Predator: problem with delay causing pitchmodulation when shifting tempo in sequencer

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jappe
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Post 29 Jan 2015

Hello,

I'm using the Predator a lot; extraordinary RE with a high density of perfect patches.
Today I stumbled into a problem I don't really understand, perhaps it's a defect?

Scenario:

1. Set the sequencer tempo to 70bpm
2. Insert a Predator, select the "Lead - Berliner Schule" patch.
3. Record a couple bars of notes for the Predator track, beginning from bar #2.
4. Insert a tempo shift track to 100bpm, with the same duration
5. Start playing from bar 1.

==> The Lead sound echo gets pitch modulated because of the tempo change even though the tempo change and note happens at the same time.
If I turn of the Echo on the Predator, then the problem is gone.


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eusti
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Post 29 Jan 2015


Yes, happens here as well.
Weird.

Happens until the tempo shift is half a bar earlier here...
D.

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Olivier
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Post 29 Jan 2015

As far as i understand your example, i think there are more delay units that exhibit this behaviour. Some units compensate for time changes, others don't.
The ECHO changes pitch, unless you enable "keep pitch".
The echo algorithm on the RV700 doesn't.
The DDL-1 does.
Synchronous doesn't... but has a Keep pitch button like the ECHO.. The keep pitch only applies to internal time changes. On external time changes (tempo) the pitch stays the same..
So i guess its all down to the behaviour of the echo unit. Some do, some dont. Or am i missing the point here ? :)

So if you want an echo, and a time change, but no changes in pitch, you have options ;)
:reason: V9 | i7 5930 | Motu 828 MK3 | Win 10

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jappe
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Post 29 Jan 2015

Thank's all!
@eauhm:  I have verified that the same behavior goes for a subtractor and a DDL1.
@eusti: Also verified that setting the tempo a bit before note start makes it work.

I guess I'll just automate the delay off for a couple ticks as a workaround.
It's unclear to me why it happens though. I mean, if I change the tempo while there is a note on, then I'd expect the pitch change. But there is no note before.

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Benedict
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Post 30 Jan 2015

It is because a DDL (and all software delays are really DDL) is really a row of samples set to play back at the 'root' pitch which is defined by the current tempo and delay time. Each sample is recorded now and played back later at now+n samples (n defined by tempo/delay time). When tempo changes the samples still get played back in order but the timing is different so they play faster or slower and change pitch. e.g.:

If tempo is 60bpm and the Delay is 2/16ths, samples are recorded expecting to play back with those settings. When tempo is moved to 120bpm the samples will suddenly play back at twice the speed so the pitch will rise by one octave. Exactly the same will occur if you leave the tempo at 60bpm but change the Delay time to 1/16th. Those samples "in the pipe" will play back in order but at twice the speed.

At the point of a sudden change you will tend to hear a "spang" sound as the pitch changes. Smoother changes are less noticeable and will give a nice chorusing sound (which is exactly what a chorus is). Buttons that "keep pitch" will play maths games with the sample playback to minimize the artifacts (whilst introducing others).

:)

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jappe
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Post 30 Jan 2015

Benedict wrote:It is because a DDL (and all software delays are really DDL) is really a row of samples set to play back at the 'root' pitch which is defined by the current tempo and delay time. Each sample is recorded now and played back later at now+n samples (n defined by tempo/delay time). When tempo changes the samples still get played back in order but the timing is different so they play faster or slower and change pitch. e.g.:

If tempo is 60bpm and the Delay is 2/16ths, samples are recorded expecting to play back with those settings. When tempo is moved to 120bpm the samples will suddenly play back at twice the speed so the pitch will rise by one octave. Exactly the same will occur if you leave the tempo at 60bpm but change the Delay time to 1/16th. Those samples "in the pipe" will play back in order but at twice the speed.

At the point of a sudden change you will tend to hear a "spang" sound as the pitch changes. Smoother changes are less noticeable and will give a nice chorusing sound (which is exactly what a chorus is). Buttons that "keep pitch" will play maths games with the sample playback to minimize the artifacts (whilst introducing others).

:)
Hi, thank's for the explanation.

Hmm...need to investigate this...unsure what's going on.

EDIT: Ok so It actually seems like something is wrong. I do like this:

1. Set default tempo to 70 
2. setup a subtractor with default patch chain a DDL-1 to it.
3. Make a few C-notes only, in bar 2.
4. Automate the tempo to 100 exactly when the first subtractor note hits.
5. Play it from bar 1.

Expected result: I get the C-notes, and no pitch change since I do not change tempo during the sequence of notes.
Actual result: Pitch modulated notes for the echo just as I would have expected if the tempo was changed while playing the first note - Which I don't do.

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