MovieStuff wrote:I think the one thing that needs to be removed from the equation is the likelihood of having 16mm prints. So many labs are dropping printing services altogether for 16mm that, should your sync sound project come to fruition, there is a fair chance that you will be limited to projecting reversal with physical splices. I only mention this because not all projectors handle splices with the same grace. If your projector is slaved to the audio then loss of sync on each splice may not be noticeable if the system recovers within a few frames. But if the audio is slaved to the projector, the possibility of noticeable jumps in the audio will be greater as each splice hits the gate and the projector stumbles. Since your goal is to have this system work on a variety of projectors, then this might be an unknown variable.
But here's an idea: All 16mm projectors have AC motors and those motors have a soft lock to the incoming cycle rate of the mains. Supposedly, that soft lock maintains a fairly even RPM on the motor making it less vulnerable to fluctuations in voltage levels. In reality, you can put a variable transformer on the projector and induce speed changes rather easily. The cycle rate stays the same but the motor will respond to increases and decreases in the voltage if they are big enough. I've done this in the distant past to do some quick and dirty transfers with a standard 16mm projector with a modified 5 bladed shutter (NTSC). Oddly enough, those changes don't seem to affect the light output in a visible way because the degree of change needed to maintain sync is so minimal.
So perhaps you could have a strap-on encoder wheel at the feed of the projector that provides a 1-F reference pulse and the projector simply plugs into a variable power supply that is controlled by the PC. The other, more nimble alternative would be a modified inverter where the PC changes the actual cycle rate of the AC power to maintain sync. Either way, the PC controls everything and the projector simply plugs in with no modification.
Roger
Hi Roger,
at our workshop (
http://artistfilmworkshop.org/) we're dealing with film at a fairly grass roots level - processing 16mm (we have a wet lab), and making contact prints on a 16mm Bell & Howell additive colour contact printer - restored by Richard Tuohy - and it works very well. Members learn how to operate the printer (through workshops) and they then go on to literally make their own prints. Currently the colour controls on the printer are operated manually (using knobs) but we'll be making it digitally programmable in the new year (to replace the original but missing punch hole tape control). Would love to actually build a paper punch hole reader (and writer) - if only for some educational value (origins of digital programming etc). But can't see myself doing that anytime soon. Perhaps when I'm finally admitted to the insane asylum I can work on that. In the meantime sticking to easier/faster to implement silicon solutions.
I take your point about splices. We do work with reversal and tape splices quite a lot. Indeed the mid February screening (for which the first iteration of a sync setup is being built) will include reversal that has been tape spliced (along with print work as well). I've been testing various mount designs for a "strap on encoder" at the feed end of the projector, and definitely keeping in mind that it needs to handle tape splices gracefully and not lose the film. I've got a sprocket wheel harvested from an old Bolex attached to a rotary encoder, either side of which are rollers to control wrap angles on the sprocket wheel. Depending on tests it may or may not require an additional clamp over the contact arc. We'll see. One design has the rollers on a ball bearing pivot to auto-balance the entrance-exit tangents of the feeding film (to minimise resistance). That's probably overkill but otherwise there in the design work if needed.
Regarding the use of a variable transformer or rate controller on the mains, that a really good idea - I'll definitely look into that for future iterations of the project.
We have heaps of 16mm projectors in the workshop, all with their own eccentricities, and we use them. And I'm not against internally modding an in-house projector. Indeed will definitely do that at some point. Would probably just get another projector off ebay and mod that. But I do really like your idea of an external rate control - where the projector doesn't need any internal mods.
The audio player software I've been writing deals with audio files at a low level - operating at the level of the individual bytes, streaming through a buffer, direct to the sound card, in which the rate is programmatically syncronised to whatever the frame rate is from the rotary encoder. At a higher level is script control over when particular sound files are to be played. For some films (probably most) it will be no more than when (at what frame number) to start and end some music - which can otherwise run at it's own original rate independant of the projector rate - others might want some particular sync effects pre-composed for a given work. For others it might be a more involved run-time mix involving a combo of sync sounds that play at projector rate, and independant music playing at it's own original rate (but otherwise synced with in/out cues). For the mid February screening none of the works will have any location sync sound that anyone is using - it's all post sound. However location sync sound is something we'll be experimenting with later in the new year.
In any case a properly controlled projector rate is definitely something desirable, and will be pursuing that in due course: for example, it would provide the ability to create those works where the image needs to follow (be edited to) pitch perfect music, as in music videos - or "music films" we might say. Or anything like that (Fantasia?).
cheers
Carl
