Topic: Digital recording "slowing down"??

[acidjack]

Here is the scenario:

Two tapers both running mics into two separate R-44s (Oade Mod on each), plus SBD feed.

I gave the other taper my Schoeps source to add to his KM150+SBD source.  Obviously he needed to align the tracks.

In the beginning, my source was 30 milliseconds behind, and by the end, the difference was 100 milliseconds.  It appears my redorder was running slightly "slower".

However, when we did this on a previous night's recording from the same venue (and have done it in the past) we did not have this issue. 

Any ideas what could make my clock speed slightly slower on a given night?

Further, is the best way to fix this using the 'stretch' feature?

[burris]

Higher temperature is one thing that will make the clock run faster.  Fancy clocks put the reference crystal in a controlled "oven" to give it a stable temp.

Theres a bunch of threads on "matrixing" but yes stretch/time-compress to make it the same length and line them up. 

[kirk97132]

I've run two r-44's and they were even linked.  The clocks were not the same.  And a call to Edirol Tech got  me the same answer.  NO the clocks will not run the same.  Each unit's clock is different even on the same brand. 

[morst]

I've run two r-44's and they were even linked.  The clocks were not the same.  And a call to Edirol Tech got  me the same answer.  NO the clocks will not run the same.  Each unit's clock is different even on the same brand.

I don't think they're really linked in the sense that professional time-code gear is linked, they just connect a cable to issue start & stop commands at the "same" time. Now if your decks had "word clock out" and "word clock in" they could synch completely.

[danlynch]

I understand that the clocks are not linked, but it seems that two decks recording the same music shouldn't run different speeds to the extent that the recordings are 100+ milliseconds off per hour.  The bad conclusion is that one of the decks needs the clock to be calibrated.

[SmokinJoe]

If you call Edirol asking about a calibration I expect they will tell you that you have unreasonable expectations.  If you want them synced, you probably want devices that sync via word clock, or digi feed.  With my Alesis HD-24 and my pair of Presonus preamps (with their own A/D), I have them all hooked up via word-clock (coax and BNC's), and they sync.  If you had a V3 and 2 HD-P2s, you would run SPDIF into one, and hook the word clock up on the other.

In my experience with trying to mix things from difference sources, .100s per hour drift is typical, and maybe better than average.  When I was a newbie mixing UA-5 > H120 against R09, it was typically .300s per hour.   Sometimes you get lucky... I've had 2 UA-5's align very closely.  Just as you had 2 R-44's align closely.  But it's random.  Doing those kind of matrix's gets old fast.

You should be able to get a "poor man's sync" with 2 R44's.  If you patch the SBD channels via SPDIF from one R44 to the other, then the downstream one should sync to the upstream one.  Then you each run your own mics into the other channels, and if you wanted to align the mic sources, they would be in sync.  I've wondered if an R44 could record 4 analog channels, but sync to the clock of a SPDIF input, even though it's not recording what's coming in on the input.  If that's the case, they your pair of 4 channel decks become an 8 track combo, rather than a 6 track combo.  I don't own an R44, and so I've never tried it, and I don't know anyone who has.

[morst]

In my experience with trying to mix things from difference sources, .100s per hour drift is typical, and maybe better than average.  When I was a newbie mixing UA-5 > H120 against R09, it was typically .300s per hour.   Sometimes you get lucky... I've had 2 UA-5's align very closely.  Just as you had 2 R-44's align closely.  But it's random.  Doing those kind of matrix's gets old fast.

Heck, .1 sec is 4800 samples? Here's the latest math from my decks:
245,062,873  - 245,046,404 = 16,469 - that's 343 ms over an hour and a half.

Clocks are not comparable, they vary from machine to machine. If they didn't, SmokinJoe wouldn't need his keen Word Clock cable. But that's the proper solution. That or hack it like I do. My theory is that any two decks will have a fixed ratio, so once ya learn the conversion, then you can apply your math. I've had good results with this, and it frees me to run the microphones from the best spot, rather than near or tethered to the board as with a 4-channel unit. If the board is in a good spot, or for an on-stage pair through the snake, I do love the R44 though.