Film-Tech Forum ARCHIVE: DTS Timecode on Riddick causing sound probs

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Posted by Matthew Nock (Member # 1575) on 07-29-2004, 09:36 AM:

Hi All,

hoping that all the intelligence here on Film-Tech will confirm my suspicions regarding a strange sound problem we have encountered today when showing Riddick on our DTS house.

The print was originally screened in our largest house (Century DA proj, with DA20 and a 701? basement reader). Both Optical and Digital worked a-okay.

However, we moved it to our slightly smaller house this evening, and wouldnt you know it, we didnt receive the DTS disks so we ran the show in optical. No big deal, our optical sounds great (just a little less dynamic that DTS or Digital).

However, from about 1/2 way through reel 2 onwards (well, for every reel that I checked after the customer complained), we noticed a noise similar to what is described as motorboating in other threads.

I went through all the usual checks - made sure film was sitting snugly around the sound drum, that the tension rollers around the sound head were firm etc, gave a great blow of air across the sound head. However, the noise persisted on the soundtrack.

The noise only occured in the left channel (which leads me to beleive its the DTS track printed slightly close). Centre, Right and Surrounds seem un-affected. The problem is both at the processor output, as well as in the auditorium. We ran I, Robot in that theatre following the session of Riddick (no -problem, except that we turned the DTS player off to confirm it wasnt an optical alignment prob).

The projector is a Century DA, with what looks like a standard Century Sound head, but it appears to have been fitted with Kelmar LED reader assy.

Would i be correct in thinking that maybe the LED reader in this machine is just out but a tiny bit, and the fact that the DTS track on this print just comes a little too close, that that is why we are getting this sound?

Any thoughts, suggestions? We are a regional cinema, and I dont fancy having to pay for a tech to travel over 250km to get here to do a 10 minute job.

Thanks,

M@

Posted by John Pytlak (Member # 331) on 07-29-2004, 10:00 AM:

Yes, you MAY have an alignment problem in the analog reader. But do check the position of the DTS and analog track on the print to be sure is is not a problem reel(s). The centerline of the DTS should be 7.54 +/- 0.03 millimeters from the reference edge of the print (SMPTE RP115), and the centerline of the analog track should be 6.17 +/- 0.03 millimeters from the edge of the film.

Posted by Matthew Nock (Member # 1575) on 07-29-2004, 10:07 AM:

Hi John,

Thanks for your reply - I will check the actual print itself tomorrow. The main thing that makes me wonder whether it was the actual print as opposed to the analog reader alignment is the fact that no other print is exhibiting this problem... only this print of riddick. maybe its just because its a really bad movie! [Smile]

I will measure tomorrow morning and see how it pans out...

Posted by Steve Guttag (Member # 268) on 07-30-2004, 08:12 PM:

Don't rule out that it may be the sum of two problems...the DTS timecode printed a little off towards the soundtrack...and your optical sound reader's lateral position may be a little off. If you have SMPTE's "Buzz-track" (P35-BT) that will check out your sound reader without other test gear. My suspision is that you will hear the low tone, indicating that your reader is scaning too far inboard.

On some older Century projectors, is was nearly impossible to get the sound lateral guide roller to go inboard far enough without filing down the upper arm. There are also adjustments on the piviot bearings that will allow the arm to move over far enough. However, I'd run some Buzz track first.

Steve