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99.99905% digital clock sync on MixPre-D!

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Tom Grushka
99.99905% digital clock sync on MixPre-D!
on Feb 2, 2012 at 1:44:38 am

OK, I just had to post this in a new thread...

Just did another sync test with the AES output of the MixPre-D going into the S/PDIF input on an Edirol R-44 at 48 kHz, and MixPre-D's XLR out into my XH-A1. No USB connection, so this was surely using the MixPre-D's internal clock.

After an entire hour of recording (actually, about 0.3 seconds under an hour because my sync snaps weren't right on), importing the XH-A1 audio via Final Cut capture, and lining up/mixing down the two mono files (from the XH-A1 and the R-44) in SoundTrack Pro in a stereo file and referencing to the sample counter in the toolbar... the R-44 (clocked to the MixPre-D) drifted ahead of the XH-A1 audio by...

... ONLY 1635 samples, or 0.034 seconds, about one frame at 30fps and under at 24fps.

1635 samples drift / 172786468 samples total = 0.00095% drift rate...

I know this can very from unit to unit, but that's not bad for an unlocked dual system. :-)

Way to go, Sound Devices! Now if only they could have given the MixPre-D power failover and hardware monitoring in USB mode, this thing would be almost perfect.

Raw data:

Left Channel (XH-A1 audio), end sync snap peaked at 01:00:59.62, 175661602 samples
Right Channel (R-44 audio), end sync snap peaked at 01:00:59.58, 175659966 samples
Left Channel, start sync snap peaked at 00:00:59.90, 2875134 samples
Right Channel, start sync snap peaked at 00:00:59.90, 2875133 samples (I was one off when lining up in Multitrack before mixdown)


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Bouke Vahl
Re: 99.99905% digital clock sync on MixPre-D!
on Feb 2, 2012 at 11:08:48 am

What makes you think the XH A1 has a stable clock?
I think you just got a lucky combo. Try moving one of the parts to a way colder or hotter place, see what happens then....

Bouke (who's CPU runs 4 seconds slow over 24 hours in an airconditioned environment...)

Bouke

http://www.videotoolshed.com/
smart tools for video pros


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Tom Grushka
Re: 99.99905% digital clock sync on MixPre-D!
on Feb 2, 2012 at 11:31:36 am

For one thing, it's a lot better than the Sony PCM-M10 I was going to use as my backup recorder -- I didn't measure it, but it probably lost at least a half second of sync over an hour.

What if I were to set my XH-A1 outside in the cold, and the MixPre-D inside, or vice versa? Would that be an adequate test?


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Bouke Vahl
Re: 99.99905% digital clock sync on MixPre-D!
on Feb 2, 2012 at 11:36:23 am

Well, not sure if it is an 'accurate' test, but clocks tend to change when the temperature changes, so it will tell you 'something', and it will be fun.
(It's not that this will happen in the real world, but cams might get hot when they are recording, so on short individual shots the difference might be otherwise.)

What do you use to sync up the material?

Bouke

http://www.videotoolshed.com/
smart tools for video pros


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Tom Grushka
Re: 99.99905% digital clock sync on MixPre-D!
on Feb 2, 2012 at 11:49:40 am

I will likely be using the direct-to-camera audio in most scenarios, and the direct-to-digital as a backup, in case something happens to the camera audio.

I also found the XH-A1 adds only 9 dB of noise floor as compared to the MixPre-D direct-to-digital. This may be critical in very quiet situations, hence I'll have the digital backup, but totally unimportant with louder audio. I'm making a documentary, so the audio quality is not cinematic, but it seems I'll get very, very good audio with my setup.

I'll probably be syncing manually, with sync claps, if and when I need the digital version of the audio.


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