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Old January 4th, 2005, 12:09 PM   #16
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Basically, the do a rock-solid job of transcoding, while freeing up your camera, at a fraction of the cost. The advc-100 worked great for me. Still have it, I only put it aside when I got my dsr-11, which I now use. They also generate bars, and the advc-100 will "bypass" macrovision - NOT that I am advocating that course of action. The advc-300 also does some nice clean-up work with old footage.
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Old January 4th, 2005, 01:10 PM   #17
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Thank, Richard. Let me quiz the brains, here:

"[T]hey do a rock-solid job of transcoding ..." Do you mean they do a better job than the XL2, or other comparable cam? If so, better how?

"I only put it aside when I got my dsr-11 ..." So these converters are also aimed at buyers without some other standalone converter ... that explains why they're popular (they're so much cheaper than such a deck).

"The advc-300 also does some nice clean-up work with old footage." Yeah, I read up on that, on Canopus's website. I'm curious about this function. Does this "cleanup" happen before the conversion to digital or after?

Can anybody tell me how, specifically, this ability differs from what I could accomplish in the NLE du jour? E.g., why a hardware solution rather than software?

JS
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Old January 4th, 2005, 02:43 PM   #18
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"Rock solid" meaning they (Canopus) don't drop frames, or lose synch as some of the other brand transcoders do. (Particulary the low end brands) The canopus also use an excellent codec.

Yes, they are cheaper than a new deck, or cam. Less wear and tear on your cam or deck too. (Though a simple pass through is not as harsh cause the heads aren't spinning) BUt more importantly, they allow you to use an analog deck that you may already have.

The cleanup on the advc 300 happens BEFORE the conversion, utilizing tbc. Thus, it is a 'hardware' correction, rather than a software one. This is important if you have a lot of legacy vhs, or hi-8 stuff to transfer, that may have gotten a little 'unstable'.
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Old January 4th, 2005, 03:06 PM   #19
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I haven't used the A-to-D converter in the XL2 yet. Have you seen it drop frames or lose synch? Do you think that the converter in the XL2 may be somehow less robust or capable than a peripheral job like Canopus's?

Do you think, generally, that Canon's codec might be less desirable somehow? If so, how?

"BUt more importantly, they allow you to use an analog deck that you may already have." Ahh, good point. I haven't invested in a DV deck---I bought a FireStore FS-4 instead (now if it would only get here!) ...

"The cleanup on the advc 300 happens BEFORE the conversion, utilizing tbc. Thus, it is a 'hardware' correction, rather than a software one. This is important if you have a lot of legacy vhs, or hi-8 stuff to transfer, that may have gotten a little 'unstable'."

I assume "tbc" means "time-base correction." Very generally speaking, how does a hardware correction improve image quality in an analog-to-digital conversion? What's unique about the conversion happening in hardware? Any info you can share will be more than I know.

JS
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Old January 4th, 2005, 03:16 PM   #20
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quick search

At http://www.jamesarnett.com/2-3-3.html, I found this:

"TIME BASE CORRECTION

"When you hit pause on your VCR, the frozen image is a little jittery. This is because US household current is alternating from positive to negative 60 times a second (60 hertz) and the image (the frame made up of two interlacing fields) never stabilize completely because they are never on the screen at the identical moment. Time base correction stabilizes still frames by locking down the two interlacing fields together, into a stable frame. A time base device references the time code and uses it as a handle to lock the two fields of a frame together, so cuts do not glitch between fields. By phasing the time base device, control over color is achieved so you can correct color, hue and tint. A time base device is not a standard feature of VTR's. It's an optional, and usually external gizmo that costs a bit extra. It also doesn't work on your video tape if you haven't "striped" or encrypted your tape with time code by running it through a time code generator. Expensive VTR's and audio equipment have time code readers so they can be interlocked with one another. All this crap is eliminated by digital formats that automate most of this techy stuff."

Is this what you're talking about in hardware correction?

JS
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Old January 4th, 2005, 03:32 PM   #21
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Riiiiight.... The Advc 300 does this to the signal before transcoding to DV.

I don't think a canopus advc codec is superior to Canons. Just a little different. It is superior to say, Microsofts, or Dazzles. I think Adam Wilts site has a comparison of various codecs.

Your Canon XL2 will not drop frames when transcoding. But other, less expensive transcoders can and often do. Particularly the Dazzle Hollywood Bridge, or other less expensive brands.
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Old January 4th, 2005, 03:54 PM   #22
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OK. I get it. This gives me a clear picture (sorry) of "why these gadgets?" and "what's cheapest?"

Thanks!

JS
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Old January 4th, 2005, 04:53 PM   #23
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The main thing that an separate converter does is give you some of the functions of a proc amp i.e. the ability to tweak levels and gains before the A/D conversion. DV uses 8 bit samples and runs them through a JPEG like compressor which throws out 2 bits of information for every one it keeps. These are not recoverable. To insure that the best use of the this reduced number of bits is made it is important that the A/D converters be properly "loaded". If, for example, you are playing back an old tape which has aged to the point that the output is reduced the external converter gives you the option of increasing the gain before A/D conversion so that the coverter is properly loaded.

TBEC looks at the phase of the color burst at the beginning of each line. From this it can tell the rate at which the head is spinning. It uses this information to adjust the sample rate such that there are exactly 720 (luminance) samples taken per line. In this way it compensates for slight irregularities in the head speed over time and for the fact that the head may not be running at exactly the right rate on average. This is very important for mainitaining the proper phase relationship between the color burst and the chroma sub carrier and is responsible for the ability to keep colors true and make many generations of copies without degradation. Thus both the external box or a video camera must have the TBEC circuitry. Whether a particular external box has better burst phase recovery capability than a particular DV camera I cannot say.
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Old January 4th, 2005, 05:10 PM   #24
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Thanks, A.J.

I wonder sometimes about the components an OEM like Canon builds into a camcorder. At $4k, you'd think its A-to-D converter would rival whatever Canopus ships. But it has to share room with a lot of other circuitry, so maybe the cam's specs can't match a dedicated device.

Since I'm not a pro shop, but simply want the cleanest digital copies I can make of the usual raft of analog tapes, I'll stick with the XL2 for now.

As far as copy-protection goes, I found this in my cursory web search, at http://tangentsoft.net/video/tbc1000.html:

"At its most basic, a TBC is a device that continually digitizes frames of video and spits them back out in analog format. This accomplishes two things: it re-generates all of the non-picture portions of the video signal, and, if the video frame timing is off, puts the frames back onto a precise schedule. TBCs were invented to correct timing drift in videotape systems; tapes stretch, heads don't spin at exactly the same speed from machine to machine, etc. TBCs have other uses, too. For one thing, since they rebuild the non-picture portions of the video signal, they get rid of troublesome copy control signals like Macrovision . . ."

JS
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Old January 4th, 2005, 07:59 PM   #25
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advc-100

you mentioned that you where looking for one "advc-100". I have one for sale for $200.00 shipping included.. Just thought I'd throw it out to the thread.. thanks..
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Old January 4th, 2005, 09:39 PM   #26
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John,

That is a pretty good description of what the old TBECs did. They digitized using a clock derived from the color burst and wrote the samples into a buffer at the rate they came off the tape. They also clocked samples out of the buffer at exactly the correct rate and converted them back to analog. If the tape was running too fast samples came in faster than they were being taken out and the write pointer would move closer to the read pointer. This was sensed and fed back to the transport servo telling it to slow down. When the tape was being transported too slowly the read and write pointers would move apart and this was sensed and turned into a command to speed the transport up. The results were that the transport ran at exactly the right speed on average though it might run too fast or two slow for brief periods and that the video came out locked to the studio reference. In capturing digital video we don't care if the transport is running fast or slow as long as we get the requisite number of samples per line and we don't want analog signals anyway so the D/A and servo bits are eliminated.
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Old January 4th, 2005, 09:57 PM   #27
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Richard & A.J., thank you for the clarity of your posts. I learned a lot today, and that's often a painful experience for me ... :)

JS
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