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This topic comprises 3 pages: 1 2 3
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Topic: Soundtrack Format
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Steve Kraus
Film God
Posts: 4094
From: Chicago, IL, USA
Registered: May 2000
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posted 06-08-2002 10:50 AM
Both processes are in effect multiple compandors working on different frequency bands. By compandor (compressor - expander) we mean that the sound level variations are compressed on encoding and then expanded again on playback. This keeps everything well above the murk. A simple one processes the entire signal at once which means a high level signal at one frequency will reduce the compression and signals at other frequencies may drop down into the noise. Dolby's invention was to work independently on 4 frequency bands (Type A) and do so in a way that the decoding very acccurately undoes the encoding.
SR does the same thing but more heavily, with more bands, and the frequency ranges can slide a bit as needed depending on the signal. In both cases we are talking about bringing low level signals UP and then putting them back down. Compatibility is going to vary with the material but to some degree playback where low level signals have been raised by SR encoding, then lowered but not all the way by playback in A will result in audio that is still slightly compressed. This can sometimes be an advantage if the listening environment has high background noise. Audio with very wide dynamic range may be hard to hear if the quiet passages are very quiet. This type of playback may leave them a bit louder.As for the specific example of trailers it may also be that trailers tend to be recorded at such high levels that only minimal NR action that is applied. A characteristic of both processes is that high level signals pass through unchanged. Of course, as we have said elsewhere the SR optical soundtrack is recorded at a lower average level than A (just as A is recorded at a lower level than a typical mono track) so as to trade off a bit of the improved noise level for more range--an extremely loud sound can be that much louder than average dialog level without clipping. So when playing an SR track, a lower level signal, in A-type which is expecting a higher level signal you're automatically reducing the volume a few dB which may be helpful on trailers as well.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 06-09-2002 01:43 AM
Joe, while one may have to guess, at first, which NR to use on a print in question...it shouldn't take very long to determine which is the correct one! Heck, "knock off" SR cards sound like crap when trying to play back SR too (including the Cat. 222 SR/A). Maybe the only knock-off card that tracks it right is Panastereo's...I haven't listened to it enough to give it a thumbs up or down yet but so far so good.Pay attention to the upper frequencies...how A and SR handles them is quite different. SR has an "spectral skewing" that will make it very bright if played back with A. Steve K already pointed out that the filters themselves are different in quantity and function. Again, when in doubt, listen...you should easily be able to tell which one is correct. Steve ------------------
"Old projectionists never die, they just changeover!"
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Les Brock
Film Handler
Posts: 42
From: Basingstoke, Hamshire, UK
Registered: Nov 2001
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posted 06-09-2002 03:06 PM
Paul said "In both newspaper ads and on the marquee, the name used for SR was "Dolby Spectrasound" (with the full name appearing INSIDE the DOLBY logo box." The correct title is Dolby Spectral Recording hence the Dolby SR. With the introduction of Dolby Digital the format name SR-D came from Spectral Recording Digital.
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