blackburst, timecode, wordclock, bwf......

Posted: Tue Apr 17, 2007 3:17 pm

Hiiii all,
I'm having a problem understanding what's exactly happening in the world of sync...
This week I recorded a concert on a pyramix system, I recorded in broadcast wave (time stamped)..
I put in normal ltc (smpte time code), provided wordclock wich is coming from our trucks master sync generator, wich also generates the video sync..
The pyramix system normally needs a blackburst video sync input, but for some reason the bb signal was unreliable, thus I let the pyramix use its internal sync..
now my question: The audio is synched from wordclock, the system is getting timecode, WHY does the system need video ref, what does it actually do with that? I know bwf files actually only write tc at the beginning of a file, and need constant synching when playing back, as to not drift, but my wordclock is already coming from the same generator as the video, that should be enough right?
Can someone enlight me??????
please?

cheers,
huub

Posted: Tue Apr 17, 2007 4:40 pm

Drop-frame or non-drop? When audio works with video, the sample rate really isn't 44.1kHz nor 48kHz or any of those multiples when dealing with drop frame time code and NTSC color. I'm sure others will chime in here that are better versed when dealing with these video with audio problems.

Almost but not quite there
Ms. Remy Ann David

Posted: Tue Apr 17, 2007 8:00 pm

Yes, hello
Not familar with Pyramix. What hardware were you using?
What kind of TC? I'm assuming for production it was nondrop.
Dropframe and nondrop run at the same speed..... Video speed.
If you had wordclock from your truck, you should have used that to sync your Pyramix, and not used it's own internal sync. IMO.
Your audio was not synced to workclock or video if I understand correctly.
You used your computers own internal sync, which is good, but it may not run at the same speed as the video.

Posted: Wed Apr 18, 2007 12:55 am

Hi
Given that huub is from the Netherlands, I would assume the video would be in PAL format so the drop frame issue would not apply.

Posted: Wed Apr 18, 2007 1:17 am

You know? I didn't realize that. Perhaps he's been smoking that legal stuff?

Smoking that illegal stuff
Ms. Remy Ann David

Posted: Wed Apr 18, 2007 5:31 am

I did use the trucks wordclock ofcourse, i used the internal video sync.. Pyramix has its own hardware, its dsp and i used a madi card to interface with the (lawo) mixer..
TC was 25 fps ltc ..

Posted: Wed Apr 18, 2007 10:38 am

2 things are needed for sync, positional reference (timecode) and speed reference (Blacburst or Wordclock).

Video blackburst ensures the playback timecode will sync to the frame edge of the incoming timecode.

Word clock will lock your sound to speed but can lock perfectly or as much as a frame out from the timecode.

Posted: Wed Apr 18, 2007 8:41 pm

Quote:

TC was 25 fps ltc

But your first post stated SMPTE TC, tht would be 29.97.
Was your mistake on the post, or in the truck??? Shocked

Posted: Sun Apr 22, 2007 7:08 am

nah, smpte isnt u.s. per se, as far as i know anyway, it's all 25 fps here in europe..

Posted: Sun Apr 22, 2007 7:13 am

TVPostSound wrote:

2 things are needed for sync, positional reference (timecode) and speed reference (Blacburst or Wordclock).

Video blackburst ensures the playback timecode will sync to the frame edge of the incoming timecode.

Word clock will lock your sound to speed but can lock perfectly or as much as a frame out from the timecode.

9
Yeah, but the confusing thing in pyramix is: there's clock ref, wich can be either video or external word or internal or whatever, and there's a thing called tc reference wich is video or internal... I choose the tc source (ltc or vitc) and then i also need to set this tc reference..
according to the dutch pyramix distributor, the card has two chips, an audio chip and a tc chip, and they both need sync reference... I'm wondering where the system bases the internal tc ref on.. ltc? wc?

Moderator Joined: Apr 13, 2006 Posts: 121

When internally synced, the tc chip is most likely just using the project start and sample rate. Wordclock is a sample accurate clock, where tc is frame based, so tc can be derived from wordclock (24 frame/sec from 48000 samples/sec), or internal sample rate (offset from the project start timecode) ...or more likely, an internal crystal at a much higher rate is driving both the tc and audio sample rate chips, but that's only for internal data/logic clocking.

Clock reference, when set to wordclock, just ensures that if you are recording from a digital source you are locked to the same sample samplerate clock and not incurring dropped bits, sync errors, etc (not necessary if your are getting an analog audio feed from the truck).

If using blackburst for clock ref, I would guess Pyramix (or any DAW) would simply lock its' internal sample rate clock to a frame edge in the blackburst signal, just to ensure audio is at least frame edge accurate.

I am guessing from reading your posts, that what is confusing is the idea that clock ref can be "video" (i.e. blackburst) or wc or internal; where timecode is also a video reference and either internal or external. They really aren't the same thing even though they can both be video-relative: clock reference is just simple clocking sample by sample, or frame by frame, irrespective of time position; where tc is position info relative to the actual video's position and start time.

If you are running internal tc, then tc would just be referenced from the start of the project and stamp bwf files accordingly, where obviously external tc could start you anywhere on the timeline depending on the project start tc offset.

Posted: Tue Apr 24, 2007 5:24 pm

Quote:

I'm wondering where the system bases the internal tc ref on.. ltc? wc?

Internal sync would be WC, and the LTC is a divider of the WC.

BTW

SMPTE is 29.97
EBU is 25

Posted: Wed Apr 25, 2007 1:37 am

oh, okay.. We commonly refer to tc as smpte here, I guess that is actually incorrect..

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