Logic Pro 8 4 millisecond gremlin

#1
I am still involved swapping files with a remote PC using ProTools, and he is definitely setup to start at SMPTE 0:0:0:0.

In order to match his co-ordinates I try to set my L8 similarly, but it defaults to 0:0:0:05.

He says that when he spots the files I send him, they spot to 4 msecs later than they should.

I don't really understand this as I thought that L9 regions wouldn't spot to PT in any case - but clearly they do.

Can someone shed light on both the 4 msecs, and the spotting?

peter
 

Eli

Logician
#2
Check your frame rate. That might be "quantizing" your position to a few milliseconds plus or minus. I'm not certain this is the problem, but it's worth looking at. Try a different frame rate and see if the behavior is any different.
 
#3
good idea ELi, but no, frame rate doesn't alter the fact that there's a tiny offset. The manual talks about avoiding absolute zero to avoid a problem called 'midnight' when some tape machines ( eg. ADAT) have to pass through zero after pre-roll.

I don't think 4 msecs offset is part of that scenario, though.

I'd love to work at 01:00:00:00 as that's a standard ( for the above reason) but it seems that my correspondent can't modify his SMPTE offset, claiming that LE has no SMPTE controls, he can't find a way to change it.

pete
 

Eli

Logician
#4
It's unfortunately true that PT LE has no smpte time base to work with, unless you shell out for the expensive DV Toolkit add on option.

And yeah, I agree. I don't think the "midnight" issue is responsible for this problem.
 

Eli

Logician
#6
I can't recall the last time I attempted to set the smpte time to 00:00:00:00. I'm not in front of Logic at the moment, but will give ti a try.
 
#7
OK here's the bottom line question:
Bandleader editing session on PT LE sends me audio and MIDI files of my keyboard performance for me to proofread, edit, replace, whatever.

The MIDI arrives at 1.1.1.1 of course, no problem there. ( it'll be 4 msecs late of course!)

1. The audio is a 2nd or 3rd take so comes at a point well into the session, and he gives me bar, beat, tick co-ordinate.

2. I do the editing and send him he updated version of the region, starting at the same co-ordinate.

If both 1. and 2. are tick-based, how much leeway is there in terms of milliseconds?
Alternatively, how many msecs is a tick?

If I am adding 4 msecs the minute I return an edited region he can of course ignore that and place the region at bar/beat/tick. But that is also inaccurate .

It seems that in the above process there is no way to ensure preservation of phase relationships ( assuming that there might be some keyboard spill somewhere, say via headphones)). Even if no spill, it's a bit unnerving to know that I can't replace my tracks accurately.

I suppose the solution is to send all regions consolidated to 1.1.1.1, which would mean his 00:00:00:05 I suppose, so he would have to nudge every region back 4 msecs.

Or I could send my regions with time co-ordinates rather than bar/beat/tick and he would similarly deduct 4 msecs.

Or would 4 msecs delay mean that audio routed vis the desk to headphones back to mike would actually be in phase? :) and I wouldn;t need to do anything about it?

the words mountains and molehills spring to mind

pete
 

Eli

Logician
#8
Hi Pete,

This does indeed seem like an unnecessarily messy and complicated scenario. To answer your question about how many ms in a tick; it depends on the tempo. The distance between ticks is tied to the tempo, whereas milliseconds are absolute regardless of the tempo.

An easy way to figure out the number of ms per tick in your specific situation is to use the region parameter box. Set the delay parameter to be displayed in milliseconds. Then mouse slide the delay value to one tick, and it will display the number of milliseconds that it is.

Good luck......
 
#10
Hi Eli - well at least it's not a generic L9 problem - it must be me.

I've tried it with interface disconnected and Core audio alone, just in case, but no change.

I've fiddled with latency controls, buffer size, the 'Smooth CYcle' algorithm and more.

Nothing changes - it always defaults to the +5 msecs.

Logic Pro 9.1.1 and 8.0.2

I'm sure it's something silly but damned if I can find it :-(
 
#11
Have you tried setting the smpte time in the tempo list rather than in the synchronization window? It shouldn't make a difference; but you never know.
 
#12
problem solved via that Apple Discussion/Logic board:

I had Project Settings/General and Preferences>Display>General open side-by side and experimented with mode switching.

When I tried to switch modes there was still an offset in other modes but where it wouldn't allow me to edit the 'with milliseconds' value, it allowed me to edit the 'with bits' value to zero, and when I switched back to 'with milliseconds' I finally got there: 00:00:00.000

thanks for sparing the time to run with me on this, Eli

pete
 
#13
erk! sorry, false celebration :-(

As soon as I move the SPL, 1.1.1.1 reverts with the 5 msec offset.
Ditto if I quit and re-launch.
The preference isn't saved and I'm back to 5 msecs offset.

What do you see in your project synch settings when you set your 'Preferences>Display>General' to <with milliseconds>?

pete
 
#14
Aha - that's it! When I have it set to milliseconds, I get that 5 ms offset as well.

I have mine normally set to the first option "with bits" and it works fine. Why don't you just leave it set to "with bits". That seems like it will solve the problem.
 
#15
Would 2 snare mics differing by 5 msecs sound out of phase?
I haven't experimented, but I have read that some producers take great care to ensure that as much is in phase as possible.
 
#17
I don't think so. If bits are longer than msecs, then it's like turning up at a theatre with a ticket for seat J24, and being told that I can sit anywhere in row J. :)

eg. If I have a song at 120 bpm and I place a region taken from bar 31/60sec of PT at bar 31 of Logic, it will go to time bar 31/60.005secs of Logic.

The imported MIDI region, starting at my 0.005 secs will be in synch.
The edited MIDI and subsequent bounce will also be in synch at 31/60.005

When I send it to him, it will 'spot' to 31/60.005 ( out of synch) and he will have to manually move it to 31/60.000.

So far so good.

But what happens if he sends me a region which runs from PT bar 31/59.995 secs?
If I place it at bar 31, it will go to 31/60.005 and go back to him as such, which he will then manually place at 31/60.000
It will then be 5 msecs out of synch.

hmm <ponders>

Having laid out out like this, I can see what has to happen.
He has to give me his time co-ordinates - NOT his bars - I have to return the edits to him and he has to deduct 5 msecs when he puts them back into the mix.

thanks for giving my space to think it through - I think I've got it but let's see what the forum brings :)
 
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