Drift bug

[fizzy]

Hello Jeff! The Drift function working only for track 1, track 2-8 doesn't works if track 1 in reset mode.
Also I can't change the "Drift Resync Frames" less 513, but 513 is too coarse for my ears. I'd like to have this variable around 100. Please...

My setup: Windows XP, Mobius 2.1 Ableton Live 8.2.2
Thank you.
Dmitry

[Jeff]

Are all the tracks using the same sync source? What sync source is it?

Drift isn't a function I expected people to use, I use it in a few test scripts but it was supposed to be hidden. It will bring the track back into alignment which whatever sync source it is using. In practice this only applies to tracks that use MIDI In, MIDI Out, or Host sync.

The problem with setting Drift Resync Frames too low is that there is usually quite a bit of jitter especially with MIDI clocks. The drift tends to balance over time, for example the first pass of a loop may drift -185, then the second pass will be 69, then the third -118, then 112, then -42, etc. So the average drift is relatively low but the swings up and down on each loop pass can be much higher than 100. In my testing with MIDI I usually see them in the -256 to 256 range.

If you set Drift Resync Frames too low, then you will be doing a drift correction on almost every pass of the loop. Several people did this and then complained about hearing the "crossfade bump" at the start of ever loop.

If you are using Host sync the amount of drift is typically smaller so we could lower it for that. MIDI Out sync has jitter about the same as MIDI In but a little better.

[fizzy]

Originally Posted by Jeff

Are all the tracks using the same sync source? What sync source is it?

Yes all the tracks using the same sync source (HOST). Mobius working as VST Plugin into Ableton 8.2.2 Also the parameter "MIDI/Host sync unit" = BAR

Originally Posted by Jeff

Drift isn't a function I expected people to use, I use it in a few test scripts but it was supposed to be hidden.

Yes of course, I'm understand it, but please don't hide it, because it's really important feature for the precision rhytmic music when using as HOST Sync.

Originally Posted by Jeff

It will bring the track back into alignment which whatever sync source it is using. In practice this only applies to tracks that use MIDI In, MIDI Out, or Host sync.

As for MIDI you are absolutely right, but for HOST Sync 513 and more it's too coarse. In my test the Drift=513 it's around 1/32 note, it's too coarse for rhytmic music and of course not problem for ambent styles.

Originally Posted by Jeff

The problem with setting Drift Resync Frames too low is that there is usually quite a bit of jitter especially with MIDI clocks. The drift tends to balance over time, for example the first pass of a loop may drift -185, then the second pass will be 69, then the third -118, then 112, then -42, etc. So the average drift is relatively low but the swings up and down on each loop pass can be much higher than 100. In my testing with MIDI I usually see them in the -256 to 256 range.

And again with MIDI you are absolutely right, but with HOST Sync it's a big question...

Originally Posted by Jeff

If you set Drift Resync Frames too low, then you will be doing a drift correction on almost every pass of the loop. Several people did this and then complained about hearing the "crossfade bump" at the start of ever loop.

If you are using Host sync the amount of drift is typically smaller so we could lower it for that. MIDI Out sync has jitter about the same as MIDI In but a little better.

As for my test it will be great precision around Drift=100-200 if I use Mobius as VST Plugin with HOST Sync! Please...

[Jeff]

I'll lower the limit, but I'd like to know more about what you are hearing.

At 44100 frames per second, a 512 frame drift is around 11.6 milliseconds.

At 120 BPM a 1/32 note is around 62 milliseconds.

A delay less than 20ms is usually heard as "flanging", to be heard as "doubling" it has to be above 20ms.

So if you are hearing an obvious doubling or flamming effect, there may be something else going on here besides drift.

[fizzy]

Originally Posted by Jeff

I'll lower the limit, but I'd like to know more about what you are hearing.

Thank you so much!

Originally Posted by Jeff

At 44100 frames per second, a 512 frame drift is around 11.6 milliseconds.

At 120 BPM a 1/32 note is around 62 milliseconds.

A delay less than 20ms is usually heard as "flanging", to be heard as "doubling" it has to be above 20ms.

So if you are hearing an obvious doubling or flamming effect, there may be something else going on here besides drift.

Here is link for mp3 file with drift correction 512 frames and log file DBWin32
http://ge.tt/6WhQ5jH/v/0?c

00:00 playing loop from Ableton slot
00:09 playing loop from Ableton slot and Mobius track with same loop
02:53 drift 100 frames
05:26 drift 200 frames
08:13 drift 300 frames
11:00 drift 400 frames
14:00 drift 500 frames
14:16 drift resync on 512 frames

Also dont forget about problem with Drift in 2-8 tracks please (IMHO it's more critical problem in SYNC engine)

[Jeff]

You did this before didn't you? :-)

It sounds like you have a drum pattern playing in the host, then you record that and let the host and the loop play at the same time. This is a great way to test sync because even the slightest amount of phase shift will be audible. It sounds about like I was expecting, each pass of the loop puts it one more sample out of phase and you can hear the timbre changes, it's sort of like a "step flanger" with no modulation. By the time it got to 512 it still didn't sound like doubling to me, more like a very slight chorus effect.

I agree we should let people lower the threshold but if you had recorded a different signal, say a guitar track rather than the drum pattern, it would have been much, much harder to hear and I doubt most people would notice.

I'll fix this and Drift 2-8 in the next release.

Oh, and this does point out an annoying problem I've seen in several hosts. They aren't always accurate about telling the plugin where the beat or bar is so in this case the Mobius loop ends up 1 frame longer than the host loop. This seems to be tempo related. At some tempos it is perfect and there is never any drift, at others it will be off by 1 or 2 and the loops very slowly drift apart.

For this case, I'm thinking Mobius should detect this and just shorten the loop by one frame. If we see we're drifting by 1 on every pass we can correct that early and you would never reach the threshold.

[fizzy]

Originally Posted by Jeff

You did this before didn't you? :-)

It sounds like you have a drum pattern playing in the host, then you record that and let the host and the loop play at the same time. This is a great way to test sync because even the slightest amount of phase shift will be audible. It sounds about like I was expecting, each pass of the loop puts it one more sample out of phase and you can hear the timbre changes, it's sort of like a "step flanger" with no modulation. By the time it got to 512 it still didn't sound like doubling to me, more like a very slight chorus effect.

I agree we should let people lower the threshold but if you had recorded a different signal, say a guitar track rather than the drum pattern, it would have been much, much harder to hear and I doubt most people would notice.

I agreed with you absolutely! As for guitar sound it's not problem, but for drums it's a bit annoying. I'll happy if you lower the threshold for drift.

Originally Posted by Jeff

I'll fix this and Drift 2-8 in the next release.

Great! I'm waiting the next release...

Originally Posted by Jeff

Oh, and this does point out an annoying problem I've seen in several hosts. They aren't always accurate about telling the plugin where the beat or bar is so in this case the Mobius loop ends up 1 frame longer than the host loop. This seems to be tempo related. At some tempos it is perfect and there is never any drift, at others it will be off by 1 or 2 and the loops very slowly drift apart.

For this case, I'm thinking Mobius should detect this and just shorten the loop by one frame. If we see we're drifting by 1 on every pass we can correct that early and you would never reach the threshold.

As always you are absolutely right! It's great idea! I understand what you mean, because I made some small loopers in Max/MSP and I have all these problems too :-)