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 Forum index » Clavia Nord Modular » Nord Modular G2 Discussion
Can someone help with a sequencer problem?
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ark



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PostPosted: Tue Jul 08, 2008 11:24 am    Post subject: Can someone help with a sequencer problem?
Subject description: Gate signals are just a bit too long
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Please look at (and listen to) the attached patch. The AND gate should be allowing a signal through only during a clock pulse. Therefore, this patch shows that an event sequencer module in gate mode emits an ON signal that lasts through the beginning of the next clock pulse.

This behavior makes sense, in that it allows the ON signal to be continuous if two or more adjacent indicators are turned on. However, it implies that you can't use the presence of a signal at the beginning of a note to know whether the gate is going to be on for that note.

Any suggestions for how to work around this problem?


Double pulse.pch2
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sitarman



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PostPosted: Tue Jul 08, 2008 11:37 am    Post subject: Reply with quote  Mark this post and the followings unread

I think whaqt you are hearing is an interaction between the pulse timing and the release time. I ran your patch in the demo version, when I turned the release time to zero the "echo" disappeared!
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ark



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PostPosted: Tue Jul 08, 2008 11:43 am    Post subject: Reply with quote  Mark this post and the followings unread

The echo disappeared because the envelope is quenching too quickly for you to hear it. Unfortunately, the pulse that triggers it is still there, which is a problem for the (significantly more complicated) patch that I am constructing.

The attached modification shows that it's not the envelope that's generating the double pulse, it's the fact that the gate overhangs the beginning of the next clock cycle.


Double pulse, version 2.pch2
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Blue Hell
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PostPosted: Tue Jul 08, 2008 12:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

From the help file

Quote:
T/G button

Toggle between Trig and Gate mode with these buttons. In the Trig mode, every step transmits its own logic signal, which is an exact copy of the current Clk pulse or’ed with the current state of the trigger-row chain input. In the Gate mode, the logic state of the step will be low or high for the complete duration of the step. If both the current step and the next step are a logic high the steps will be ‘glued together’ into one longer Gate signal that is actually as long as both steps.


The only way to accomplish the G mode is indeed to switch off the output on the next clock unless the following step is active as well, resulting in a double pulse in the circuit you posted.

So a solution could be to use T mode instead, but maybe with a longer positive duration of the clock signal. This could be the shape LFO for instance set to clk mode. Unfortunately thatis a bit of an expensive module, and probably you want the gluing of pulses otherwise you would not have used the gate mode, likely.

You could of course double the sequencer using one in gate mode and the other in trig mode, sequencers are relatively cheap modules to use.

Another option could be, depending on how you want to use this, to invert the output of the clock module, as that module produces short pulses that will result in a longer pulse that starts a bit late ... but there seem to be some startup issues with this? Of course the sequencer would have to be clocked by the un-inverted clock. See attached patch for this.


double_pulse_196-1.pch2
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Antimon



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PostPosted: Tue Jul 08, 2008 2:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Or maybe just use a short logic delay wherever appropriate. Not as cheap as the inverter trick perhaps.

/Stefan


double_pulse_version_2_sbt.pch2
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Antimon



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PostPosted: Tue Jul 08, 2008 2:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Antimon wrote:
Or maybe just use a short logic delay wherever appropriate. Not as cheap as the inverter trick perhaps.

/Stefan


By the way, I tried using a mixer to delay the signal with one sample, but that didn't work (maybe the G2 compiler was too clever for that). Could some other simple module be used for a miniscule delay?

/Stefan

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PostPosted: Tue Jul 08, 2008 2:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, another variation ...


double_pulse_version_2_sbt_174-1.pch2
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ark



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PostPosted: Tue Jul 08, 2008 2:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Right. The thing is, though that if I set two adjacent cells in the sequencer, I want them to run together into a single gate.

Let me elaborate on what I'm trying to do. Ultimately, I would like to write a fairly flexible sequencer that I can use in live performance. The idea would be to use the front panel knobs and switches to enter the notes and their durations.

So the idea is to have a note sequencer (actually more than one so that I'm not limited to 16 notes) together with an event sequencer. Each gate cell in the note sequencer turns on a note; the corresponding cell in the event sequencer makes the note longer.

Right now, I have divided each 16th note into three equal segments, hence 48th notes. If just the note sequencer itself is turned on, the note is 2/48ths long; if the note sequencer is off and the event sequencer is on, then the note is 1/48th long. Finally, if both of them are on, the note takes up the full 16th note.

This is pretty easy to do so far. Where I am running into trouble is that I want to allow for notes longer than 1/16th. I am doing that with the following rule: If two consecutive steps in the sequencer have the same pitch, and the first of those steps has both sequencers turned on, then the second note is considered part of the first note. Similarly for subsequent notes.

You may ask why I care whether another note starts when the pitch changes. The reason is that I want to restart the amplitude envelope in that case, or if I'm using MIDI, I want to send another MIDI note off/on pair. So I put together a little note-change detector with a sample-and-hold module, two level comparison modules, and a gate.

So far, this has been difficult enough that I'd rather try to untangle what I have a little before posting it.
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ark



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PostPosted: Tue Jul 08, 2008 2:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK, I've attached my current version. It is definitely too complicated, but at least should give an idea of what I'm trying to do. Right now what definitely doesn't work as I would like is that the two consecutive identical notes should be tied together--but more generally, I think there must be a simpler way of doing this.


Sequencer test.pch2
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Blue Hell
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PostPosted: Tue Jul 08, 2008 4:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

To complicated for me now - bed time really Wink

Was toying a bit myself and made attached, not sure if it's anything like you'd want - the control interface is different.


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PostPosted: Tue Jul 08, 2008 4:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'll have a look tomorrow, when my brain isn't fried.

I do know that I want to keep note sequencers in there. Ultimately I'm thinking about having more than one, with clock dividers to select between them (i.e. use sequencer #1 most of the time, but use #2 for every measure that's a multiple of 4, and #3 for every measure that's a multiple of 12, overriding #2).

The idea is to be able to enter a melody one note at a time through the front-panel dials, then save it as part of the preset. Maybe even use it as a bass line with the keyboard selecting the root and a pitch quantizer to force it to a given key.

Right now, though, the attached photo describes how I feel.


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ark



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PostPosted: Wed Jul 09, 2008 4:21 pm    Post subject:
Subject description: Almost working now
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The patch is almost doing what I want, except that it is sustaining the note too long at the end of each repetition. I think that what is happening is that when there is a pause followed by the same note as before, the note isn't getting restarted properly.

From experience I know that the way to solve a problem like this is to avoid looking at it for a while and come back to it with fresh eyes. More tomorrow...


Sequencer 2008-07-09.pch2
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PostPosted: Thu Jul 10, 2008 11:19 am    Post subject:
Subject description: OK, I think I have it now...
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I have to say that I learned a lot working on this patch.

The idea is that the selector boxes in the note sequencer represent a 24th note, and the selector boxes in the event sequencer add a 48th note to that. So if they're both on, you get an entire 16th note.

Here are some of the problems I encountered.

First, if I have two consecutive 16th notes, I want to end the first note and start a second if and only if the pitch changes. So I needed to detect pitch changes.

On the other hand, I do not want to change the pitch of the note being played during a rest. So I also have to remember the pitch commanded by the sequencer until the next note starts.

It should be possible to replace the oscillator/envelope/output modules by a MIDI send module and use this sequencer to control an external device or another Slot.


Sequencer 2008-07-10.pch2
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