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Pilot Tone Generator for use with an Eclair ACL


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#1 Regan Luke

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Posted 14 January 2009 - 06:13 AM

I am building a pilot tone generator for use with an Eclair ACL and a Marantz PMD201 cassette recorder. Similar to this device. My goal is to have the generator place the pulse on one track (for sync) and record the sound for the production on the other track. I've found a basic schematic online, and will discuss some details with my electrician. It is necessary to have an input from the camera into the generator, for use as a double system. As well, I am wondering if the generator can be used without plugging it into the camera, using the pulse as help with wild sync. I need to find out the kind of hardware I would need to match the socket on the ACL. Does anyone know what sort of circuitry I would need to pair with the ACL? Any help would be much appreciated!

best,
-R

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Edited by Regan Luke, 14 January 2009 - 06:17 AM.

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#2 Hal Smith

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Posted 15 January 2009 - 11:05 AM

True pilot tone ( http://en.wikipedia.org/wiki/Pilottone ) is where there is a small AC generator on the camera with a 60Hz (US), 50Hz (Europe) output being recorded on a separate audio track from the production sound. That is what the standard resolvers that transfer and synchronize production tapes to sprocketed magetic sound expect. The schematic you show is designed to use a set of flash contacts. On a movie camera that would be one pulse per frame, 24 pulses/sec US, 25 pulses/sec Europe. I doubt if there's a lab already setup to resolve that signal but maybe one could be found. Pilot tone recording was pretty standard for years and I wouldn't be surprised if you can find a generator designed to attach to an ACL. My personal experience is with another French camera, a Beaulieu R16B. I owned one and had the Beaulieu pilot tone generator which worked quite well.

I would recommend not using an analog cassette recorder for pilot tone recording. Cassette recorders do not have a lot of isolation between the two channels and you may find there's too much pilot tone leaking into the other track that's recording your sound. It is possible to filter out the low frequency pilot from the audio afterwards but then you lose some bass response in your audio.

Digital recorders do not have this problem except in MP2/3 modes where the compression algorithm is looking at both channels. Just make certain any digital is in either PCM (.wav) mode or at the very least MPEG dual mono mode.

A more modern approach would be to have a crystal motor on your ACL and have either a time code DAT or TC digital sound recorder. You can get away without a time code recorder if you use a digital since most of them use crystal generators internally and therefore their record speed accuracy and repeatability is as good as the crystal motor on the camera. With slates at the head of each take you'll be able to match picture to sound with good accuracy.
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