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 Forum index » Clavia Nord Modular » G2 Building Blocks
A Classic VCO Style Multi-waveform Oscillator Bank
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varice



Joined: Dec 29, 2004
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PostPosted: Mon Jan 30, 2012 8:48 pm    Post subject: A Classic VCO Style Multi-waveform Oscillator Bank
Subject description: CEM3340 VCO IC style oscillator building block
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[EDIT: Unless you want the triangle-to-sawtooth waveform shape morphing of this patch, use the “CEM Osc Bank b” patch posted below instead. It is more DSP efficient and CEM3340 waveform phase accurate.]

Here is a classic style multi-waveform oscillator bank building block patch.

The G2 system does not have a phase locked multi-waveform oscillator module like the classic Curtis Electro Music VCO IC chips used in the famous Prophet-5 rev3 and many other analog synths. The OscDual module is a step in the right direction, but it is not the same. (BTW, is the OscDual modeled after an oscillator bank used in another synth?)

The CEM VCO IC chip produces simultaneous phase locked triangle, sawtooth and square/pulse waveforms that when mixed/crossfaded together produce unique waveforms that otherwise cannot be produced by any single G2 oscillator module or consistently by a mix of free running oscillators.

This oscillator bank patch requires a gate signal to sync the waveform phase of the three oscillator modules. Normally this sync is only needed one time after the patch is loaded or the optional pulse phase offset control is changed. The G2 digital oscillators will remain in locked phase thereafter (as long as the patch is not reset by another slot patch load or by an Editor change, etc.) In fact, a continuous hard sync on every wave cycle is not recommended, because unfortunately, the G2 oscillators produce a lot more digital aliasing noise when synced on every cycle. In this demo patch a mono keyboard gate is used to provide a sync gate one time for each new note played. A poly keyboard module would be required for polyphonic patches, of course.

An optional ultra fine linear frequency detune for the bank is provided. A control level is patched into the linear FM input of each oscillator in the bank. Each oscillator FM modulation amount should be set the same, typically a value of 1. This is highly recommended for use in detuning the bank versus other banks or oscillators. This type of detune occurs naturally in analog synths.

Note that there is an optional triangle-to-sawtooth waveform morph shaper control and a pulse wave phase offset control adjustment provided that are not normally available with typical CEM VCO IC chip synth designs. The value of the pulse phase offset control level must be greater than -64 and less than +64 to work properly, and the bank will need a new sync gate to update the pulse phase after the offset value is changed. Note that if you do not use this offset control, you can delete the second sample and hold module, but then you must connect the output of the first sample and hold to the sync input of the pulse oscillator.

Variation 1 is a mix of triangle and sawtooth waves that produces the unique “shark tooth” waveform of the Moog Minimoog Model D synth.

Variation 2 is an equal mix of triangle and square wave.

Variation 3 is an equal mix of triangle and square wave with the optional pulse phase offset value set to +32, which shifts the phase of the fundamental frequency of the square wave to be in phase with the fundamental frequency of the triangle. This gives the strongest fundamental mix of these two waves. The resulting waveform makes a great one to be used for powerful bass and mellower lead patches but still with plenty of harmonics.

Variation 4 is an equal mix of triangle and square wave with the optional pulse phase offset value set to -32, which shifts the phase of the fundamental frequency of the square wave to be 180 degrees out of phase with the fundamental frequency of the triangle. The resulting waveform has a high amount of harmonics in relation to the fundamental, great for edgy and aggressive sounding patches.

This type of bank is used as a three oscillator bank in the patch “mm 3 Osc VM” posted here:

http://electro-music.com/forum/topic-9258.html

In the case of the “mm 3 Osc VM” patch, the three oscillator waveforms in each bank are mixed through two crossfaders. The bank pitch is controlled by an octave range switch and a continuously adjustable -7 to +7 semitone control (similar to the Minimoog Model D oscillator controls).

EDIT: corrected instruction on how to connect the sync signal to the pulse osc if the optional pulse phase offset control is not used.


CEM Osc Bank.pch2
 Description:
CEM VCO IC style oscillator building block patch

Download
 Filename:  CEM Osc Bank.pch2
 Filesize:  3.92 KB
 Downloaded:  423 Time(s)


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varice

Last edited by varice on Sat Feb 25, 2012 8:18 pm; edited 2 times in total
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varice



Joined: Dec 29, 2004
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Location: Northeastern shore of Toledo Bend
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G2 patch files: 49

PostPosted: Mon Jan 30, 2012 9:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here are some waveform scope captures.


Variation 4 triangle+square -32 phase offset waveform.JPG
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 Viewed:  150 Time(s)
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Variation 4 triangle+square -32 phase offset waveform.JPG



Variation 3 triange+square +32 phase offset waveform.JPG
 Description:
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Variation 3 triange+square +32 phase offset waveform.JPG



Variation 2 triangle+square waveform.JPG
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Variation 2 triangle+square waveform.JPG



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varice
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varice



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PostPosted: Mon Jan 30, 2012 9:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

And one more scope capture.


Variation 1 Shark Tooth waveform.JPG
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Variation 1 Shark Tooth waveform.JPG



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drapdap



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PostPosted: Tue Jan 31, 2012 4:15 am    Post subject: Reply with quote  Mark this post and the followings unread

nice work Varice!

i will check this tonight, thanks!
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iPassenger



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PostPosted: Tue Jan 31, 2012 4:47 am    Post subject: Re: A Classic VCO Style Multi-waveform Oscillator Bank
Subject description: CEM VCO IC style oscillator building block
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Thanks for posting the description sounds very interesting. Smile

varice wrote:

In this demo patch a mono keyboard gate is used to provide a sync gate one time for each new note played. A poly keyboard module would be required for polyphonic patches, of course.


One thought though, can this not create clicks when a new note is played whilst the last one decays?

The poor handling of the sync, caused by the precise tuning jitter and sampling frequency is the thing that annoys me the most about the G2 but it is constrained by it sampling frequency I guess.

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varice



Joined: Dec 29, 2004
Posts: 719
Location: Northeastern shore of Toledo Bend
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G2 patch files: 49

PostPosted: Tue Jan 31, 2012 11:03 am    Post subject: Re: A Classic VCO Style Multi-waveform Oscillator Bank
Subject description: CEM VCO IC style oscillator building block
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Thanks for the comments guys.

iPassenger wrote:
Thanks for posting the description sounds very interesting. Smile

varice wrote:

In this demo patch a mono keyboard gate is used to provide a sync gate one time for each new note played. A poly keyboard module would be required for polyphonic patches, of course.


One thought though, can this not create clicks when a new note is played whilst the last one decays?...

Actually no, it will not. This sync method using a S&H module is a neat trick. I should have explained it in more detail in the OP. The high gate signal “arms” the S&H which then waits until the signal from the reference oscillator (in this case, the sawtooth osc) makes a negative to positive zero cross. Only then does the S&H output go high to supply the sync signal to the other oscillators. The sync only occurs at the right point in the reference wave cycle, not at the instant that the high gate occurs. The reference oscillator is free running and not synched at any time. The G2 oscillators do track pitch very accurately, so if they are all supplied with the same pitch signal, the waveforms will stay in phase. Since there is no sudden phase change, no click or glitch can be heard. I hope that I explained it well enough. Feel free to ask for clarification if not.

I learned this S&H sync trick from FlowerP here:

http://electro-music.com/forum/viewtopic.php?highlight=sync+shot&t=27421

iPassenger wrote:
...The poor handling of the sync, caused by the precise tuning jitter and sampling frequency is the thing that annoys me the most about the G2 but it is constrained by it sampling frequency I guess.

Yep, the excessive sync noise from the G2 oscillators is very annoying. But that may just be the nature of digital VA. But it seems that Clavia could have done better. Maybe the idea proposed here by Tim would work better:

http://electro-music.com/forum/topic-17606.html

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PostPosted: Tue Jan 31, 2012 12:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ahh sorry i hadn't looked at the Patch. I have a vague memory of this trick and it sounds very smartpy applied. Lookng forward to spending some time with this patch.
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PostPosted: Tue Jan 31, 2012 1:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, no problem Ross! Very Happy Your concern is legitimate, since its too easy to really foul up a patch with an improper sync scheme. Sad
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PostPosted: Wed Feb 01, 2012 1:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice work! Really great waveforms are possible.
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PostPosted: Wed Feb 01, 2012 7:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Ross! I'm glad that you like it.
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dorremifasol



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PostPosted: Tue Feb 07, 2012 2:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice! with an additional LFO and a sub-oscillator it would make a cool sounding monosynth ^^
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varice



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PostPosted: Tue Feb 07, 2012 10:58 am    Post subject: Reply with quote  Mark this post and the followings unread

dorremifasol wrote:
Nice! with an additional LFO and a sub-oscillator it would make a cool sounding monosynth ^^

Very Happy

Actually, I started with the “mm 2 Osc VM” monosynth patch from here and stripped it down to make this building block patch. Wink

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varice



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PostPosted: Sat Feb 25, 2012 8:09 pm    Post subject: Re: A Classic VCO Style Multi-waveform Oscillator Bank
Subject description: CEM VCO IC style oscillator building block
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Here is a “CEM Osc Bank b” building bock patch that is much more DSP load efficient and more waveform phase accurate in reference to the CEM3340 VCO IC chip output of my Prophet 5 rev3.3 synth. Unless you want the triangle-to-sawtooth waveform shape morphing of the patch posted above, this one should be used instead.

In addition to the controls in the first patch, this patch has a T Phase offset control which can be used to adjust the phase of the Triangle waveform relative to the Sawtooth and Pulse. The normal setting to match the CEM3340 triangle phase is +32. Values other than +32 will produce unique waveforms when mixing/cossfading the Triangle wave with the Sawtooth and/or Pulse waves. The value of this phase offset control level must be greater than -64 and less than +64 to work properly.

This patch also has a P LConv control used to adjust the level and phase of the Pulse waveform. The normal setting to match the CEM3340 pulse is BipInv.

varice wrote:
...Variation 3 is an equal mix of triangle and square wave with the optional pulse phase offset value set to +32, which shifts the phase of the fundamental frequency of the square wave to be in phase with the fundamental frequency of the triangle. This gives the strongest fundamental mix of these two waves. The resulting waveform makes a great one to be used for powerful bass and mellower lead patches but still with plenty of harmonics.

Variation 4 is an equal mix of triangle and square wave with the optional pulse phase offset value set to -32, which shifts the phase of the fundamental frequency of the square wave to be 180 degrees out of phase with the fundamental frequency of the triangle. The resulting waveform has a high amount of harmonics in relation to the fundamental, great for edgy and aggressive sounding patches...

Note that with the default settings of the T Phase offset value at +32 and the P LConv control set to BipInv, the setting of the optional P Phase offset control will result in differences between this patch and the first. A value to -32 will put the fundamental frequency of the Square and Triangle waveforms in phase. A value of +32 will put them out of phase.

I had used an OscShpB module for the Triangle oscillator in an attempt to correct an earlier waveform phase error in my “mono monster VM” patch, but with further testing, this turned out to be a mistake (complicated by the fact that the 1.40 OS G2 and G2 Demo Software oscillators do NOT sync to the same point of the waveform Evil or Very Mad This of course means that the G2 Demo will not reproduce these CEM patches correctly Rolling Eyes ). Fortunately, the default settings of both patches *sound* the same when loaded into a 1.40 G2 synth, even though the Triangle waveform of the first patch is 180 degrees out of phase Exclamation

EDIT: A new “mono monster VM” patch based on this building block is posted here:

http://electro-music.com/forum/topic-9258.html


CEM Osc Bank b.pch2
 Description:
A more DSP efficient CEM3340 version

Download
 Filename:  CEM Osc Bank b.pch2
 Filesize:  4.11 KB
 Downloaded:  379 Time(s)


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Last edited by varice on Mon Feb 27, 2012 4:46 pm; edited 1 time in total
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dorremifasol



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PostPosted: Sun Feb 26, 2012 3:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you! Sounds great and it's very fun to tweak this patch! Smile

I noticed the filter envelope being bipolar, is this correct? doesn't seem to work as it should.

What is a pity is the G2 sounding so dull on the low frequencies. The triangle wave doesn't have the kind of sound you would expect from an analog synth.

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PostPosted: Sun Feb 26, 2012 2:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

I’m glad that you like this patch, Albert.

I like the filter EG bipolar mode output. Once you have set the filter cutoff at the EG sustain level (which is zero in bipolar mode), you can tweak the EG and envelope amount all you want without affecting the cutoff at sustain. When using the more common positive unipolar mode, tweaking the EG or amount can mess up the cutoff at sustain, which usually means that you have to tweak the filter cutoff again. It takes a little bit to get used to how the EG works in bipolar mode. I should have assigned that parameter to the front panel though so that the mode could be easily switched.

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PostPosted: Sun Feb 26, 2012 3:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

varice wrote:
...I should have assigned that parameter to the front panel though so that the mode could be easily switched.


Laughing I just noticed that you can switch the output mode by pushing the button under the EG Shape knob.

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