Film-Tech Forum ARCHIVE: Push Pull tracks.

This is topic Push Pull tracks. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Stephen Furley (Member # 1277) on 07-22-2002, 10:13 AM:

This doesn't really seem to fit into any of the forums; Brad, if you are reading this, have you considered a new forum devoted to historical processes, film preservation, etc.

Back to the main subject, I understand what push pull tracks in their various forms are, and how they are reproduced, but I an not clear as to why the are capable of giving improved sound quality. Can someone give me an explanation please?

How widely used were these tracks for original recording, at their peak?

How widely used were push pull release prints, and between what dates were they used? I know that they weren't common, but did they ever get beyond the experimental stage?

How much better could they be than a simple, single-ended track?

Thank you for any replies.

Posted by Jeff Taylor (Member # 443) on 07-22-2002, 10:28 AM:

When you discuss push pull tracks, do you mean single or dual bilateral variable area tracks? If so the single bilaterals date from the '30's and are the original RCA Photophone track as opposed to the Western Electric variable density scheme. The dual bilaterals date from 1954 and evolved into four channel Dolby. Is that what you meant?

Posted by Richard Fowler (Member # 893) on 07-22-2002, 10:59 AM:

Push pull tracks evolved in the late 1930's, either dual variable density or variable area to improve signal to noise ratio and higher output. The "push pull" was while one track was modulating at a + value, the corresponding track was modulating at a - value; when summed together the end result was superior playback. Most push pull was done in the studio with some of the tracks double sized to cut down on the generational effects of making multiple copies for recording to keep the "ground" noise level down on the finsihed sound mix. There was some usage in some cinemas but it did not catch on. The SVA track as we know it has been around since the late 1930's with experimental stereo recording done in England and the USA...Dolby updated it with Kodak's assistance to what we use today.
Richard Fowler
Theatre & Video Products Inc. www.tvpmiami.com

Posted by John Pytlak (Member # 331) on 07-22-2002, 11:08 AM:

http://www.chace.com/chcr0699.htm

"Push-pull derives its name from the in-phase/out-of-phase relationship of the two halves of the optical soundtrack. In simplest terms, the same mono sound is recorded on a split (stereo) optical soundtrack. If the tracks are mixed together equally ("summed" in engineering lingo) the in-phase/out-of-phase signal cancels. And this is how conventional sound readers play the tracks today - muffled, distorted, almost in-audible. However, on push-pull readers, the push-pull electronics combine the two signals correctly, which yields a low distortion, high fidelity playback. Push-pull, in both variable density and variable area formats, was widely used until the early 1950's to record film scores because of its high quality sound."

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Leo Enticknap (Member # 534) on 07-23-2002, 04:05 PM:

quote:
Brad, if you are reading this, have you considered a new forum devoted to historical processes, film preservation, etc.

At least one exists, in the form of a listserv operated by the Association of Moving Image Archivists (AMIA). You don't have to be an AMIA member to join the listserv; details of how to subscribe can be found at www.amianet.org and click on listserv.

The UK Film Archive Forum also operates a similar e-mail based discussion list but membership is restricted to staff of member institutions.