Will an external TBC help my situation?

[Bullitt5094]

I have a Panasonic VHS/DVD now and it seems to transport my old VHS tapes well. No Jitter, noise, etc. It does have some pretty excessive bleed on bright colors. Titles/text especially. This could just be the tapes too. They are pretty old. Would a TBC help improve the picture quality or is it just to stabilize the picture and reduce video noise?

[gammer]

From what I understand, is that TBC's fix the timing of the video. For example, as your tape is played over the years, it slowly gets stretched and causes the timing to go off. Full Frame TBC's fix the input so it is correct again at the output. If you get interferance from timing then I could see that a TBC will make a clearer picture, or if you are having problems with Macrovision, then the TBC will fix the copy protection. But to get a picture with less noise, then you will need a hardware or software filter to lessen the noise.
Sometimes good TBC's can help fix 'jitter', but I have personaly found that trying a different VCR is more effective at fixing jitter then using a TBC to fix it.

[gammer]

Bullitt5094,

I should also mention that I have seen 'bleeding' when using a poor quality VCR. Once I switched to a different VCR, then the bleeding went away. Can you try a differnt vcr?

[Bullitt5094]

I never understood the "timing" thing until you mentioned the stretching issue. That makes sense.

On the VCR, I have a Panasonic ES40V that's done better with the tapes than anything else I've tried. Seems to have no Jitter or tracking problems. On that unit some of the tapes don't demonstrate the bleeding problem at all and some tapes are pretty bad. Newer, professionally recorded tapes look great! That being said, I'm considering taking back the 40 and trying a JVC HR-S5902. I actually posted another thread asking for advice/info on the 5902.

[edDV]

I never understood the "timing" thing until you mentioned the stretching issue. That makes sense.

Here is a little beginners TBC 101.

When tapes are mechanically recorded and played back (think of all the motors and capstans and reels spewing tape), the speed of playback has mechanical fluctuation (jitter) that represents itself as pixels moving about horizontally along the line. Audio recorders have WOW and flutter. Video recorders have that plus higher frequency head drum jitter.

If you were watching on a monitor that derived its sync reference from a stable source (e.g. a crystal oscillator) you would see all the pixels on each line moving around horizontally (assuming vertical was locked). This is known as timebase jitter and this is what a timebase corrector TBC corrects.

You might say, why don't I see this on my TV? Well if you fired up a TV from the 50's-60's you would see plenty of jitter if you could see a picture at all. Those sets assumed a stable picture from the TV station locked to a stable sync source. TV sets in the 70's had to contend with helical scan VCRs (U-Matic first) and adopted "fast response" horizontal sync circuits that could lock and follow the horizontally wandering lines from a VCR. Expensive sets would even dynamically adjust sync across a line. By the time Betamax and VHS hit the market in the 80's, TV sets were ready, or you needed to buy a new TV to get the VCR to work.

Zoom forward 20+years to capture cards. Capture cards also see horizontally wandering lines but they basically don't care. They get to say what analog level is defined as a pixel at a point on a the new digital line and capture whatever is jittering by as a pixel. Some cards work a bit at following the line jitter but not very hard.

So, without timebase correction you are capturing pixels that differ in horizontal position from the original video. This will still play back with stability to a computer monitor or TV but the timebase error is locked into the pixels. Any attempt to filter or correct or compress-encode the video in the digital domain will be lower quality because of these built in horizontal timebase errors in each digital pixel.

Does this make sense to you so far? I can go on.

[Bullitt5094]

Yes. Well I think so anyway. If I understand it correctly, the TBC really only corrects motion and wouldn't help me much with what I'm seeing. Am I correct?

[edDV]

Yes. Well I think so anyway. If I understand it correctly, the TBC really only corrects motion and wouldn't help me much with what I'm seeing. Am I correct?

Amplitude (luminance and chroma), black level, gamma and hue are corrected by a processing amplifier or "ProcAmp". A ProcAmp doesn't look at timebase stability, it is making fixed levels changes.

Often a ProcAmp is used ahead of or built into a high end TBC.

[edDV]

Another in the analog bag of correction tricks is a device called an "enhancer". An enhancer falls more into the snake oil category and claims to analog filter the video for better detail or edge quality.

These boxes are of dubious worth because they most often trade one problem for another. This is especially true for consumer products.

[davideck]

Nice posts, edDV.
Could you expand on this...

Expensive sets would even dynamically adjust sync across a line.

[pijetro]

You edDV, you rock!!
I've been watching you for a while now...

Is there an Analogue signal for dummies website that you can refer me to???
Where are you getting all this stuff from!?!

Again, good reading!!!

[edDV]

Nice posts, edDV.
Could you expand on this...

Expensive sets would even dynamically adjust sync across a line.

Maybe that was only a feature in pro monitors. As I recall there was a prediction of H phase velocity line to line and some form of compensation to the scan velocity similar to today's velocity compensation for wide screens. Philips has a TV feature called Dynamic Horizontal Phase Compensation. That may be what I recall.

I also recall some circuit that applied H phase correction field to field to more closely align pixels on odd and even lines. Maybe that was in a frame sync rather than a monitor.

[edDV]

You edDV, you rock!!
I've been watching you for a while now...

Is there an Analogue signal for dummies website that you can refer me to???
Where are you getting all this stuff from!?!

Again, good reading!!!

Thanks, I wish there was such a website.

I absorbed this stuff from years working in the high end broadcast video industry and also following consumer video as a hobby.

[davideck]

Expensive sets would even dynamically adjust sync across a line.

That is interesting; I wish I had seen one of these in action.

Velocity Compensation was essential in TBCs designed for Type C VTRs in order to maintain chroma purity across each line. I suspect that the correction range of these monitors must be significantly wider if they actually line up luminance edges.

That must be a neat little circuit...

[edDV]

Expensive sets would even dynamically adjust sync across a line.

That is interesting; I wish I had seen one of these in action.

Velocity Compensation was essential in TBCs designed for Type C VTRs in order to maintain chroma purity across each line. I suspect that the correction range of these monitors must be significantly wider if they actually line up luminance edges.

That must be a neat little circuit...

I'm recalling something along these lines but monitor and frame sync companies have little historical documentation on their web sites.

I think this technology peaked with frame syncs intended to take uncorrected microwaved U-matic ENG feeds (pre-Betacam). This wasn't my area of specialty.

[rbatty11]

OK.. so if I've got a very, very dark VHS video (and no, the title is not a film noir) and want to 'brighten' it up without ruining PQ.. I would use a proc amp, yes?? And I still don't know what a detailer does... (I think I finally kind of have an idea what a TBC does now).

[edDV]

OK.. so if I've got a very, very dark VHS video (and no, the title is not a film noir) and want to 'brighten' it up without ruining PQ.. I would use a proc amp, yes?? And I still don't know what a detailer does... (I think I finally kind of have an idea what a TBC does now).

Proc amp yes. If you don't want to spend the money, you can capture it and use digital levels filters. Quality will be better if you get levels correct before A/D capture.

[ronnylov]

With TV capture cards you can often adjust brightness and contrast in the settings. I wonder if this is adjusted before or after A/D capture? I use it to fine tune my VHS captures with my Terratec Cinergy 400 TV capture card (Philips SAA7134).
Can I get better results with a proc amp?

[edDV]

With TV capture cards you can often adjust brightness and contrast in the settings. I wonder if this is adjusted before or after A/D capture? I use it to fine tune my VHS captures with my Terratec Cinergy 400 TV capture card (Philips SAA7134).
Can I get better results with a proc amp?

The card settings vary by the card design. Try it and see what you get.
The controls on a true proc amp will offer better control.