Hi. I’ve seen some sparse discussion on how to tackle sound transfer from super 8 films. I haven’t been able to source a cheap projector with sound capability, so I’m looking at different options.
Has anyone made some own sound transfer modules? For example retrofitted a casette head for magnetic sound tape, or a diode solution for the light based system?
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For optical, the easiest solution is to overscan at high resolution and use the free AEO-Light software to decode the optical track. It’s pretty decent, but higher resolution scans will get you better sound quality than low resolution. So minimum you’d want to be doing 3k or so to get really good quality.
Interesting idea about a cassette head, but I would be surprised if that would work. Let us know if it does though!
I do not have any film with sound, so have not explore the option. Certainly an interesting idea.
From Wikipedia
The tape is 0.15 in (3.81 mm) wide, with each mono track 1.5 millimetres (0.059 in) wide, plus an unrecorded guard band between each track. In stereo, each track is further divided into a left and a right channel of 0.6 mm (0.024 in) each, with a gap of 0.3 mm (0.012 in).
From this site
Super 8 sound tracks. Super 8 film can have one or two sound tracks of magnetic type. At the first times, the sound was recorded on the main stripe. After, a second stripe was added as balance stripe. At seventies, the balance stripe was used as sound track with the duo system. And after, at middle of the decade, stereo projectors were manufactured (4). The sound is recorded 18 frames prior to the corresponding image.
- main track width: 0.68 mm
- balance track width: 0.13 mm
- edge to main track: 7.21 mm
- Sound track speed at 18 fps: 7.6086 cm/sec
- Sound track speed at 24 fps: 10.1448 cm/sec
- sound/picture distance: 18 frames
From the above, a stereo cassette head, using only one channel should be close enough to read the main track.
The balance track (also used for stereo) looks much narrower, and may be an issue.
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That second quote is a bit off. the balance stripe was always there on Super 8 film. Without it, the film wouldn’t sit flat in the gate and the focus would be off on one side of the film or the other. Cameras only record the main stripe, but some editing machines and projectors can record onto the balance stripe, which is not uncommon but completely crazy. The width of that track is so thin there’s barely anything there. I made some films in college that had dialog on the balance stripe, music on the main stripe, all edited in a motorized editor. It was …clunky. We had to use a crazy combination of connectors on the projector in the screening room - Mini 1/8" stereo to two RCA Female connectors. Then two RCA Male connectors to a single mono mini, which had a 1/4" adapter to plug into the amplifier for the room. That “mixed” the two together in the most rudimentary way.
But the balance track was never officially used as a soundtrack, because it was never meant to be used for that and sounded absolutely terrible. So the description from that site is misleading. The main track is where 95% of the sound you’ll find on Super 8 mag striped film is located. Occasionally there will be something on the balance track.
I wonder also if there would be impedance issues with a cassette head vs the heads used for projectors?
Thanks for sharing the know-how on the balance track, great insights.
In that case, using only the L or R head of a stereo cassette head, according to the dimensions above, should be close enough.
Good point. The cassette electronics is expecting the tape to move quicker, and is designed for the corresponding bandwidth. The film would be moving slower, and have a reduced bandwidth. For a quick test, it should produce sound, but for quality/noise, it may be best to adjust the filter to the bandwidth.
I’m assuming the idea is to use the cassette head and its corresponding electronics. Impedance may be an issue if not matching head-to-electronics, for example using a cassette head and a projector electronics.
@Ljuslykta from the new information it seems feasible… but as always, we may be missing something. I also saw that some film heads have a little spacer, like a shark fin.
If you try it, please share your findings.
If it’s a problem, another workaround might be to capture the audio in a separate pass at the cassette electronics’ native speed (using a high sampling rate) and then sync it to the video in post-production. Something close to this would probably already be required because of the 18 frame delay.
It’s a couple extra steps, but it might work in a pinch.
Thanks for all the input!
I’ve thought about this too. I haven’t been able to find anywhere any numbers on the properties (signal strength, bias, material type) but maybe some resistors/capacitors need to be replaced to match the properties of the super 8 magnetic stripe.
Sounds feasible, the question is how much the sound quality will suffer of being dropped down however many % to match the original speed.
Absolutely. It will be a while until I have time to sit down with it, but I’ll report back if I find anything.
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Late to this thread, sorry. There is a fundamental difference between a magnetic tape head and a head for film mag stripe. In all good film projectors, sound or silent, to avoid scratching, the film it is handled by its edges. It’s the same with the mag stripe head. To avoid scratching the film as it passes over the magnetic sound head, the head must completely avoid contact with the film’s image area but make good contact with the stripe(s) on the edge(s) of the film. This requires a specially shaped head face, with narrow protruding sections just wide enough to read the magnetic tracks intimately but miss touching the image area. Also unlike the intermittent picture, sound is continuous and our hearing is very sensitive to speed/pitch errors which often present as wow or flutter or both. So usually a heavy rotating flywheel is incorporated to smooth out the film speed variations as the film travels over the sound head. Then to be effective the smooth action of the flywheel must be decoupled from the intermittent film advance in a film gate. This is not easy to achieve. Then being very sensitive to magnetic fields the magnetic head needs to be somehow shielded from sometimes very strong magnetic fields generated by parts inside the projector, usually the mains transformer and any motors. So really the sound projector needs to be designed for sound from the ground up with these aspects in mind. We cant just tack on a tape head to an existing silent projector or scanner and expect good sound results, let alone expect the film to survive damage. Hope this helps.
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As I’m currently running sound films through the old projector, hoping for the best (as in, nothing coming loose - my parents did use the balance stripe for voiceover…), I remembered finding this repair/maintenance booklet:
The images have really bad resolution, but chapter 7.3 has a sketch of the head. After that there’s some data on sound amplification. But my knowledge on these things is barely scratching the surface, so I can’t tell how useful it is.
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