Got my Canopus Raptor from Egghead!

[Grigory]

Hi,

I don't have any 8 mm analog tapes, so the problem does not exist for me.
When I tried to record VHS tape into D8, there were no problems with analog to digital conversion. In this point, AGAIN, D8 camcorders work exactly as miniDV.

Concerning realtime conversion of analog recording to firewire, as I understood, the TBC is not working BEFORE analog to firewire encoder, or does not working at all. However, TBC is obviously used for recording of analog signal from the inputs.

Well, we probably have to keep this in our mind for future.

Anyway, analog inputs work as capture card much much better than RR_G.

Grigory

[Patrick]

You know, Jerry, you're really getting petty. Did I say that Keith had done any procedure that I had specifically suggested? Who cares? Geez, you're insecure.

I believe Keith has demonstrated that the TBC in the D8 camcorder has cleaned up the time base errors in the digital footage that had been copied from the original analog footage. If I remember correctly, I think I mentioned something about TBCs earlier. Did you?

If you want to take all the "credit", be my guest, fella.

You're the Man, Jerry.

[Patrick]

Grigory, if I might clarify something that you've referred to. You stated:

"TBC is obviously used for recording of analog signal from the inputs".

My knowledge of TBCs in consumer camcorders and VCRs is that they are only in use during playback of the signal, not during the recording of it.

This is probably one of the few times that I would ever be able to correct you.

[Grigory]

Hi Patric,

Glad to hear something that makes me less GREAT than I am .

Let us think little more:

1. The chip inside D8 IS able to take ordinary analog signal, with possible timebase errors and other irregularities, and convert it to DV, not loosing any frame. Many of us have checked this.
2. There are two major sources of analog signals for D8: a)input signal from another, analog camcorder, and b)analog signal read from tape with D8 camcorder itself

Case a) works very well.
Case b) sometimes has problems.

What is a difference? It is on the tape reading stage.
Well, I continue:

Hi8 and regular 8 camcorders were designed to work with analog signals. They have older design of mechanics, and were originally designed to accomodate relatively wide range of tape speed variations, to be able to read different tapes. They have a built-in recording track positioning subsystem that was designed specifically for analog tapes. The tape speed has to be adjusted to keep the heads always over the recorded track. If the speed variations are too high, the first bad thing that may happen is (apart from TV set sync loss) a signal loss because the head goes outside a track.
However, this does not happen very often, because the tracks are relatively wide, and the heads are wider. So, the signal LEVEL is kept stable, but only the frame rate or even line rate is changing a bit.
We have found that these timebase errors are easily accomodated by DV codec. Any analog VCR also adds sync pulses of standard amplitude on the output, so DV codec can use them well.

Now about D8. It WAS designed to work with D8 format. The heads are less wide, the parts are (probably) made better, so the expected variations of tape speed are lower for D8 format. Sony decided to make D8 compatible with analog tapes. However, they cannot use two systems of heads on a drum. So, it may happen that the auto-tracking subsystem of D8 is working less efficient than on analog camcorders. Auto-tracking fails may result not (only) in the frame rate variations, but in strong signal level variations as well.

So, I suppose that D8 camcorders are more sensitive to tracking errors while reading analog tapes, and this may result in frame drops or distortions.

Any other opinion?

Grigory

[Patrick]

Grigory, I may be stepping out on a limb here, but I don't agree with you.

If I'm correctly following what you're saying, you appear to be stating that tracking errors and time base errors are one and the same thing. It is my experience that they are two totally different problems. They are manifested differently and dealt with differently. Let me explain.

I won't even pretend that I understand the real technical stuff involved with the recording and playback of video, but I do have years of experience observing the problems associated with consumer video gear.

Tracking errors with 8mm/Hi8 are not usually a problem because of the auto-tracking mechanism. It works fine until the tape path alignment changes radically within the SAME record/playback device between the time that the tape was recorded and the time that the tape is being played back. Tracking errors can also occur when a 8mm/Hi8 tape is played back on a different unit than it was recorded on. Theoretically, if both units are adjusted within tolerances, there should be no problem, but I've spent enough time and money at the local Sony Factory Service Centre to know otherwise. Tracking errors can manifest themselves as excessive "dropouts", a "noise" bar in the picture, or the entire picture breaking up. The use of a TBC (Time Base Corrector) has NO effect on this problem.

Time base errors are created when the tape stretches and/or if the playback speed varies. When this is the case, the pulses on the control track are not uniform enough, and the end result is the shake or shimmy which is noticeable in vertical objects in the picture. For example, instead of the corner of a wall appearing to be rigid and straight, closer inspection will show that the edge is "alive" and is rapidly vibrating back and forth. This is because every horizontal scan line on the TV screen is slightly out of synchronization with the one next to it. A properly functioning TBC can correct these time base errors and bring all the scan lines back into sync. I can easily demonstrate this effect by turning the TBC on and off during playback on my Sony EV-S3000 NTSC Hi8 VCR. I emphasized "during playback" because the internal TBC has NO effect during the recording of a signal.

We can go on and on about this, but the point I've been trying to make in this thread is that D8 camcorders do NOT appear to correct time base errors of analog recorded 8mm/Hi8 tape when these tapes are played back directly in the D8 camcorder. However, D8 camcorders do a fine job correcting time base errors on digitally recorded 8mm/Hi8 tape. Whether this digital signal is recorded from the camera, or through the inputs, it makes no difference. The time base errors are corrected during the playback of this digital footage.

If a D8 camcorder is able to play back an analog tape without demonstrating any tracking errors as I've outlined above, but the picture does have a "shimmy" to it, I believe this has NOTHING to do with the camcorder being able to track the tape properly, and EVERYTHING to do with whether or not the TBC circuitry is being utilized.

Maybe we should have started a new thread...



[This message has been edited by Patrick (edited 26 October 1999).]