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Diego

Determining drift between two recorders

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Hello everyone, 

I have some wildlife recordings that are between 6 to 9 hours in length (divided in ~40-60 minute continuous segments). I used my SD744 and threw in a Sony D100 to get an additional perspective. I did a finger snap at the beginning and end of the night to try and get them synced although I was aware it was very likely the D100 would drift out of sync from the 744 and that some post processing would be needed. The D100 has no timecode and the 744 was set at 23.98 in case that matters. 

I would like to determine what kind of drift the D100 has and would like to get some ideas on how you would do it. Also if you have ideas on how would you get both recordings synced throughout. From what I see in Pro Tools the drift might not be consistent all the time. 

Let me know your thoughts and if there is anything else I should add. 

Thanks!

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As a starting point, I would line the tracks up in pt, sync the first snap, then set the transport to show number of samples, and measure the difference in time between the end snaps.  With that value and a little math you can determine how much of a speed change needs to be applied to the second file to sync it with the first.  That will get your overall lengths in time with each other.  Then go through and listen for comb filtering to see if you have any short term variations in speed, which will have to be corrected as found.

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The 744 will be very consistent, while the offset you find for the other recorder one day may not be correct for another.  The sample clocks in cheaper recorders are often susceptible to changing with the ambient temperature, for instance.  I would suggest maybe using all 4 tracks of the 744, with the 2nd pair remoted to where you put your other recorder (via an external pre amp or even the audio monitor out of the 2nd recorder you already have) so the 2 pairs are really locked together in time.

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@Wandering Ear Yeah, I think manually seems to be the only option since the drift is not consistent. 

@Philip Perkins I used all 4 tracks of the 744, this would be a 3rd pair that I want to sync. 

How would you guys test the drift?

I was thinking of making a long (~4 hour) test file with beeps every 1 minute in pt and then record that into the 744 and D100 to check how much drift there is. Would this be a good test or would you recommend another way?

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1 hour ago, Diego said:

... since the drift is not consistent.

I was thinking of making a long (~4 hour) test file with beeps every 1 minute in pt and then record that into the 744 and D100 to check how much drift there is. Would this be a good test or would you recommend another way?

You've already stated the drift is not consistent - and it won't be anyway - so do as already suggested and take a start and end sync point to try to squeeze / stretch the (least important) second file into 'sync'

1 minute sections might help - or might just drive you mad. It depends on how much you want to rescue the 6-track and how phase accurate the multitrack needs to be.

If it was just a case of a commentary or unrelated 2-track on the D100, you'll be fine. If it's true multitrack I'm afraid it wouldn't have worked for 5 minutes, let alone 4 hours ...

Two 744s, if not linked by word clock, would be no better. Dig audio is itself a pretty good self clocker, but not good enough for true phase.

Jez

Timecode is irrelevant - it is a sample rate issue (ie 96.0000000000 vs 95.98687688799 vs drift). Everything will drift, nothing is perfect, but word clock (in its various forms) will continuously reclock and help keep sync between two or more clocks. Wandering Ear's advice really is the best you can do here - it just depends on how much discrepancy can be tolerated between the two sets.

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As I said, you can test until the end of time and the drift will not be consistent, it is affected by temperature etc.  If you aren't satisfied with the manual slip sync you can do for your 50 min segments then you need another recorder that can take the 744's word clock and sync itself to that.

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Like Mr Teas says!

Basically all digital recorders/converters need wordclock to remain in sync with other digital units.

In my experience, recording without wordclock sync, the drift won't be consistent.

Once, a colleague recorded a big concert with three 24-channel digital recorders. All three machines had wordclock cables connected, but machine no 3 was set to internal sync. All three machines recorded time code, still it rendered a lot of editing/realigning to get machine 3 in sync with the other two.

 

Cheers

Fred

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