Canopus ADVC-300 passthrough line TBC?
 

Hello all,

I've just had to do a small repair on an ADVC-300, however, while it was on the bench I've done a few experiments to try and determine for myself if the unit has an effective line TBC.

I've got 'The Bastard' out, our machine that's deliberately kept because it will give any TBC an absolute workout, it's a 1981 model Sanyo Betamax (or should that be Betacord machine) that's been thoroughly abused and as it has very easy access to the adjustments for timings.... It's routinely and randomly twiddled with, I can also programmatically (with an Arduino) set it to sweep, random field, timings etc purely to give any TBC an absolute hot mess to unpick.

It's been a fun hour before I start posting my findings (which probably won't be until tomorrow as I need to analyse some wave captures etc) who wants to make a guess?

- It has no line TBC functionality?
- It has very limited TBC functionality (feel free to explain)
- Meh, possibly it's doing something?
- It's a fair line TBC
- It's a great line TBC

What I can say, is that it does modify the video wave form, that I can prove conclusively, for better or worse though, or no impact?

Or something else will be interesting to see what my experiments correlate with.

I would like to see a split screen of the HBI/VBI section, Do you have a studio monitor or can modify a regular CRT to display a split screen? That would be the ultimate test.

I'm using a small JVC studio monitor set in A/B switching but it does not allow split screen.

I'm going to make some captures, post up some grabs from the 'scope and diagrams.

Leave it with me, I'll check in the store room and see what's on the rack, we may have an A+B unit somewhere. If not I can probably fudge something.

Depending on sources, it's within this range. Do nothing, to do minimal.

And minimal is actually arguable worse performance. I have some good samples that showcase this (one of my 2020 pandemic projects, but I've not had time to share findings yet). What often happens is the unit struggles to hold the timing corrections. It must have a puny RAM buffer.

The ADVC-300 has another problem, however. Much like the ES10/15, it has filters that are always-on, even when "off". So it's more like high/low, not on/off. Canopus engineers, like Panasonic engineers, consider the users stupid, and they "need" some % of filtering. Such things are not new to video, or even non-video, a "protection" for users to not complain.

So what you have is this:
- cooked colors, aka bad NTSC 4:1:1, and passable PAL 4:2:0
- DV blocks
- a "TBC" that is mostly in name only, minimal corrections
- aggressive NR/filters that messes with quality

The card is garbage.

If you insist on a DV converter, get the ADVC-100, 110, 50, 55. Or the DataVideo DAC-100.

What would you suggest, in terms of capture cards?

I'll chalk that one up.

I'm not testing it for DV functionality, only as a passthrough, just to eliminate that before we wander into that as it's not especially relevant here: we need good SNR.

Remember I am feeding it horrendous, barely displayable video (with waveform captures) through to fair video as part of this.

Small pre-experiment might be easier to share by video, give me a bit.

It has sufficient jitter correction, not as good as the line-tbc in the svhs recorders or the Panasonic DVD recorders in passthrough mode. It also has useful proc-amp functions. But you should turn off all filters. The device also does not like blank spaces without movie content. Another disadvantage is the DV compression and that there is a problem with sound offset that can disturb sensitive ears but also many users do not notice as long as they do not know that it exists.

It is better than using nothing at all. If you can find a cheap device (not more than 50 Euros) definitely worth a try for the PAL capture workflow.

I'm not discussing the DV constraints and merits here, just purely using it in 'passthrough' mode. There's no DV involved in my experiments.

I've got a 'few' TBCs here, I'm just intrigued as there's a lot of conflicting information posted around the web about this device, and as I do have the equipment and knowledge to perform some experiments myself I thought it might be interesting to share.

I'll upload a video in a moment of the first thing I discovered.

RR

Do you have schematics of the unit? I don't think the box does pure passthrough. It hardware encodes all input to DV, period. All output is DV encoded.

At the very moment, I'm testing some DV gear in Win10.
I hate Win10.
@#$%&-ing Win10. :rant:

The big issue with DV boxes is that footage is lost at start/stop of breaks. I have an old family tape for testing, and the clip-show on/off nature of the tape leave a lot of footage "on the cutting room floor" (including salient moments that should never be cut by even 1 second).

https://youtu.be/Dqp3zkumQgQ

Probably a bit of language in it, I shot it and uploaded it one hit so apologies if there is!

Just a very quick and dirty mobile phone video, but I can say with almost certainty it does do something in passthrough mode.

Whether that makes an effective line TBC cannot be determined from this, but signal conditioning is taking place.

Video shows that it does 'something' in passthrough mode.

I also have the unit my collection and have done some testing with some of my test tapes.

But I'm not sure if the device doesn't convert to DV internally, even if you just loop the signal through. Are you using the ADVC controller or the DIP swiches on the unit?

I'm fairly sure this is taking place before DV conversion, however, I can not tell that at the moment.

What I'm feeding it at the moment is of such poor quality, I can not make the determination as the IQ isn't really good enough to work out what's going on!

You could very well be correct, however, that's part of the fun of playing with these things - it could well be a load of nonsense, but at least, on probabilities, we've proven the unit is NFG as a line TBC with evidence and extreme testing.

It may be easier to see if there is DV compression on the output if you send the output to capture card. If there is a lot of noise it should be noticeable.

Are you able to take a photo of the internals? There is a picture of the ADVC-100 on videohelp, showing that it uses a Philips SAA7114H video decoder (same as in the avt TBCs) and a large NEC ic which presumably does the DV conversion and filtering. Haven't seen any images of what the 300 has. Maybe it has a different A/D chip, as at least the SAA7114H does not have line-tbc/jitter stuff built in.

I'm working without access to conventional capture at the moment, I could run it through SDI here but it will add another layer of confusion. I'm in the small office today.

On the 9" monitor I can not perceive a colour difference between A/B with a decent machine, but I'm also aware (through bitter experience) everything looks good on a tiny broadcast monitor. Like the old adage about the HiFi so good, "even Zappa sounds incredible."*

Hmm... Let me have a think about what I can do this afternoon to determine what's going on.

*I'm a Zappa fan, I can take it.

Good call, I'm defrocking her at the moment.

-- merged --

Right, sorry I don't have pictures immediately available, but I believe it's a Panasonic TBC, MN673744. It's fed from the 3D Y/C IC, which is a beast.

The suspected IC datasheet is here.

There's a lot going on in one of these, across two boards.

Full 4:2:2 line (and frame sync) supported by either 16 or 32 MBit (not determined yet) of 'fast' SD RAM. It does output Rec.656 though, which might be where the party ends, but it's been fun to experiment. Datasheet seems truncated so I wonder if there was a bit of protection going on.

I'll dump some pictures and docs' I've found on archive.org when I get a moment.

Interesting thread here -> https://forum.videohelp.com/threads/...BCs-to-die-for Might have saved me a bit of time.

Hmm.. Back to the drawing board.

I used Roland (former Edirol) VMC-1 before and it never looses sync with audio even through static tape noise between scenes. Though never used it as a passthrough the diagram on its top cover shows the passthrough does not involve DV encoding, the signal goes through the ADC, then to an FPGA chip and a bunch of memory clusters and then off to the DAC and analog outputs, Another path goes to the final DV chip and off to firewire port, I don't see why the ADVC-300 should be any different, this was a common design back in that era and makes more sense to avoid multiple unnessary DV encoding decoding therefore more chips and more licensing fees.

The line TBC is weak compared to the VCR one but the frame TBC is the best I've ever seen, Never had any problem even with the bad tapes using a normal Toshiba VCR via composite. I only sold it because I don't want DV anymore, If I've known about this passthrough thing back then I would have kept it.

http://www.digitalfaq.com/forum/atta...1&d=1641677686

Probably.

Nah, there's a lot of gear chip layout variation. You can't extrapolate one from another here.

I also don't think the licensing works that way. It only consider the # of chips, and # of outputs, Anything internal on the boards wouldn't be considered multiple times.

Interesting!

Apparently there is also a switch to route the DV encode - DV decode to the analog outputs through DACs, probably for testing/evaluation purposes

Did not try 300, but I can confirm 100 and 110 both can be used without firewire, you can connect input to vcr, and output of ADVC to some other capture card. I had the same question. It is not a neutral passthrough as robustreviews says, it does "something". But what is exactly that "something" I never had time to find out exactly + I lack material/tapes to test

It does convert analog to digital, apply timing and corrections and convert back to analog, That should count for "something".

A common design means the signal path not the design of a particular product, The common signal path of that era is DV and MPEG chips are always the last in the chain followed by their corresponding ports. If an engineer back then proposed to have something like this: analog input -> ADC -> Timing correction -> DV/MPEG-2 encoding -> DV/MPEG-2 decoding -> DAC -> Analog output, he will be fired on the spot.

It's very (very) good at straightening out timing errors, it's managed to rebuild some rather horrendous PAL signals at least, it's a night & day difference A/B between the unit series and without.

That's only part of the story though, and I'm still trying to determine if it does an internal DV -> baseband conversion as part of the video output. That's indeterminate with my test gear available at the moment, and I do have other things in my life to deal with.

What I can say is, broadly (sample of three people) there's no perceptible colour difference between A/B making me think perhaps this is using the 4:2:2 on the video output? Possibly.

The documented drop-out glitching doesn't appear repeatable for me on the video output, but I've not tested that especially well, 'The Bastard' has a very crude DOC (and the threshold is easily adjustable to bypass it entirely) so it's getting a very screwy mess of a signal.

It would certainly need some explaining. :huh1:

I need to probe around and try and come up with a signal chain for this unit.