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smpte ebu ltc timecode syncing

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smpte ebu ltc timecode syncing

Postby jdavis6809 » Fri Aug 14, 2020 11:55 am

hello,

I have various ltc time code generator readers that can insert to video

I want to know how to sync to a reference (not video) what normally is called house code

I am only interested in syncing ltc not video

the internal xtal reference is 50ppm I want 0.1ppm

the external is twice line rate square wave

would like to lock to 10Mhz rubidium oscillator if possible

let me know what equipment I should use

regards

john davis uk
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Re: smpte ebu ltc timecode syncing

Postby James Perrett » Fri Aug 14, 2020 12:39 pm

Can we clarify exactly what you are trying to do?

You have a very precise 10MHz signal generator and you want to use it to generate linear timecode at a very precise rate. I presume that the 10MHz generator doesn't output any real time information - just a 10MHz square wave - so the timecode generator generates its own time. Do you need to start at a precise time?

What make and model of timecode generator do you have?
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Re: smpte ebu ltc timecode syncing

Postby Hugh Robjohns » Fri Aug 14, 2020 12:52 pm

jdavis6809 wrote:I have various ltc time code generator readers that can insert to video
I want to know how to sync to a reference (not video) what normally is called house code

Erm... a timecode generator is inherently referenced to video. It only exists to count video frames. It has no other purpose! (and it really shouldn't be used as a sync source, if that's your plan -- it's way too coarse for that!)

Obviously, some TC generators can run from an internal crystal and that's so that you can pre-stripe an analogue tape with code prior to syncing against a video reference.

the internal xtal reference is 50ppm I want 0.1ppm

That's either going to involve some major re-engineering of the timecode generator, or a different approach entirely....

If the device's internal clocking is to 50ppm accuracy, it's very unlikely that it's going to be capable of tracking an external clock 100x better. It's PLLs just won't have been designed with that in mind!

The sensible way to achieve greater TC precision is with a decent video master generator which can (if really necessary) be synchronised to your Rubidium clock, and then run the TCG from the video gen in the usual way.

I think it might be a good idea to explain what you're trying to achieve and why, because I suspect you're chasing the wrong thing and there will be a better way to achieve what you actually need.
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Re: smpte ebu ltc timecode syncing

Postby jdavis6809 » Sun Aug 16, 2020 1:55 pm

hello,

looks like I have the wrong tc gen/ readers to do what I want

ie timeline lynx tc gen reader and avitel tpr1040

I want to lock a tc generator to 10Mhz rubidium reference to test for frame drift

and compare other tc generators to the master

the master time code units I have looked online show master tc generators locking to video not to ltc

please advise to what to use ?

regards

john davis uk
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Re: smpte ebu ltc timecode syncing

Postby James Perrett » Sun Aug 16, 2020 3:21 pm

My first thought is that you could divide your 10MHz down to 48kHz to feed the word clock input on something like a MOTU Digital Timepiece. The DTP has a mode where the word clock controls the speed of the output while the position is generated internally.

There may well be other devices with word clock inputs but the DTP is the one that I'm most familiar with.
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Re: smpte ebu ltc timecode syncing

Postby Hugh Robjohns » Mon Aug 17, 2020 4:02 pm

jdavis6809 wrote:I want to lock a tc generator to 10Mhz rubidium reference to test for frame drift

Sorry... still not clear... test for frame drift of what, in what context?
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Re: smpte ebu ltc timecode syncing

Postby James Perrett » Mon Aug 17, 2020 10:12 pm

I was just doing a quick search on a different way of doing this and discovered this page

https://www.aesglobal-ltd.com/time-code.php

A GPS to SMPTE convertor like that will give you extremely good accuracy which means you could do away with all the kludges needed to get your existing gear working.
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