Film-Tech Forum ARCHIVE: random question

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Posted by Alan Plester (Member # 852) on 08-06-2016, 03:56 PM:

Hello everyone in cinema land, can you experts answer a question for my daughter who wants to know...
On old films if it was credits on a black background what made the cracklings of white?
I just know one of you will have the answer,
thanks in anticipation

Posted by Harold Hallikainen (Member # 5405) on 08-06-2016, 04:21 PM:

Is the "crackling of the white" referring to watching an old movie on TV? If so, that should not happen any more unless the video is converted to NTSC RF and sent to the TV. NTSC uses (used?) a vestigial sideband AM signal to carry the video and an FM carrier 4.5MHz above the video carrier to carry the sound. Very early TVs used two receivers, one for the video, and another for the sound. In 1948, Louise Parker patented the "intercarrier method" for television. It was realized that there is no difference (especially for vestigial sideband where the lower sideband only goes to 1.25MHz or so) between two carriers separated by 4.5MHz and one carrier with a subcarrier of 4.5MHz. In an intercarrier transmitter, the sound carrier is generated at 4.5MHz and added to the video signal, which then drives the AM transmitter. On the demodulator side (in the receiver), the demodulated signal consists of the analog video with a 4.5MHz signal above the video. That 4.5MHz is frequency modulated with the sound.

However, when you amplitude modulate a carrier, you have to be careful to not go over 100% modulation ("carrier pinchoff"). Since NTSC video uses full carrier for sync, near full carrier for black, and low carrier for white, when you combine the FM subcarrier with the video, white MAY cause overmodulation. If the video carrier entirely disappears due to the white (typically text), the FM subcarrier also disappears causing the sound to come and go as the various pixels are transmitted.

So, IF you were talking about white credits on old movies as seen on an NTSC TV, that's probably what happened. If that's not what you're talking about, it isn't!

After the fact, noticing that you are in England, you did not have NTSC television, but intercarrier was used in all analog television systems throughout the world.

Speaking of British television, 25 or 30 years ago, I saw a television program about the first 50 years of television at the BBC. It was great! They covered the Baird system, various mechanical systems, etc.

Thanks!

Harold
(who used to work in broadcasting)

Posted by Alan Plester (Member # 852) on 08-06-2016, 04:28 PM:

Wow! fast answer, many thanks for that Harrold, appreciate it.

Posted by Brad Miller (Member # 2) on 08-06-2016, 04:59 PM:

Teaser subject titles are not permitted.

Tick...tick...tick...

Posted by Steve Kraus (Member # 476) on 08-06-2016, 06:16 PM:

Alan, you need to edit the title of this thread to reflect what it is about.

Posted by Leo Enticknap (Member # 534) on 08-06-2016, 07:46 PM:

If you're watching a film projection, then white artifacts (specs, lines, etc.) could be dust and scratches that were present on the internegative used to strike the print, and were printed through - black on the neg, white on the print. That wouldn't just be in white-on-black titles, but negative scratches and dirt would certainly be very noticeable there.

Since the 1980s, internegatives were ultrasonically cleaned after a given number of passes through a printer, and so negative dirt and scratching on a typical release print from the '80s onwards was almost zero. But lab cleanliness wasn't as efficient going back further, and so you do tend to see more negative crud on original release prints of older movies.

Posted by Carsten Kurz (Member # 5396) on 08-07-2016, 01:19 PM:

Alan - can you be more specific as to what you or your daughter mean with 'cracklings of white'? When/where do you experience them?

- Carsten