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Old March 30th, 2005, 08:22 PM   #1
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Double system synch sound and sampling rate

Just brainstorming a bit and wondering about how one might capture multiple channels of synch sound as separate tracks without mixing on the set, using a typical miniDV camcorder with 2 or 4 channels of sound plus a separate stereo CD or miniDisk recorder as well to give a total of 4 or 6 channels of synch sound to mix down later in post. Are there any issues involved in holding synch on such a strategy when combining material from the camera recorded at the DV standard 48k sampling rate and the concurrent sound recorded at the miniDisc standard 44.1k and exporting them at 48k in the final product? What happens if you capture the DV at the standard rate and then when editing in Premiere or Vegas bring the 44.1k wild audio into the mix as-is - will it still have the same running time as when recorded and maintain synch with the out-of-camera audio and video? Wondering if the fact that the output of the final edit will be 48k will change the timing on the tracks mastered at 44.1k so sounds from the separate recording no longer run at the same rate in the final edit as they did when recorded? Does one need to first import the 44.1k tracks into an audio editor like Sound Forge and resample at 48k before bringing them into the video editing software so the timing doesn't change or does editing software like Vegas and Premiere handle those sort of adjustments automatically?
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Old March 30th, 2005, 09:11 PM   #2
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Most editing programs handle sample rate changes properly and without hassle. Vegas definitely does it.

I think Premiere does it. If not, it's not a big deal to use a program to convert the audio. There are various batch processing tools available that can save you button pushing... old versions of sound forge have them. The may be some freeware batch processing tools.

Your sound will maintain the same running time in both programs.

2- Will the sounds maintain sync?
The clocks on mini-disc aren't perfect, so expect it to drift 1 frame every 15 minutes in comparison to mini-DV. You need to resample the audio without pitch shifting to compensate. If doing long takes, slate at the beginning and at the end.

Slate = the clapper board you see on film sets. When the clapper hits the slate, it makes a distinct audio peak that is easy to find and sync up. For things that record video and sound, look for the moment where the clapper first makes contact with the slate.

3- 4 channels of sound generally isn't that great quality. The recording is at lower bit depth (12 versus 16) and 32khz sampling instead of 48khz. Capturing may also require two passes. Scenalyzer may be able to do it in one pass.
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Old March 30th, 2005, 09:35 PM   #3
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<<<-- Originally posted by Glenn Chan : Most editing programs handle sample rate changes properly and without hassle. Vegas definitely does it.

I think Premiere does it. If not, it's not a big deal to use a program to convert the audio. There are various batch processing tools available that can save you button pushing... old versions of sound forge have them. The may be some freeware batch processing tools.

Your sound will maintain the same running time in both programs.

2- Will the sounds maintain sync?
The clocks on mini-disc aren't perfect, so expect it to drift 1 frame every 15 minutes in comparison to mini-DV. You need to resample the audio without pitch shifting to compensate. If doing long takes, slate at the beginning and at the end.

Slate = the clapper board you see on film sets. When the clapper hits the slate, it makes a distinct audio peak that is easy to find and sync up. For things that record video and sound, look for the moment where the clapper first makes contact with the slate.

3- 4 channels of sound generally isn't that great quality. The recording is at lower bit depth (12 versus 16) and 32khz sampling instead of 48khz. Capturing may also require two passes. Scenalyzer may be able to do it in one pass. -->>>

Thanks for the reply

1 frame in 15 minutes is more than acceptable for correction in post I would think. I can't imagine a shot running that long without at least some reaction or beauty shots cut in - gawd how boring! - and each cut would be a chance to bring things back into synch if needed

Very familiar with the use of a slate - I've done some production back in the dim past, back in the analog days of the early 80's and now looking to move back into it after a 20 year hiatus.

The lower quality of 4 channel / 12-bit sound in camera is exactly what got me speculating about double system - wondering how best to go about it if I wanted to put 3 or 4 mikes on various talent and record them separately to mix down in post rather than mixing "on-the-fly" to the 16-bit 2 channel stereo during the shoot, perhaps getting the two principles on the in-camera tracks and other talent or synch background sounds like live music on a separate recording to be mixed in post. Or perhaps a performer like a dancer during a live stage performance where a CD is providing their music - it seems it would be better to transfer direct from the music source later in post rather than try to tie in to the sound system and capture the music to the DV tracks during the performance itself, fading the location sound down under the off-CD music track during the performance sequence and bringing it up again for the audience reaction at the end.

Steve
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Old March 31st, 2005, 07:44 AM   #4
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The movie "Muliplicity" was shot using a unique combination of ProTools systems and video compositing. A Pro Tools 002Rack would give you 8 channels minimum (16 if you used the lightpipe) right to HD. Sample rates would be 44.1, 48, 88, 96, you name it.

The 002 will sync to external clock. If you use a house clock, the problem would be how to get the sync signal into the camera. I don't know what the issue might be for getting camera sync (smpte) to the 002R, but I'm prety sure it can be doen with some extra gear and software.

Regards,

Ty Ford
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