Does TBC affect Audio Sync?

[gammer]

Hello,
I purchased a TBC-III and I'm waiting for it to arrive in the mail.

My question is, since only the video is connected to the TBC and the audio is by-passed, will this caused the video and audio to not be in sync?

For info purposes my set up will be:
19 Micron Head VCR to TBC to JVC JX-C7 Video enhancer to ATI AIW 7500 capture card.

Thanks,
gammer

[davideck]

The maximum delay through a TBC should not exceed one frame (1/30th second for NTSC), and should therefore not be noticeable.

[wwjd]

gammer,

This is off topic and is just an observation but why the AIW 7500? Your doing a lot of work to get good video to your pc but then using the AIW 7500. This card does not have on board hardware encoding, which means that you will be using realtime software encoding. That is extremely CPU intensive and will lead to audio sync and dropped frame issues. In most cases to get a good capture you will need to lower bitrate and comprimise the quality of the video.

I suggest you look for a solution that has realtime hardware encoding, either directly to mpg2 or DV avi. I recommend you go the DV avi route because then you can encode to mpeg using a quality encoder. Yes encoding is also CPU intensive BUT it does not have to keep up with the transfer process!

Canopus ADVC-100 or -110 is highly thought of. Encodes to DV avi and locks video and audio.

For mpeg2 the Hauppauge PVR-250 is well liked.

[edDV]

The maximum delay through a TBC should not exceed one frame (1/30th second for NTSC), and should therefore not be noticeable.

It depends on your ears. For pro audio-video sync 1/4 to 1/16 sub-field sound sync is often required. This requires either delay lines or resampling audio.

[davideck]

For pro audio-video sync 1/4 to 1/16 sub-field sound sync is often required.

The bigger issue is that the delay through the TBC is constantly changing because the VCR timing reference is drifting with respect to the TBC output timing reference. The range of delay will be from 0 to 1 frame, and step changes of 1 frame (advance or delay) may also occur every time the VCR frame sync drifts through the TBC frame sync.

Attemtping to maintain A/V sync to sub field resolutions under these circumstances seems pointless...

[edDV]

For pro audio-video sync 1/4 to 1/16 sub-field sound sync is often required.

The bigger issue is that the delay through the TBC is constantly changing because the VCR timing reference is drifting with respect to the TBC output timing reference. The range of delay will be from 0 to 1 frame, and step changes of 1 frame (advance or delay) may also occur every time the VCR frame sync drifts through the TBC frame sync.

Attemtping to maintain A/V sync to sub field resolutions under these circumstances seems pointless...

True, I was just talking about normal synced production standards. Like with video quality, your audio sync tolerance tightens as as your perception refines.

The test comes when doing work for others. They will be hypercritical on issues that you let pass for your own projects.

[gammer]

WWJD,

I usualy don't have sync issues with my AIW 7500. Generaly when I capture I use MMC 8.9 and I capture at 640x480 (true 4:3), I frames only to MP2, at max bitrate of 15 mbps. Then I use TMPGEnc to encode to 352x480 and at a bitrate of what is needed and filters if needed.
I have also noticed that recent versions of MMC have much better audio sync then previous versions.

I am also using a good quality sound card. And I have tried several sound cards to find one that works well. I find that this is an area that can get over looked in video capturing.

I know 'I Frames only' MP2 is not as good as capturing to AVI, but its as close as you can get with MP2 and its working great for me for converting VHS tapes to DVD.

I have had sync issues when capturing to AVI with VDub. Even if I lock Audio to Video. I think this is what prompted me to try I Frames.

[lordsmurf]

gammer,

This is off topic and is just an observation but why the AIW 7500? Your doing a lot of work to get good video to your pc but then using the AIW 7500. This card does not have on board hardware encoding, which means that you will be using realtime software encoding. That is extremely CPU intensive and will lead to audio sync and dropped frame issues. In most cases to get a good capture you will need to lower bitrate and comprimise the quality of the video.

I suggest you look for a solution that has realtime hardware encoding, either directly to mpg2 or DV avi. I recommend you go the DV avi route because then you can encode to mpeg using a quality encoder. Yes encoding is also CPU intensive BUT it does not have to keep up with the transfer process!

Canopus ADVC-100 or -110 is highly thought of. Encodes to DV avi and locks video and audio.

For mpeg2 the Hauppauge PVR-250 is well liked.

I disagree with this entire post.

The ATI AIW cards are a top quality card, and are certainly not as software-intensive as you seem to believe. In fact, they are hardware/software hybrid methods, which actually have allowed for the technology to improve as time has gone on, unlike a set and rigid hardware-only solution. Now don't get me wrong, hardware can be quite good, just as good as an AIW, but let's not distort the facts and treat hardware as being godlike.

On the other hand, DV was invented as a shooting platform. Converting from analog VHS or other traditional sources leaves much to be desired (for NTSC video, at least, PAL is fine). All the colorspace conversions take a toll on video between the source and the final DVD in NTSC DV25 (consumer). Those "video/audio locks" are also a bit of myth, it's really nothing more than a system that cannot be screwed up, any computer with any card can be equallty as good. There's no magic here.

I know 'I Frames only' MP2 is not as good as capturing to AVI, but its as close as you can get with MP2 and its working great for me for converting VHS tapes to DVD.

A high bitrate MPEG-2 with I-frames only is essentially the same as the MJPEG AVI codec, which is quite decent for a slightly compressed AVI codec. Not a whole lot different from HuffYUV in practice. Though I should mention that uncompressed YUY2 is preferable over either of these.

My question is, since only the video is connected to the TBC and the audio is by-passed, will this caused the video and audio to not be in sync?

TBC sync delay should be almost transparent, half a frame in practice, which is 1/60th of a second. I doubt even an audiophile canine would notice it.

In other words, it sounds like you have a good system. Enjoy.

[wwjd]

Actually I did not say it was not a top quality card, I said that it did not have hardware encoding and I was pointing out that on the fly software capture can be problematic and that is a fact! Yes if you are very computer literate, carefully choose bitrate, I frames only, turn off screen savers, turn off background stuff and so on then yes it is quite possible to get a capture without audio sync and or dropped frames.

lordsmurf wrote:

In fact, they are hardware/software hybrid methods

Are you specifically talking about the AIW 7500? I may be under the miss-guided notion that this particular board is software only!

It is now apparent that gammer is quite capable of making the AIW7500 work but when I commented originally I did not know that. If gammer were inexperienced I think it would be better to use something a bit easier and more bullit proof.

BTW I never tried the 'I' frame only thing with my AIW7500 and I will give it a shot.

[edDV]

Here is a consumer oriented article. The pros do expect tighter than 1/4 frame audio sync and ad agencies want it dead on.

http://www.audioholics.com/techtips/specsformats/AV_lip_sync_delay.html

The problems described assume the DVD already has audio and video in sync.

[gammer]

BTW I never tried the 'I' frame only thing with my AIW7500 and I will give it a shot.

wwjd,
Another thing I should point out is that I use a P4/2.26GHz computer that is dedicated to capturing only. Its a bare bones Win2k load with most services shut off and its not hooked up to a network. Also I capture to a 80GB 7200RPM ATA133 hard drive, that is dedicated to capturing only. It is completely fomatted except for an ATI folder that looks like it is put there when I specified in MMC that I want to use this hard drive for capturing.

I'm not sure if you have tried this set up with your ATI AIW card, but it might be somthing of interest to you??

-gammer

[wwjd]

gammer,

That is good info. BTW how old is your AIW 7500? Mine is around 4yrs old. Are there newer versions?

My pc is a 2.53 P4 running XP Home. It is my only computer so it is hooked to the internet. When I was trying to make the AIW work I did turn off everything I could but still dropped frames. I did not learn about this site until Jun 2004 and by then I had given up, went to the dark side and started using hardware encoding(ADVC-100).

I still would like to be able to say, that I got the AIW to work, so I will give it another go!

[canadateck]

I have the 7500 also,I did some really nice Captures with it"When it wanted to work".

I now use it with Windvr and Nevr get sync Problems,Mind you this is just for recording a TV show that i might Miss,Nothing I would want to keep.

I find the 7500 to be a very nice card,but is a real pain to set up.

[anitract]

Since I use an AIW for caps I'm gonna jump in on the tail end of this. I've been curious about I-frame only caps w/ AIW cards for a while. Problem is that I have a hard time seeing the point of it.

How is taking your i-frame only file and then re-encoding it any better than simply capping at mp2 w/ standard framing and a sufficiently high bitrate? Aren't you just creating more work? Isn't the AIW's mp2 capturing quality why many of us use it? Or am I wrong - is the framing not that great?

[gammer]

How is taking your i-frame only file and then re-encoding it any better than simply capping at mp2 w/ standard framing and a sufficiently high bitrate?

Don't get me wrong here, but I think the normal captures at MP2 with normal framing and bitrates are pretty good with MMC. But I did a comparison test a while back, and I found that the I-Frames converted with TMPGEnc looked better. It was a better looking picture. Also, the other reason why I go the I-Frame - TMPGEnc route, is because I like to use the TMPGEnc filters to clean up some noise on the VHS captures. I don't like to use MMC's Video Soap. I find it just blurs the picture as apposed to cleaning it. Besides capturing to MP2 slightly softens/blurs the pic anyway.

Aren't you just creating more work?

Yep. But I think its worth it.

Isn't the AIW's mp2 capturing quality why many of us use it?

It's why I use it. I think MMC does a great job of capturing on the fly. I mainly use that option on my second capture computer when I want to use it as a PVR. Also, if I create SVCD's, I find MMC does a better job at SVCD's then capturing I-Frames and converting to SVCD with TMPGEnc.

Or am I wrong - is the framing not that great?

The 'framing' with MMC is fine. Its the clarity of the picture where I notice a difference.
I use 640x480 because it is a true 4:3 ratio capture.

One area that you will notice a quality difference is in creating VCD's. Try capturing direct to VCD with MMC. Then try capturing 640x480, 15MBps, I-Frames and convert it to VCD with TMPGEnc. The later will yield much better results.

[anitract]

Cuirous if you saved any caps from that comparison. I'd be interested in seeing the difference. If you could place a % on it, how much of a gain in picture quality would you say you got from I-frame over standard?

[anitract]

So there is a *slight* delay in full-frame TBCs...what about TBCs in things like JVC VCRs? Any delay introduced there?

[Cornucopia]

Yes, there's a full frame delay (~1/30 sec.) with either External or Internal (to the VCR) TBCs. No getting around that.

If the TBC is full-featured/high-end, it may also have a compensating delay line for the audio so it will end up synced again.

You should check the owner's manual of any particular TBC models you're interested in to see if this is available.

Scott

>>>>>>
you can also get external, compensating boxes for audio only if you've already bought a TBC without one. Google "TBC" "Delay" "Audio" "Compensation" "Line" or some similar combination

[anitract]

Hmm. Would be nice to find out, since I use both full-frame and the jvc at the same time. Though I don't perceive any sync loss...

[davideck]

So there is a *slight* delay in full-frame TBCs...what about TBCs in things like JVC VCRs? Any delay introduced there?

For line based TBCs, several horizontal lines at most; probably less than a millisecond...

Yes, there's a full frame delay (~1/30 sec.) with either External or Internal (to the VCR) TBCs. No getting around that.

This is incorrect...

[payton34]

Hi all,

I have a Data Video TBC 1000. In the manual it does not say why, but instead shows the proper cable hook from source VCR to TBC 1000 and to your capture device. The diagram shows running the audio cables from your source deck thru the TBC 1000 to your capture card. I have captured with this configuration and have also captured with my audio cables by passing the TBC 1000 and going directly to my capture card.

I have not detected a loss in audio/video sync either way.

Would a possibe advantage of not passing your audio thru the TBC 1000 be that your audio signal might inccur less noise by virtue of not having to go thru another device in the analog chain as it gets converted from analog to digital?

or....

Would I not be safer to just simply run my audio cables thru the TBC 1000, and not by pass?

By doing it this way, would I not be syncing up my audio perfectly with my video?


Thanks

[anitract]

Good question. *awaits answer* If no one knows, maybe someone would volunteer to contact DataVideo.

[davideck]

Would I not be safer to just simply run my audio cables thru the TBC 1000, and not by pass?

The TBC-1000 only has a 4 output audio pass-thru distribution amplifier.
If you don't need multiple audio outputs, then there is no reason to send the audio through it.

[anitract]

I think what he's getting at is that perhaps if you send the audio through it, it might have a built-in re-sync or something.

[payton34]

EXACTLY!

[davideck]

The TBC-1000 does not include an audio delay for compensating the video delay.

[payton34]

So....

Do you think there is merit to the idea of by passing the TBC 1000, and keeping the analog audio source as clean as possible before conversion?

Thanks,

[davideck]

Yes.

[gammer]

I received my Leitch TBC-III VT2500 TBC in the mail yesterday. I did a couple of test captures using it. I did not notice any sync issues with my captures. So the delay is so small, its not noticeable.

It does a nice job with some of the VHS tapes that I previously had troubles trying to capture.

Unfortunately it didn't come with a RJ-11 to DB25 serial cable, which is needed to communicate with the card to take advantage of the TBC software. I beleive it has some kind of proc amp features.

Anyone know where I can track one of these cables down?

Thanks,
Jeff

[lordsmurf]

So....
Do you think there is merit to the idea of by passing the TBC 1000, and keeping the analog audio source as clean as possible before conversion?
Thanks,

I don't think it matters.