Topic: SD 744 Matrix: how long of a time shift for SBD channels? Synch 2 744s in post?

[winisp]

For the SD 744 owners who record ambient mics in two channels and SBD out in other two channels:

• Do you typically do a time synch or a time stretch when creating a 4 channel matrix? I assume the answer here is time synch but some might also do a time stretch?
  
  How long is your time synch (e.g., SBD is 2 milliseconds faster than ambient channels)?
  
  If you do a time stretch, how long is it?
  
  Finally, has anyone synch'd 8 distinct channels from the same show, all recorded to a 744 (i.e., 2 mic, 2 sbd in 744A, 4 mic in 744B)?

The info in the following thread is has all the info one might need on various matrix creation approaches, time stretching, etc (http://taperssection.com/index.php/topic,77942.0/all.html ). Basically looking for best practices on the 744 to make sure nothing is missed.

[Brian Skalinder]

Nothing unique to the 744 here, so I'll give it a go.

Time alignment between mics and SBD recorded to the same 744 will vary from recording to recording, depending on your mic location, etc.

Regarding timing between two different 744s:  if the 744s clocks are synced, there should be no drift between 744A and 744B, so you should only need to time align the start of each channel.  If the 744 clocks were NOT synced, then you'll have drift between the tracks from 744A and 744B, and will have to either chop the tracks into smaller pieces and align regularly, or stretch the tracks from one 744 to match the tracks from the other 744.

[winisp]

Thanks Brian. As always, very useful. 

Still interested in the precise time difference that 744 owners see between ambient & SBD. I have heard some one 744 owner say as much as 10 msec and I am seeing consistently 2 msec at 5 different venues based on close waveform inspection and almost zero drift across 110 minute shows. This seems contrary to a lot of variability that others report, especially relative to mixing from different sources.
 

[Shawn]

you should never see any drift when recording 4 channels on the 744.

the delay between the two signals has nothing to do with the 744 itself. it's about where your mics are in relation to the stacks. the farther away the mics are from the stacks the bigger the delay will be.

[bgalizio]

Thanks Brian. As always, very useful. 

Still interested in the precise time difference that 744 owners see between ambient & SBD. I have heard some one 744 owner say as much as 10 msec and I am seeing consistently 2 msec at 5 different venues based on close waveform inspection and almost zero drift across 110 minute shows. This seems contrary to a lot of variability that others report, especially relative to mixing from different sources.
 

The time alignment will vary depending on how far your mics are from the sound source. A good place to start is 1ms per foot away.

Like Brian said, once you line them up at the start you should be good to go. Unless you're running multiple decks that are not synched.

[winisp]

The time alignment will vary depending on how far your mics are from the sound source. A good place to start is 1ms per foot away.

Like Brian said, once you line them up at the start you should be good to go. Unless you're running multiple decks that are not synched.

Thanks. I do understand the physics behind it all so that is why I asked specifically relative to other 744s and whether other 744 users see variability in their SBD/ambient synch.. I am not seeing anything like a 20 or 35 ms disparity that you suggest for my mics that are 20-35' away from PA/stage lip. I know how to synch exactly based on waveform. It is 2 ms or so regardless of venues (Showbox in SEA, Crystal in PDX, WWU in Bellingham, and a few european venues) with the 744 I used. That suggests some other factor is at play (maybe my human error seems most obvious...) so I was trying to figure that out. I am surprised that there isn't more variablity so I raised the question.

Again, appreciate all the responses.

[Brian]

also....since you are recording all channels a 744t, you can always adjust the delay in post to get it perfect with no worries of drift.

[grayp]

john p and i spoke some about this, this weekend.  i'm a 2 channel guy but we did do a sbd/omni matrix this weekend.   when listening back you could barely hear it was out of sync.   he didn't add any delay to the 744 but said he would do it in post. 
he also mentioned the 1ft/1ms rule of thumb.

we talked about syncing the word clock to my 722 with his 4022s to give another choice but had never done it and didn't end up doing it.

[mmedley.]

we talked about syncing the word clock to my 722 with his 4022s to give another choice but had never done it and didn't end up doing it.

You can accomplish this with the new 2.34 7XX firmware. C-link now really works...I saw it with my own 2 eyes! 744 and a 722 hooked via c-link. 6 channel recording. Whether it is worth it is another story. 

http://digitalpanic.org/bittorrent/showthread.php?t=18414

[morst]

. . .(snip) stretch the tracks from one 744 to match the tracks from the other 744.

Shouldn't you shrink the long one instead of stretching the short one? Why make up bits that might be wrong when you can simply discard bits that are extra?

[Brian Skalinder]

Shouldn't you shrink the long one instead of stretching the short one? Why make up bits that might be wrong when you can simply discard bits that are extra?

If the assumption is correct that it's as simple as discarding extra bits, and that's how the software actually handles the processing, then, yes, makes sense.

we talked about syncing the word clock to my 722 with his 4022s to give another choice but had never done it and didn't end up doing it.

You can accomplish this with the new 2.34 7XX firmware. C-link now really works...I saw it with my own 2 eyes! 744 and a 722 hooked via c-link. 6 channel recording. Whether it is worth it is another story.  ;)http://digitalpanic.org/bittorrent/showthread.php?t=18414

You can sync clocks with a simple word clock cable, as well, though you don't maintain the ability to sample-accurately and simultaneously start/stop.  Even so, as long as the word clocks are synced, it's pretty easy to align the tracks even without simultaneous / sample-accurate start & stop.