8MM-16MM FORUM WORLDWIDE

Dan, there's been a hit-and-miss phenomenon among our colleagues as far as whether or not they can get the square wave to work direct from a sound card or other playback device. There might have been a wiring problem, but I did try the 23.976 Hz pulse wave from a couple of different devices and couldn't get the GS to accept it. Others have succeeded. My guess is that the electrical characteristics of the audio output of these devices are dissimilar, and some make the GS happy and others don't. So I would encourage you to make up that cable and try it!

Since my "direct" attempt failerd, about 6 years ago I bought a Pedro box that's no longer listed on his website: the P1008GS-P. At the time I bought it as a lower priced solution (about 99 Euros, compared to 2-5x that for the other units) to keep all the audio and sync together in the computer. It accepts any waveform at all of sufficient amplitude, so I use the computer or a CD player with a wave file containing short bursts of a 1Khz tone spaced for the correct framerate. For 23.976 and a 48Khz wave file, that's one every 2002 samples. Then Pedro's box hears that input and converts it to the control square wave, which the projector "reads" just fine.

Very strange things can happen with sound sync even from studio DVDs if they did weird things with sample rate pull-up or pull-down or just had a little "drift." And that's after you account for discrepancies between the cut of the film print in hand and the video's cut! The worst part is that you'll never know these problems are present until attempting to run the projector with the digital soundtrack.

Now I would caution you that while recording from a VHS tape may possibly work, there's actually nothing locking the picture to the sound once it leaves the VCR. Better would be to digitize it with a device that clocks to the video frames, such as an old Tascam DA-88 with the SY-88 sync card - you actually feed it the video source and it locks the master clock to it. Then you put the audio data into your computer, play the pulse and soundtrack to different audio output jacks, and you go from there.

Another thought. How you go about this has a lot to do with how much trial-and-error you're willing to put up with, and how much sloppy sync you're willing to put up with.

But since the film you wish to re-record already has sound, the best way to re-dub it is to do this rather tedious procedure:
1 - make sure each reel has a clearly marked start frame
2 - record the sound of each reel into your computer using the pulse sync from the computer; that is, they're clocked by the same device.
3 - acquire the desired replacement sound, and get it into your computer
4 - using a multitrack sound editor in your computer, match the replacement sound to the recording you just made from your reels. This will also give you the means to correct anything spliced out of your print. So you're essentially editing the two to line up perfectly together. I create a separate 'edit' session for each reel.
5 - Now mute the original film audio and dub the new 'cut' back onto your film print using the pulse system.

That's a lot of work, which is why I've never done it for a whole feature...