Film-Tech Forum ARCHIVE: SR.D HD

This is topic SR.D HD in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=008526

Posted by Gunnar Johansson (Member # 1661) on 02-24-2007, 10:42 AM:

Me and some colleagues have lately been noticing prints coming with SR.D HD written on the head. No search on google or on the Dolby website gave any useful information.

-Is it in High Definition? Then why no upgrades to the readers?
-Is it from the Hard Drive, meaning it's digital all the way and never was analogue (everything made on synthesizers?)
-Is it arriving on a Harley Davidson and not by bus or train as the rest of the prints?

I tried searching the forum as well but it didn't seem like it had been discussed. I hope someone can help us, we're dying to know.

Posted by Christian Appelt (Member # 1067) on 02-24-2007, 11:49 AM:

Maybe they were to lazy to write HEAD (of sound negative reel)? [Smile]

Posted by Mike Olpin (Member # 1115) on 02-24-2007, 01:11 PM:

Perhaps Dolby is trying to differentiate between the higher bandwidth data streams used in cinemas and the lower bit streams used on DVD. In the home market, Dolby is also pushing a new higher bandwidth audio format called Dolby TrueHD .

Related?

Posted by Bobby Henderson (Member # 840) on 02-24-2007, 02:15 PM:

The "HD" thing is probably just a bunch of bullcrap, just like the "HD" term in "HD Digital Radio."

There would have to be some significant physical change in the data bitmap Dolby Digital has printed between the sprocket holes to come up with any big improvement on the system. The standard bitmap yields a maximum of roughly 550,000 bits per second, but only 320,000 bits are used for the primary soundtrack. The rest is used for error correction. I could see some tweaking being done to raise the main audio bitrate to 384kb/s or 448kb/s to match what is on standard DVDs. However, a lot less data would be left for the error correction function and risk harming system reliability.

Dolby TrueHD is something entirely different from the standard Dolby Digital format used in movie theaters. It operates at much higher bitrates and bit word lengths. It can do 24-bit 96kHz audio in lossless compressed form and do so across 8 or more channels. It can feature bitrates in excess of 6Mb/s.

Dolby Digital Plus operates at lower bitrates than Dolby TrueHD, but its data load is well above the 640kb/s maximum allowed by standard Dolby Digital decoders.

FWIW, DTS' new DTS-HD formats aren't getting used in commercial movie theaters either. DTS-HD High Res and DTS-HD Master are similar in function to Dolby TrueHD, but can be ballooned out to huge bitrates, up to 24.5 million bits per second played from Blu-Ray discs across HDMI 1.3 digital connections. 24-bit 192kHz audio is possible.

With use of a dual-system approach, any of that kind of audio is possible with a 35mm or 70mm film presentation. But there simply isn't any way anyone is going to print that kind of digital data on a 35mm film strip and get reliable playback from microscopic data spot sizes.

Posted by Chris Trainor (Member # 9) on 02-27-2007, 02:49 PM:

Actually Mike, the data rate on film is a bit lower then on DVD (320kbps or so vs 384kbps default on DVD). Plus, DVD has room to expand, unfortunately unless they add a set of blocks on the other side of the film they're kinda stuck with the film based datarates for SR-D. [Frown]

Tho also keep in mind the DVD rate can be variable... you could in theory author it lower or higher as needed. The ATSC rate I think is also 384kbps (for Over The Air HDTV)

--Chris

Posted by Bobby Henderson (Member # 840) on 02-27-2007, 03:46 PM:

Standard Dolby Digital, be it on disc or a 35mm film print, has a maximum bitrate of 640kb/s. Some technical issues with DVD confine the DD bitrate there to a maximum of 448kb/s. Some HD-DVD and Blu-Ray discs feature standard DD tracks with 640kb/s bitrates.

Dolby Digital Plus is an elaboration upon Dolby Digital. It has a core data set that is backward compatible with existing Dolby Digital decoders. It has additional data above the 640kb/s limit to improve audio resolution, bit word length, sample rate and more. HD-DVD and Blu-Ray players can internally decode the data and export via analog output or if you have a HDMI-equipped receiver with DD-Plus capable decoding the job can be done there.

Dolby TrueHD is, at least from my understanding, a completely new format and not backward compatible with standard Dolby Digital decoders.