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Old January 4th, 2002, 02:13 PM   #1
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Any comb filtering in DV? y/c, composite, firewire

I've just upgraded my tube and have gotten into the technical side of that and I'm wondering about the DV format.

When shooting live, is the video signal NATIVELY a digital, composite or s-video signal?

What about after it's on tape? There, it should be a digital signal. no?

My question is where are the comb filters?

As an output we've got choices on where to view from. RCA, s-video, firewire. But some of these signals have to have been processed. Right?

Again, I'm wondering about the DV format ... is it truly y/c or is it a composite signal that gets cut into y/c on playback?
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Old January 4th, 2002, 03:44 PM   #2
 
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DV is exactly what the name says, a Digital Video signal. There's NOTHING analog about it...composite, component, y/c, rgb, whatever else, are all analog signals. DV itself is processed, re: compressed 5 to 1 b4 making the digital bit stream. It's the digital bitstream that gets written down on tape and/or sent to a computer HD for storage and editing. The software codec(one in the capture device and one in the playback device)converts the digital bitstream back into analog rgb display signals for you to look at, typically in a VFW AVI format.
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Old January 4th, 2002, 03:48 PM   #3
 
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I suppose somewhere between the CCD focal plane and the software codec, there's an A to D (analog to digital) converter that takes the analog signal from the CCD and turns it into a digital bitstream, also multiplexing in the digitized audio data, which has also gone thru an A-D converter.
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Old January 4th, 2002, 04:33 PM   #4
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Thanks Bill

But once it leaves the digital domain, is it in y/c? Or is it composite?

Does the cam do a separation into y/c from composite? If it does, I'd rather output through the rca jack and let my TV do it's thing.

Or is it in y/c and the cam does it's thing to put it out in composite?

I'm stumped because my old Laser Disc player has both comp. and y/c outs. The format is in composite, so you actually get a better image through the composite signal if your tv has a good comb filter. S-video out from the deck uses the comb filter in the deck, which may or may not be as good as the one in the TV. 80's vs. 90's tech.

That's why I'd like to know how the signal is handled.
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Old January 4th, 2002, 05:14 PM   #5
 
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My understanding is that you can't do better, in terms of video quality, than firewire(ie DV). S-video(RGB component) is less perfect and composite is the least perfect. (how's that for subjective adjectives?) I suppose the analogy is like SPDIF(digital) audio vs analog audio signal. For transmission between components, digital signals are lossless, ie not subject to degradation due to line noise. Therefore, I would assume it's best to decode the digital signal as close to the analog output device as possible. I suspect in the real world, it really doesn't matter. Someone else in this forum probably knows better than I. I can tell you that when working with multi-generational file copies, you're much better sticking to DV until you're ready to "print" the final version. Some NLE's work with the Y/C components, like Ulead's MediaStudio Pro or FCP, and allow you to offset and bias the y/c values before outputting to final. Since DV format is truly not a "native" viewable format, I'm not sure why you care whether it's stored as digital y/c values or rgb. I believe, however, that the digital data is y/c. The only way to view DV is to decompress and reformat into whatever analog output signal you want. Comb filtering applies to a rasterized TV signal, so should be applied at the NTSC monitor, not the camera.
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Old January 4th, 2002, 06:54 PM   #6
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Don't worry, it's not composite (thank God). In fact I beleve it is component but I have yet to see any DV devices (consumer level) with a component output. The days of LaserDisc technology are long gone. Anyway, just look at the picture through S-Video. I don't care how good a comb filter you have, there is no way that composite could match that! There is always a bit of dot crawl or severe bleeding somewhere in the picture with composite. I have never seen a composite picture that I liked. I like DV.

Also, try to think of DV like DVD, which is also digital video. They are different formats, but accomplish the same thing in the same manner. DVD can output component. No need for comb filters there!
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