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Topic: How do you know if there is noise reduction on a VA track?

Kenneth Wuepper
Phenomenal Film Handler

Posts: 1026
From: Saginaw, MI, USA
Registered: Feb 2002

posted 06-04-2005 07:14 PM

We screen many restored films that have "restored" sound tracks. The original film was MONO sound but the new release has VA or SVA tracks printed on it. How do you determine if the sound has been"stereo-enhanced" and if there is any noise reduction added?

Some tracks have directions printed on them like SR. Can we assume that any SVA track will have at least Dolby A reduction applied to it? All of the films in quesion predate varaible area soundtracks and stereo as we know it so the SVA tracks are new.

Your help is appreciated.

KEN

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 06-04-2005 08:27 PM

Ken,

Variable area goes back a long way so this is not an indicator that it has been re-recorded.

You can safely assume any stereo track has at least A-type NR. I'm sure you are familiar with looking for stereo info on the track in the non dialog passages.

There are many mono recordings where the tracks appear to be recorded all the way to the edge. These are generally mono recordings.

The A or SR markings on the leaders are a good start but certainly not reliable indicators.

You have to listen and make a judgement call often times.

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 06-04-2005 09:13 PM

The only ones that are surely mono and no noise reduction are density tracks!!

Louis

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 06-05-2005 02:16 PM

We run into the same problem many times. Why labs don't put NR format information in the soundtrack neg the way SMPTE recommends and why it is not as routine as a putting in a countdown leader is beyond me, but many times they don't, especially prints made overseas.

Sam is right; sometimes it comes down to just listening (is there such an expression as "earballing it?"). We have a small mixer in the booth that will take an earphone jack. When in doubt, I listening with earphones to the left and right channels. Having the L/R sound pumped directly into your ears will tell you a lot. Stereo vs mono is almost instantaniously identifable with phones and many times gives you a much quicker answer as opposed to hunting through footage looking at the track with a loupe trying to find differences visually.

SR vs A while impossible to distinguish by the look-see method, it can be discovered with the earphones, although more difficult than hearing stereo. If you are not decoding correctly, you will be able to detect a more strident, raspy sound in the high end of the spectrum, especially if you using SR on an A track. Just switch back and forth between both on a loud passage and you should be able to tell which one sounds more natural. Switch back and forth on quite passages and you should hear some pumping if you are not using the correct NR format.

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Richard Fowler
Film God

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From: Ft. Lauderdale, FL, USA
Registered: Jun 2001

posted 06-06-2005 09:10 AM

Mono tracks by the early 1930's had noise reduction and stereo tracks where demostrated in the late 1930's in the U.K.....30 years before Dolby / UltraStereo / DTS Stereo tracks of today [Razz]

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 06-06-2005 10:05 AM

There were any number of experimental stereo soundtracks as Richard states, but we are talking release prints here.

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 06-06-2005 01:05 PM

Also, there was dynamic gating used on most mono tracks before Dolby. This consisted mainly of shutting down the track when there was no audio present rather than leaving a big white track with no modulation on it in the middle of the soundtrack area. The light valve would reduce the actual track to a very narrow single line so as not to allow an opened white area that the cell could read as noise, especially if any dirt were to accumulate on it. This was an open ended noise reduction in that it required no complimentary decoding on the playback end. I am not sure, but I think this still may be applied on modern analog tracks regardless of the encoded Dolby A or SR NR.

Then there are those odd instances of tracks that are purposely recorded in mono (Woody Allan's MANHATTAN) where the release print could conceivably be recorded in Dolby SR or even SRD and obviously needs to be played back in that format no matter if the actual audio is mono. Again, none of this would be an issue of labs would simply mark the negatives properly as per SMPTE recommended practices. I mean, how hard is it to write a freakin "SRD" in the soundtrack area on the leaders?

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Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000

posted 06-06-2005 05:13 PM

quote: Frank Angel
Also, there was dynamic gating used on most mono tracks before Dolby.

We've got some examples of shuttered unilateral VA tracks in the archive - I'll try and dig one out and scan it at some point this week.

The bottom line is that unless the track is twin bilateral, it almost certainly doesn't have any sort of NR or processing encoded which needs a dedicated decoder in the theatre (with some rare exceptions, e.g. Perspecta tones). Play it on 01, and if your processor supports it, there's nothing to lose by experimenting with 02. I used to find that with thin VD tracks (i.e. ones on which the contrast wasn't very good, thereby reducing the s/n), it would sometimes clean them up very well without any noticeable clipping of the actual signal.

quote: Richard Fowler
...and stereo tracks where demostrated in the late 1930's in the U.K...

That would have been the experiments of Alan Blumlein, I guess. He is also believed by some to have 'invented' stereo consumer audio. He was heavily involved in developing the 405-line, 50 hertz TV standard that was the forerunner of PAL and was used in Britain between 1938 and 1984. He also worked on early radar technology, too - a busy chap!

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 06-06-2005 05:40 PM

Good point about the Woody Allen soundtracks, essentially Dolby Mono with SR. There is always the exception that proves the rule.

The narrowing of the bias line is usually called ground noise reduction or GNR. I forget exactly how it works but it needs to open a precise moment before and close right after the passage is complete so you are not aware of "here comes the big one".

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Gordon McLeod
Film God

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From: Toronto Ontario Canada
Registered: Jun 99

posted 06-06-2005 07:00 PM

Also there were some DBX encoded optical tracks as well

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 06-06-2005 08:06 PM

There was no mistaking DBX encoded tracks. If there was no decoder, the pumping made you feel like you were on a roller coaster ride.

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Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 06-07-2005 01:39 AM

quote: Sam D. Chavez
The narrowing of the bias line is usually called ground noise reduction or GNR. I forget exactly how it works but it needs to open a precise moment before and close right after the passage is complete so you are not aware of "here comes the big one".

There were various ways of doing it; the main galvanometer mirror or light valve shutters could be biased to narrow the track in quiet passeges, a separate shutter could be brought in from the opposite edge with unilateral and duplex tracks, and there was the strange Marconi Visatone track, where first one, and then a second, extra black line would be inserted in the white area of a unilateral track as the modulation of the track decreased, and then removed as it increased again.

There were at least two methods with VD tracks as well. The light valve could be biased to darken the track, (I don't think GNR was done with glow lamp recorders, but the sound from those tracks was so bad anyway that I doubt if you'd notice), or the actual width of the track could be reduced in quiet passeges; the 'density squeeze' tack. I've never seen one of theese, but there's a picture on one on the BKSTS sound formats wallchart. The darkening type can be reconised by watching the track on a rewind bench; a track without GNR well appear as a constant shade of grey, while one which has it will be seen to lighten and darken.

There are pictures of the older types of VA tracks in the post which I made on page 2 of the 'What are the sound formats on 16mm film' thread in this forum. I can't find a way of linking to it; the URL is just shown as 'http://www.film-tech.com/' wherever I am on the site, so I can't copy and paste it. I know other people have linked to previous posts; how do you do it?

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Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000

posted 06-07-2005 02:48 AM

If you're using Firefox, right-click on the link to the thread from the threads menu of whatever forum it's in, select 'copy link location', and then paste it into the UBB code link in your message.

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Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

posted 06-07-2005 03:24 AM

quote: Stephen Furley
There were at least two methods with VD tracks as well.

I am confused. I thought biasing was done only on VD tracks, as the principle of the VA is to narrow and widen the translucent part of the track anyway. Please explain for the slow-brained. Pictures welcome (or working links!).

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Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 06-07-2005 03:40 AM

Thanks Leo.

quote: Leo Enticknap
The bottom line is that unless the track is twin bilateral, it almost certainly doesn't have any sort of NR or processing encoded which needs a dedicated decoder in the theatre (with some rare exceptions, e.g. Perspecta tones).

There always has to be an exception; the sample of Dolby Stereo on the BKSTS wallchart is a strange duo-unilateral format that I've not seen elsewhere.

To return to a point raised by Sam,

quote: Sam D. Chavez
Variable area goes back a long way so this is not an indicator that it has been re-recorded.

VA certainly does go back a long way; it was used by Eugene Lauste, and you can't go back much further than that with optical sound, he was demonstrating sound on film to audiences before the First World War, so it was certainly in use long before sound reached normal cinemas. On the other hand, VD tracks were still being recorded into the '60s, and duo-bilateral ones, as we have today, were in use in the '30s.
During the '30s and 40s a new film might be released with just about any type of track, and VD and VA tracks were both in use on 'normal' release prints for a period of over 30 years.

web page

The main area of confusion today is likely to be a 'A' type print mis-labeled as SR. I've even seen quite a few Academy mono tracks labeled as 'SR', but at least in this case it's obvious that it's wrong. It's not uncommon to find 'SR' used to refer to any analogue track, in the same way that anything that's not anamorphic tends to get labeled as '1.85'

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