Film-Tech Forum ARCHIVE: DTS/SRD mix differences

This is topic DTS/SRD mix differences in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jack Ondracek (Member # 1466) on 03-19-2004, 11:30 PM:

This is a content question... not one of quality comparison:

Some time ago, I think I read here that there should be little, if any difference between one system and another, given a particular soundtrack.

I've noticed here that the surrounds kick in much less often with my DA20(/CP65) than with my DTS(/CP65) houses.

I haven't taken the time to check anything specific... like when I move a print from a DTS screen to the Dolby house. However, there are times when there's plenty of surround on the SR track... mainly ambient background stuff... switching to SRD kills it (yes, the SR is aligned), so it is noticeable in that respect.

Just curious... I was under the impression they should all be the same.

Posted by Richard Fowler (Member # 893) on 03-20-2004, 02:19 AM:

Each digital process has to be encoded through their equipment in order to make the track. The original master stems, assuming they have more than enough information, can give different end results due to the different compression schemes used by DTS/DOLBY/SDDS. I have noticed the difference in some films playing in cinemas that we set up which where equipped for the three formats.......but the paying audience could not judge due to a lack of opportunity to compare.....at least you are aware [Wink]

Posted by Brad Miller (Member # 2) on 03-20-2004, 06:12 AM:

quote:
I've noticed here that the surrounds kick in much less often with my DA20(/CP65) than with my DTS(/CP65) houses.

That's the problem. A DA20 into a CP65 pads down the digital surround level by 3db. I think Dolby has a fix for that, but the few CP65s I have running are just set 3db hotter. It never defaults to analog anyway.

Posted by Jack Ondracek (Member # 1466) on 03-20-2004, 08:27 PM:

Thanks! That's what I was looking for.

Posted by Alan Haigh (Member # 1781) on 03-22-2004, 04:29 AM:

Remember the SR track will have more on the surrounds anyway. This is generated from the front channels (anything equal and in phase goes to the surrounds). So under normal conditions you will hear more on the surrounds in SR.

The 3dB thing shouldn't make a difference. SRD has 2 channels for surround and SR only has one, so you need to decrease the SRD signals by 3dB to make them match. It's all accounted for in the studio - surrounds are set to 82dB at reference level. This is the same in all formats - so I would check that you have 300mV at all outputs on the DTS unit when playing 1kHz from the DS3 or DS5 test disks (don't use the DS1!).

Posted by Christos Mitsakis (Member # 143) on 03-22-2004, 10:47 AM:

Alan you mistyped. Anything equal and IN phase in Lt and Rt goes to the centre channel and anything equal and OUT of phase goes to the surround channel.

The digital surrounds are set to 82dB so when there is a mono signal it produces 85dB at reference level.

Brad is very right. CP65 pads down the surrounds by 3dB. Digital calibration requires Ls and Rs to be set at 85dB (instead of 82) and a mono signal produces 88dB at reference level. Someone mentioned that this is a peculiarity of the Cat. 441 card. If this is so does anyone knows why?

Christos.

Posted by Alan Haigh (Member # 1781) on 03-25-2004, 07:33 AM:

Thanks for correcting me Cristos. I still find it all bizarre though, I can see a reason to pad down the surrounds from the SRD, because of headroom in the CP65, but why not reduce the S channel from the matrix as well. It would just be one resistor on that card and would all be fine. Are you sure that it's not like this anyway? -the only way to test it would be with surround only pink noise on film, or the pink noise sweep round test on the Jiffy film - does this really get 3dB louder at the back?

Posted by Gordon McLeod (Member # 33) on 03-25-2004, 09:33 AM:

I think the3db came about from the old choocho surruound test film that often due to errors in the matrix ended up with the optical surrounds sitting at 88db compared to the mag surround (cp200 ad the seperate optical surround level adjustment)

Posted by Christos Mitsakis (Member # 143) on 03-26-2004, 12:25 PM:

Gordon, If it were early matrix design fault, then the same procedure of alignement should apply to CP55 and older processors. Even when using cat 241 for surround eq the final level is set at 85dB at ref level. When you upgrade CP55 for digital with cat. 441, the same level adjustment for CP65 is used. So something is inherent with the 441 card.

Posted by Gordon McLeod (Member # 33) on 03-26-2004, 05:58 PM:

With all processors the optical surround level is set with the cat 151 cho choo test film

Posted by Steve Guttag (Member # 268) on 03-26-2004, 06:39 PM:

In truth...it isn't that the CP-65 pads down the Digital surrounds it is that it boosts optical surround by 3dB. The origin comes, as Gordon states, from earlier processors that if one set the surrounds to 85dB and then ran Cat. 151 test film, more often than not, people would set the surrounds by ear such that they were 3dB louder. The Cat. 441 just made this automatic.

If you don't like this feature, the removal of resistor R127 (28.7K 1%) will eliminate the 3dB boost and the optical, magnetic and digital surround levels will all be identical. Only Non-Sync surround will be potentially greater using the Non-Sync surround trim.

Next.

Steve

Posted by Christos Mitsakis (Member # 143) on 03-27-2004, 09:46 AM:

Steve,
Thanks for the clarification.
Gordon,
When I use Cat 151 test film, I always measure with a SPL meter the average surround array level than setting it subjectively. It's not that I don't trust my ears but I prefer things to be exact. (Only in Equing I trust my ears for final tuning).
Regards,
Christos