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 Forum index » Clavia Nord Modular » Bugs
[G2 1.40] Constant Module
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gurk



Joined: May 27, 2004
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PostPosted: Fri Sep 08, 2006 4:45 pm    Post subject: [G2 1.40] Constant Module
Subject description: constant bug?
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There seems to be a bug in the constant module.

The constant's value jumps from 62 to 64 in bipolar mode.

When the constant is set to 64, the module's output isn't exactly 64.

If you use a constant module to tune an oscillator set to -64 back to 0 semitones, and mix it with an oscillator set at 0 semitones instead of getting a 2 x amplitude signal it produces a slow beating effect which suggests that output is not exactly 64.

Here is a patch which demonstrates this.

g


constant module bug.pch2
 Description:
patch to demonstrate constant module error

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 Filename:  constant module bug.pch2
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mosc
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PostPosted: Fri Sep 08, 2006 4:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, this looks like a bug to me too. Funny nobody ever noticed such a problem before...
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jamos



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PostPosted: Fri Sep 08, 2006 6:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've seen that too, but it makes.. some sense.

Since the G2's opprams are stored as 7-bit values, they only have 128 different values. This could be 0 to 127, or -64 to +63. Apparently they hacked around this limitation by replacing +63 with +64.
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varice



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PostPosted: Fri Sep 08, 2006 9:23 pm    Post subject: Re: [G2 1.40] Constant Module
Subject description: constant bug?
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gurk wrote:
There seems to be a bug in the constant module.

The constant's value jumps from 62 to 64 in bipolar mode.

When the constant is set to 64, the module's output isn't exactly 64.

If you use a constant module to tune an oscillator set to -64 back to 0 semitones, and mix it with an oscillator set at 0 semitones instead of getting a 2 x amplitude signal it produces a slow beating effect which suggests that output is not exactly 64.

Here is a patch which demonstrates this.

g


Regarding the possible error with the Constant module +64 value output - my testing indicates that instead there appears to be a problem with the way the oscillators respond to a +64 value control signal. The oscillators respond the same way to logic high values - which should also equal +64 units. The CompSig module also shows that the Constant +64 value output and logic high output values are equal.

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gurk



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PostPosted: Mon Sep 11, 2006 6:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Regarding the possible error with the Constant module +64 value output - my testing indicates that instead there appears to be a problem with the way the oscillators respond to a +64 value control signal. The oscillators respond the same way to logic high values - which should also equal +64 units. The CompSig module also shows that the Constant +64 value output and logic high output values are equal.


Good idea, I never thought of testing that!

For what its worth, i tested my patch on the G2 demo software and found that the beating/phase effect was a different speed (much faster) from running it on my G2 Engine.

If you change the octave shift on the patch you get different beating speeds (only able to check this on the demo at moment).

I wonder if this is some kind of rounding error?
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sebber



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PostPosted: Mon Sep 11, 2006 7:39 am    Post subject: Reply with quote  Mark this post and the followings unread

It's got to do with the 127 MIDI numbers, it's Clavia's solution for it. I remember having read about this. If I'm right t's been in the old NM workshop on Clavia's website, there's a workshop about how the NM deals with numbers in general.
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sebber



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PostPosted: Mon Sep 11, 2006 7:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Relation between knob positions and units

Any knob can be set to one of 128 positions. This exactly matches the MIDI specification, where e.g. a CC signal, or a note number with its velocity value, can have values from 0 up to 127. As MIDI CC’s are used to control the position of knobs on synths, how does the knobsetting or a CC value, if it’s assigned to a knob, relate to the effect that setting has in a module? Do some experimenting with knobs with different control curves until you fully understand what’s happening.

Note that some knobs that control a value between –64 and 64 miss the value of 63. Test this with a Constant module. If the Uni button is depressed the value of 63 is missing and if the Uni button is pressed the value of 63,5 is missing. This is as there are only 128 possible positions, between –64 and 64 are 127 integer values, adding –64 and 64 to this collection of values would mean 129 knobpositions. But MIDI has only 128 possible knobpositions and so have the module's knobs. Rescaling the –64 up to 64 range to 128 equal values would mean that all values except the –64 and 64 would become fractional numbers and 0 would disappear from the collection. As the value of 0 and 64 are so important (total silence or unity gain), Clavia chose to simply skip the 63 value and use 64 in it’s place. This also means that a knobsetting of 127 must actually be considered a setting of 128 instead of 127 if that knob has a linear behaviour!

To summarise:

It’s not the physical position of the knobs that defines what happens if we scale down an ON state of 64 units but the underlying system that couples the knob position with the arithmetic value to be used in the calculation.
It is important to only use knobs with linear behaviour if we want to have a predictable result. That's why there’s that Lin button on the ControlMixer module. The knobsetting 64 (and not 63) on the control mixer will exactly halve the signal, but the knobsetting 127 will mean unity gain, so although the arithmetic is linear the relation between the knob’s physical position and the underlying arithmetic is slightly irregular, compensating for a small deficiency in the MIDI specification.


http://www.clavia.se/nordmodular/Modularzone/LogicIntro.html

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mosc
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PostPosted: Mon Sep 11, 2006 9:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Sigh - the low res nobs are the weakest link in the Nord Modulars, IMHO. It just takes a minute playing an Alesis ION to see the value of higer resolution knobs.
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ian-s



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PostPosted: Mon Sep 11, 2006 11:47 am    Post subject: Reply with quote  Mark this post and the followings unread

mosc wrote:
the low res nobs are the weakest link in the Nord Modulars


Agree 100% (or 99.5%)
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gurk



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PostPosted: Mon Sep 11, 2006 2:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok this explains the jump from 62 to 64. Shocked (good OLD 8bit)

What about the movement in the sound as if the two synced oscillators are not perfectly in tune when you mix them together ? (as demonstrated in my patch)

In my opinion (which has changed a bit since reading Varice's post) there must be something going wrong with pitch modulation input when it receives a value of +64, hence the beating effect. Surely this is not part of the design?

I've also found that the beating effect in my patch has a different speed on G2 hardware than when run on the G2 demo software, this suggests to me that they are being tuned differently, this shouldn't be right, should it?

If you try my patch and change the octave shift on both demo and hardware, with the patch attached at the top of the page, you should hear a differing modulation speed between hardware and software.

cheers,
Graeme

Last edited by gurk on Thu Sep 14, 2006 4:49 pm; edited 2 times in total
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mosc
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PostPosted: Mon Sep 11, 2006 2:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

g2ian wrote:
mosc wrote:
the low res nobs are the weakest link in the Nord Modulars


Agree 100% (or 99.5%)


Maybe you mean, "99.21875%" That's, 127/128 Twisted Evil

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dasz



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PostPosted: Tue Sep 26, 2006 8:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Code:
Sigh - the low res nobs are the weakest link in the Nord Modulars, IMHO. It just takes a minute playing an Alesis ION to see the value of higer resolution knobs.


Yup yup yup. I keep getting some zipping in some patches with very minute knob movements -- just today as a matter of fact, I was altering my DYI resonance circuit, and it kept zippering. Introducing a little bit more delay in the feedback loop, eliminated the zipper.

Won't apply here, I'm afraid.
/Dasz

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