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recording latency, overdubs, delay compensation, phase
Old 3rd March 2007
  #1
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recording latency, overdubs, delay compensation, phase

Hi,
I just realized that the increments of nudge and track object delay in Logic are not fine enough to truly line up the phase of an overdubbed track. Say you record metronome clicks from a track of recorded metronome clicks and try to line up the two tracks. Your soundcard has some latency which has to be compensated for, so you negative delay the wave file that was just recorded in the arrangement. The problem is that the increments of "tick" and track object parameter "ms delay" in Logic are not fine enough to really line up the phase in the case of say, a kick drum (some flangey sound remains however slight, and obvious). I haven't tried setting the format value to "frame" yet, is this finer than "tick"? (a SMPTE frame is 80 bits, and there are subframes..) it seems a vinyl spinning DJ could most likely line up the audio better than I could in Logic...hmm.
Anyway its an audible situation .
When doing parallel compression for instance, I suppose the dry and compressed signal always have to be recorded in the same take to preserve time / phase alignment between them. Can anyone suggest a more accurate software tool for nudging audio? I use Ableton a bit, and I think seems to let you "zoom in" enough to make a phase accurate track object delay adjustment, but I haven't confirmed that it works just yet.
I've heard of "plug-in delay compensation" which logic has built in, but simply "recording delay compensation" is not something I'm sure exists (though it can be calculated, and varies with recording buffer size adjustments, etc), if you could please let me know how to achieve phase accurate results when recording overdub layers in software that'd be cool.
any advice would be great, thank you,
-Andrew
Old 4th March 2007
  #2
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Needlebender's Avatar
 

hey, this is my first post.... but that's exactly how I work, using all outboard into Nuendo. lots of paralell stuff

You have to calcutle the delay time in Samples.

First get an good visual wav forum, like snare. Set the snap point to Samples in your DAW. place the object onto a 1 sample snap point. (zoom way in!) write the number down in which the object is placed in the daw on the grid.

Create a track directly below that one, Then send the org track out D/A -> compressor bypassed -> A/D. Daw. into the newly created track. (start the recording on the start point of the audio object)

now zoom way in again... the new track will be slighty behind the org. now moving the new track in 1 sample incremints (agin really zoomed in to see the square samples) see how many samples you needed to move the new wav forum left, so it lines up with the org.

once its lined up, wrtie that number down, Subtrack that from your org track location number. (in samples on the grid) You should have now calculated the exact number in samples. in my system its 32 samples of delay I have to compensate for @ 44.1khz

hope that makes sence
Old 4th March 2007
  #3
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Hello,
Thank you for the clear description of your method. I'm happy to hear that Nuendo is capable of phase-accurate overdub delay compensation by simply zooming into the "sample" level and doing the alignment there. Unfortunately I'm starting to doubt that this is even possible to do in Logic5.5 (!? what ! why?), logic seems to deal with the relatively gross "ticks" and "milliseconds", but not the finer measurement of "samples". At this point I suppose I'm hoping or looking for a parameter or maybe even a plugin that would get the job done, something like that is approaching a "workaround" for something so fundamental as to be stupid. Please correct me if I'm wrong Logic Users, but it seems like the finest increments available for nudging or delaying audio events in Logic are not fine enough to account for phase - this seems ridiculous and dissapointing in a very large and small way at the same time. One tell-tale sign is that Logic doesn't let you zoom way in to the waveform level. Ableton, as far as I can remember, will zoom in all the way, though I don't know how fine the delay/nudge of the track is yet. Maybe Logic 5.5 is just limited in this way and not too many people have complained about it..it just seems so fundamental and soooo annoying, if anyone knows of another solution, please let me know, I hope I'm missing something obvious, thanks.
Old 4th March 2007
  #4
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shangoe's Avatar
 

Quote:
Originally Posted by andrewsc View Post
Hello,
Thank you for the clear description of your method. I'm happy to hear that Nuendo is capable of phase-accurate overdub delay compensation by simply zooming into the "sample" level and doing the alignment there. Unfortunately I'm starting to doubt that this is even possible to do in Logic5.5 (!? what ! why?), logic seems to deal with the relatively gross "ticks" and "milliseconds", but not the finer measurement of "samples". At this point I suppose I'm hoping or looking for a parameter or maybe even a plugin that would get the job done, something like that is approaching a "workaround" for something so fundamental as to be stupid. Please correct me if I'm wrong Logic Users, but it seems like the finest increments available for nudging or delaying audio events in Logic are not fine enough to account for phase - this seems ridiculous and dissapointing in a very large and small way at the same time. One tell-tale sign is that Logic doesn't let you zoom way in to the waveform level. Ableton, as far as I can remember, will zoom in all the way, though I don't know how fine the delay/nudge of the track is yet. Maybe Logic 5.5 is just limited in this way and not too many people have complained about it..it just seems so fundamental and soooo annoying, if anyone knows of another solution, please let me know, I hope I'm missing something obvious, thanks.


i still work with logic 5.5 and this is the way i didi it: played a shot spike-sound, (as short as you can cut it in a sample editor) DA->AD. record it on a new track. flip phase. delay the first sample only with the sample delay plugin, you will hear when it nulls out. read the amount of delay, this is what you will need on every track that never went otb->itb. on my system i use 110 samples....
Old 4th March 2007
  #5
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Ok, sample delay plugin to the rescue. That's just the sort of thing I was looking for and not remembering !! thanks thumbsup
Old 4th March 2007
  #6
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Ok, I recorded the Logic metronome which is a very short click, then recorded it again and compared using sample delay. I inverted the phase and delayed the first recording by 137 samples, the tick sound was quietest at that position. So every overdub track has a sample delay, and when making an overdub of an overdub, every non-overdubbed track has to be delayed. It seems like it'd be vastly easier to negative-delay the overdubs rather than positive-delaying all the other tracks, it seems like there needs to be a function to push audio events backwards by a number of samples. Doesn't it inevitably get difficult to manage all those delays when doing a number of overdubs? could you please clarify that procedure ? thanks!!!
Old 5th March 2007
  #7
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Needlebender's Avatar
 

In Nuendo in the recording options, there is an option for "Record offset placement" you can enter your value in samples here. Maybe logic has something similar? Any track you record will get automatically compensated for, by the amount you enter..., just have to remember to take it off when you are Not doing outboard processing.
Old 5th March 2007
  #8
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shangoe's Avatar
 

Quote:
Originally Posted by andrewsc View Post
Ok, I recorded the Logic metronome which is a very short click, then recorded it again and compared using sample delay. I inverted the phase and delayed the first recording by 137 samples, the tick sound was quietest at that position. So every overdub track has a sample delay, and when making an overdub of an overdub, every non-overdubbed track has to be delayed. It seems like it'd be vastly easier to negative-delay the overdubs rather than positive-delaying all the other tracks, it seems like there needs to be a function to push audio events backwards by a number of samples. Doesn't it inevitably get difficult to manage all those delays when doing a number of overdubs? could you please clarify that procedure ? thanks!!!
to my displeasure the delay plug do not negative delay. another workaround is to make a delay-plug on every channel in your autoload, make it on 137 samples delay by default and disable it. so you have it on every new project on every channel. when it comes to mixdown and you record a track that goes OTB->ITB you just need to set this delay to zero and enable all the other delay plugs.
Old 5th March 2007
  #9
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Hi,

It seems like putting a sample-delay plug on every track would create the problem that, when doing an overdub of an overdub, you'd then have to scoot every track yet again, adusting all those instances of the delay plugin on each track seems ridiculously untenable. Reading what you said again, I can see you're saying when recording, to effectively negative delay the track(s) going DA > AD by bypassing the delay plug for those tracks. In that case it would seem that bypassing all those delays would still amount to too much work when recording multiple tracks, since they have to be turned on and off instead of just set once, and it would involve multiple tracks more often than just negative delaying the recorded tracks. It makes sense that plugins would not be able to do a negative delay.


Here's a summary of some info I've gatherd so far :

Most programs have an adjustable preferances feature: Record Offset Placement, but Logic versions 3-6 don't have this feature , hence the problem.

(I don't really understand in what situation you'd want to disable Record Offset Placement, mentioned earlier).

Here is a webpage dedicated to the topic :
http://www.opuslocus.com/logic/record_offset.php

The most promising workaround I've heard is from that website:

"Open the recorded sample in the sample edit window
Adjust the Anchor playback position marker forward by the number of samples needed.


To move an audio region by minus X samples:
  1. Open the audio region in the Sample Editor.
  2. Ensure the Sample Editor <CODE>Edit >> Update Arrange Position</CODE> menu is unchecked.
  3. Move the region anchor point (not the region start point) to the right by X samples.
  4. Close the Sample Editor. "
The downside to this method may be slightly more mousing. I haven't tried it just yet, hopefully it really works, doens't seem all that inconvenient.

The arrange window "delay" track parameter works in ticks only, the milliseconds view is still in ticks. Ticks vary with tempo whereas samples are absolute to sample rate.

In the discussion, another aspect of latency to consider could be measuring the delay of the midi interface triggering external hardware and taking account of that as well.


Here are a few other related threads I found:
http://www.bigbluelounge.com/forums/...dcd608c8739879

this one describes a nasty sounding mLan bug, but is still relevant:
http://www.01xray.com/forums/showfla...=&fpart=1&vc=1


I'll try the new method this evening. thanks for the input,
-Andrew
Old 6th March 2007
  #10
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Hi,

I was able to try out the method of moving the Anchor point forward in the Logic 5.5 Sample Edit window by the required number of samples. Here's a good way to do it (with one point of confusion):

When you set the View Menu parameter to timeline in samples, there is a small box in the upper left corner near the timeline that displays the anchor position value in samples above what seems to be the start position. With the playback stopped, zoom in just enough so that dragging the anchor one sample at a time is easy, and just watch the anchor value until is says "-137", then let go of the anchor.

What I observe next seems to be a bug that made the test very confusing at first. When you let go of the anchor point at the desired location, the numbers representing anchor and start suddenly change to something that doesn't seem to make sense, no longer saying -137 (or even relating to the number 137 when comparing before and after). The timeline also changes position over the waveform accordingly in that way I can't understand. Anyway, the audio is still then positioned at -137 even though those values then looks rather screwed up so you have to ignore them.

This method does work if you do it right the first time. Playing around with the anchor point more than that, moving it back and forth, seemed to skew the audio in the arrange in a way along with screwing up the timeline, that made it not returnable its original position when the anchor was set back above the start point (not sure why but certainly seemed that way ). (This apparent bug made it seem like the latency was almost random until I developed a very exact and minimal procedure. Out of paranoia I also tried cycle record and rebooting and saw that the latency stayed consistent.)

The Edit menu option "update position in arrange" was unchecked, (not exactly sure what that option does yet). (Not sure how this method would even be working if the position wasn't being updated in the arrange window, it seemed to be updating there anyway..?) Snap to zero crossing was active in the edit menu as it is by default, not sure if this was affecting the timeline, but maybe it does, I'll have to check.

So that method works fairly well, but is a bit delicate if not done right. It may be a bit of a tossup which method is better, moving the anchor point, or putting a sample-delay plug on every channel and temporarily bypassing the ones on tracks playing back during the recording process. Using plugs wouldn't seem to mess up the timeline at least, but it is a slightly larger number of things to keep track of. If you're also accounting for midi latency (which I haven't really looked into yet), it might be better not to have to readjust those plugs, though you could put on a second sample-delay on each mixer channel just for midi latency assuming it stays consistent, then bypass both when needed.

thanks again,
-Andrew
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