain old analogue track. Interestingly, it didn't happen on every reel of the DTS print, but on about 5 of 7 - and sometimes it vanishes for extended periods (say 10 minutes) in a reel. I'll try the nudging trick to see if it goes away. The fact that the noise was only in the left channel is what made me think it's the DTS track.
(NB I'm currently only using the preamp output on my CP50, so only 2 channels).

John - the description as 'white noise' was probably not a good one on my part : it's fairly low pitched but has a similar 'random' quality to white noise. Perhaps it could be described as a 'motor boat' noise. Not sure if I have a buzz track - I may well have a loop sitting around somewhere; I'll take a look.

Thanks guys

David

Posted by Michael Schaffer (Member # 1204) on 06-17-2003, 04:12 AM:

It happens from time to time. I remember the German prints of "Titanic" had misprinted timecode on some reels. So some smaller second-run theatres with analog only couldn`t play the film without severe sound problems.

Posted by David Rigby (Member # 1301) on 06-17-2003, 07:34 AM:

Hmm. I did wonder whether it might be a printing problem since the background noise isn't there 100% of the time. I'd prefer a cell misalignment since that's just a bit of fiddling. I'll post here with what I find over the weekend (probably won't get time to sort this before then).

For future reference, how common are timecode printing problems?

Thanks as always folks

David

Posted by Mitchell Dvoskin (Member # 751) on 06-17-2003, 07:40 AM:

The only way you are going to know is with an official buzz track loop. Adjusting by ear with release prints will drive you crazy, since many of them are printed slightly out of spec.

Posted by John Pytlak (Member # 331) on 06-17-2003, 08:10 AM:

SMPTE Recommended Practice RP115 specifies the position of the Photographic Control and Data Record on 35mm prints. The centerline should be 0.297 inches (7.54mm) from the reference edge of the print. The inner edge of the analog audio record should be 0.281 inches (7.14mm) from the reference edge.

Posted by Gordon McLeod (Member # 33) on 06-18-2003, 09:18 PM:

remeber that the cinemecanica slits have a width adjustment so once the lens assembly is correctly centred its width is adjusted to limit its scanning width to between the two tones of the smpte buzz track

Posted by Rick Long (Member # 213) on 06-18-2003, 11:44 PM:

Perhaps the best description of DTS being picked up in the optical scanner is "kinda sounds like a vaccum cleaner".

Posted by Mark Gulbrandsen (Member # 72) on 06-19-2003, 09:02 AM:

"Perhaps the best description of DTS being picked up in the optical scanner is "kinda sounds like a vaccum cleaner"."
_________________________________________________________________
On a system with good subwoofers it also can sound like a A Pratt And Whitney radial airplane engine...... The only thing you're missing is the 100 mph hurricane force winds that are also being generated by the propeller..... [Eek!]

Posted by Randy Stankey (Member # 64) on 06-19-2003, 10:30 AM:

When I had reports of alignment problems that caused the DTS track to be read in the analog reader I would ask the person if it sounded like a computer modem.

Posted by Larry Zuverink (Member # 1483) on 06-19-2003, 01:44 PM:

V4's as well as V9's are known for having very week cells. Any little thing can knock them out of alignment. Even worse with the Kelmar cell. So even if it had been aligned at first it could be a mile and a half off now. Your best bet is a full A-chain.

Posted by Karen Hultgren (Member # 395) on 06-19-2003, 04:58 PM:

Use a buzz track loop and realign your solar cell - it's picking up the DTS track.

Karen at DTS
khultgren@dtsonline.com

Posted by Paul G. Thompson (Member # 655) on 06-19-2003, 08:35 PM:

I agree.

This has been a pain in the butt for me, too. I have a 5-Star sound head, and I know what the problem is. However, I have not yet found the time to correct the problem. I have to practically dismantle the sound head to fix it.

The noise mine makes when it scans the DTS track can be compared to the noise the particle gun makes in the "Martian Chronicles."