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Variable Tape Speeds?


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#1 Charlie Seper

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Posted 15 August 2005 - 03:40 PM

Has anybody tried this? I've never had a camcorder apart before so I don't know much about the gear inside it. But on audio tape decks you can adjust the playback/record speed by turning an adjustable resister either physically on the transport takeup motor or in-line with it. I would imagine anything that turns tape has to have a way to adjust the tape speed, as they drift a bit over the life of the tape deck. Thus, I would assume that any camcorder will have an adjustment screw for adjusting the tape speed. If so...why couldn't you take a standard 30ips cam and take the speed down to 24ips? More to the point...anybody got an old camcorder they'd like to try it on? :D
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#2 Luke Prendergast

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Posted 15 August 2005 - 05:24 PM

Works with analogue audio because it's a continuous waveform rather than the stream of discrete frames/fields that is video. Every video receiver expects to see frames/fields at a particular fixed rate. Try plugging a PAL (50i) signal into your NTSC (60i) set for a very rough idea of how well it wouldn't work. Color encoding is different too, but you get the idea.
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#3 Charlie Seper

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Posted 16 August 2005 - 03:19 PM

I know what you're saying, but that's not what we'd be doing here. I'm not talking about playing back the signal on a TV monitor or anything. I'm simply talking about slowing the tape speed by an exact 20% during both recording and playback. I'm not sure what the results would be on interlaced video, but I would think that a cam such as a GL2 that can already do 30p would essentially give you a standard 24p like this. If you then take that footage into your computer via firewire into an editing suit that accepts 24p footage (and of course many of them do now) then I'm really not sure that there would be a problem with it.

It would be easy enough to do a test with providing you could find the adjustment resister. I would just record a 420hz audio signal into the cam first and then use a strobe tuner to monitor the playback frequency as I turned the screw. When you hit 350hz you're at 24ips.

The big question to me is what this would do with interlaced footage. I don't see any reason why a cam wouldn't record/playback interlaced footage at whatever speed you set it at. The thing is, when you try to bring 24ips interlaced footage into your editor that's looking for 24p what will it do? I think it would probably accept it okay. I'm not sure though. Guys that can't do 30p to begin with may be out of luck. But I really don't see the problem with taking a 30p cam's speed down to 24p. Maybe I'm missing something though. I really don't know that much about it. But as long as you use a good strobe tuner and make sure you've adjusted the speed by EXACTLY 20% then I don't see why it wouldn't work.
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#4 Phil Rhodes

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Posted 16 August 2005 - 05:28 PM

Hi,

This wouldn't even nearly work. The electronics scanning the CCD would still be running at whatever rate it's supposed to rate; all you'd do would be to produce a completely unreadable tape with enormous azimuth problems. The speed of the tape has almost nothing to do with the frame rate.

Phil
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#5 Charlie Seper

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Posted 17 August 2005 - 11:26 AM

The speed of the tape has almost nothing to do with the frame rate.

Phil


I don't know much of anything about digital electronics but it just dawned on me last night that there had to be more to it than the tape speed. I say this because of the way sound is sampled. Obviously you can sample sound at whatever rate you want without the need of moving tape or even a moving HD. You could use a Flash Drive or even burn to ROM or RAM that isn't moving at all. So the speed of the storage medium has nothing to do with sample rate of digital sound. It would then seem logical that it would have nothing to do with visual optics either.

Dumb one on me. :blink:

Edited by Charlie Seper, 17 August 2005 - 11:28 AM.

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#6 Phil Rhodes

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Posted 17 August 2005 - 11:36 AM

Well, you learned something! :)
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