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Author
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Topic: sound-sync and MIDI
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Bart Smith
Expert Film Handler
Posts: 228
From: Hackney, London
Registered: Feb 2007
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posted December 04, 2008 02:03 AM
You can't record MIDI directly on a tape (whether it be a standard audio tape or the balance track on a Super 8 print), as it is not in any way, shape, or form an audio signal. This is a very common misconception, and is doubly confusing to those unfamiliar with MIDI as the standard MIDI port uses the same 5-pin DIN socket that was also commonly used on some older audio equipment, and as MIDI ports are most commonly found on musical/audio equipment.
MIDI is a stream of data essentially, relaying various command events between bits of equipment which use it. For instance a MIDI keyboard 'tells' a sound module/synthesizer etc. that note 'x' has been struck at velocity 'y'. When the key is released is transmits a different command to let the synthesizer know that note 'x' had been released. The synthesizer generates audio based on its interpretation of those data signals.
Getting back on track, another stream of data in the MIDI standard is MIDI timecode (MTC). It is this signal that the Korg etc. will use to synchronize itself to external devices ('slave'), or it can generate the MTC in which case other MIDI devices can synchronize to it (in which case it is the 'master').
To use MTC sync in conjunction with an audio recorder you need to get another box of tricks, a MIDI to tape sync. These come in various flavours, but the most sophisticated and suitable type for these purposes would be a MIDI to SMPTE unit.
In theory the following might be possible:
1) Your high quality soundtrack is recorded on the digital multitrack.
2) You play it back (it is the master generating MTC) and connect the MIDI out to the MIDI in of the sync unit. The sync unit generates its audio signal (derived from the MTC that the digital multitrack is generating) which you record onto the balance track using the projector.
3) Set the digital multitack to slave, rewind your film and set the projector running. The audio output is connected to the audio input of the sync unit. The sync unit converts this back into MTC, and the multitrack should start running in time. This would only work if the balance track is capable of holding the bandwidth of information in the SMPTE soundtrack which it may (or may not) be able to do.
HOWEVER...
It isn't that simple! The above example would work fine if your soundtrack was something you had composed yourself stored as pure MIDI data without the use of long samples or audio recordings. If you have simply recorded a 5:1 soundtrack off a DVD or whatever onto the multitrack in MIDI terms it would be a single event. A signal would tell it to start playing, and it would wait for another signal to tell it to stop. You would lose sync. I could go into this in greater detail but that would take too long!
So the only relatively easy approach would be to use a projector with external crystal sync such as the GS1200. In which case you would be pretty much as well off just playing back the DVD in the first place, the only real advantage that I could see with using a digital multitrack is that you could probably be able to get the soundtrack to start at exactly the correct point, and you would be able to edit the soundtrack to remove portions of it that aren't on the Super 8 film. You could isolate the portions of a soundtrack from a DVD that are found in an edited digest and stitch them together in sequence for example (but then again you could do this last bit with a computer anyway).
So yes you could do something along those lines, but it would be quite a bit of effort. The other problem is that most digital multitracks have finite internal storage, so you would only be able to fit a few movies onto it (unless you had load of hard drives that you kept swapping out).
I'm sure I've missed out some other pertinent points, I guess what I'm trying to say is that it isn't as simple as it may first seem, and certainly not at all easy with 'prosumer' recording gear like the Korg you mention.
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www.bluecinetech.co.uk
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