This is topic Need for delay in surrounds with digital? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Frank Angel (Member # 248) on 02-22-2002, 06:16 AM:
Dolby analog surround is delayed so that the bleed, especially of dialogue from the front channels is "masked" by the audio illusion of no sound being there if it arrives at your ear slightly later than the front sound (your ear being the spot the tech was standing when he aligned the system -- everywhere else it sucks). The only sound (in theory) that you will hear when the surrounds are delayed properly will be that which is not present in the front channels. But what happens with digital -- or even mag for that matter, where the surround channel are descrete? Logic would dictate that there would then be no need for the delay, except for really large theatres where you need delay just so that the surround audio doesn't arrive at the ear significantly later than the front sound, otherwise you wind up with an echo. I have Eventide delays for the two surround channels with two outputs, one for the orchestra and one for the balcony. Both are set first to make the surround sound arrive at the same time as the front sound, in each of the two distances. Then when aligning the CP50, the Eventides are used to increase the delay for the needed additional lag value from the arrival time of the front channels (as per standard Dolby setup). In this setup the CP is not used to set the delay. So, With DTS, do the settings for the surrounds have to be changed so the delay units DON'T add lag between the front and rear, i.e., the surrounds should be timed so that sounds from the rear arrive at the same time as the front sounds at the mean test point?
Does DTS, Dolby (re: SRD) and/or Sony discuss the need (or not) for delay in the surround channels?
Hmmm, this doesn't sound like I am explaining it clearly. Anyone understand what I am talking about?
Posted by Greg Mueller (Member # 17) on 02-22-2002, 09:42 AM:
In my screeniing room (tiny) I set the delay on "1" and it seems to give it a more spacious sound and I like it a lot more. Just thought I'd throw that in.------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
Posted by Ian Price (Member # 14) on 02-22-2002, 02:03 PM:
I asked this question of Lonny Jennings when he installed our first Dolby Digital unit at the Greenwood in 1992 or 1993. His response was that no, delay wasn't needed in digital systems but in the interest of keeping things working the same way going through the processor that delay was factored in to the digital sound so that it sounded normal when the surrounds were delayed in the CP65. This also alowed the B-chain to remain the same for Analoque and Digital sound in regards to room size.
Posted by Gordon McLeod (Member # 33) on 02-22-2002, 03:39 PM:
The Haas effect still is there even in digital that although cross talk is not an issue the same information could be recorded in a screen and a surround channel producing an echo.
So there is a delay adjustment
MAG and DTS actually have a offset built in that dates back to fox'w specs back in the 50's for cinemascope and I can't remember what it is
Posted by Frank Angel (Member # 248) on 02-23-2002, 05:08 PM:
Makes sense. I think with surround delay, your ears are the best judge. Whatever is right for the analog, I'll just leave for the DTS. If I hear echo, I can always back it off with the Eventides. The balcony was the big question because that has much longer delay, in addition to the CP.
Posted by John Wilson (Member # 269) on 02-23-2002, 09:00 PM:
GordonYou mean the DTS itself has a delay or relies on the delay of the CP-whatever.
John
Posted by Gordon McLeod (Member # 33) on 02-23-2002, 09:05 PM:
DTS and Mag have the delay recorded into them as a fixed amount somehow 1.5 frames rings a bell
Posted by Karen Hultgren (Member # 395) on 02-25-2002, 11:51 AM:
When we transfer the soundtrack into DTS, we put in surround delay (so, it's already done on the discs).Karen at DTS
Posted by Ray Derrick (Member # 1001) on 02-26-2002, 03:36 AM:
In theory, Digital requires 10 to 20mS less surround delay than optical but as has already been pointed out, the centre-to-surround crosstalk is not an issue, so the setting is not as critical as it is for optical.The DA20 has adjustable digital surround delay and the setup procedure is described on page 4.3 of the installation manual. With CP500 and 650 there are separate adjustments for optical and digital surround delay although the 650 can automatically calculate the digital delay from the analog setting.
DTS has an in-built fixed delay of 50mS (which as Karen has stated is on the discs, not in the player). If you have a big theatre and need more, then with most analog processors you have to add it externally.
SDDS DFP-D3000 uses the same setting for both optical and digital surround delay.
------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935