1/3 and 2/3 filter keyboard tracking

[HansH]

HI,

Does someone has a simple technique to get 1/3 or 2/3 keyboard tracking right on the sub37? I want to explore some minimoog like techniques on the sub37, but getting the filter tracking right is a bit tricky.

Cheers,
HansH

[stiiiiiiive]

[EDIT: as pointed out later on by oli@sub37 (thanks ) this is not correct. Please refer to the next couple posts.]

Basically, when kb tracking equals 1, that means that the filter cutoff frequency follows exactly the keyboard voltage, hence allowing to play resonance as note. Start by setting max resonance and set the cutoff frequency at a decent, audible value when playing the leftmost C key for example.
At KB tracking = 1, you will need to play the next C key to have the resonance peak increased by one octave.
At KB tracking = 2/3, you will need to play the second next C key to have the resonance peak increased by one octave. To find that setting, play alternatively the first and the third C keys adjusting the KB tracking untill the two resulting resonance peaks are separated by one octave.
To find the setting KB tracking = 1/3, repeat with the first and fourth C key.

Hope it helps

[HansH]

Thanks for your response. The challenge is though that changing the KB tracking also changes the cut off frequency. I am unfortunately not blessed with perfect pitch hearing so I need to add an oscillator for pitch reference and correct both cut off frequency and KB track to find the right range.
Fortunately the Moog engineers did a terrific job with the KB track settings: the ratio is nearly perfect linear in the whole knob range: I measured the self oscillating frequency of the filter for the lowest an the highest C on the keyboard for the whole range of the KB track (using the Sub37 Mac editor and the tuner in Ableton to measure the frequencies). For those interested the measurements and the regression fit

As the fit is near perfect it is easy to calculate the 1/3 and 2/3 tracking :

1/3 : 2731
2/3: 5461


Cheers,

Hansh

[oli@sub37]

At KB tracking = 2/3, you will need to play the second next C key to have the resonance peak increased by one octave. To find that setting, play alternatively the first and the third C keys adjusting the KB tracking untill the two resulting resonance peaks are separated by one octave.

Great idea do get a certain desired ratio for the KB tracking! But wouldn't what you describe result in a 1/2 KB tracking?
My understanding of 2/3 KB tracking is that you need to increase the key by 3 octaves to get 2 octaves of pitch increase. So you would have to play the fourth C to get the double octave from the first key. I think.

[stiiiiiiive]

I am wrong indeed, but I think you are too

My understanding of 2/3 KB tracking is that you need to increase the key by 3 octaves to get 2 octaves of pitch increase.

Right.

So you would have to play the fourth C to get the double octave from the first key.

Actually not: the double octave is just one octave higher. We are talking about the quadruple octave here.

To double check that: as a 1V increase in pitch leads to a 0.66V increase in filter cutoff, you'll need to increase 3V in pitch to fall on 2V increase in filter frequency. That is: a note 3 octaves higher leads to a filter frequency 2 octaves higher.
So it's more like: you'll have to play the fourth C to get a frequency 2 octaves higher than the first key, i.e. not the double but the quadruple octave.

Consequenly, for 1/3 tracking, playing the fourth C will lead to a frequency 1 octave higher, which is the double octave now. Makes sense since the 1/3 tracking is half as much as the 2/3 tracking.

BTW this is simpler to do with the 3 octave keyrange Sub37 than with a Sub Phatty hehe.

Thanks for pointing out that error. I mentioned that in my former post

[HansH]

The 1/3 tracking is quite cool, it can add some delightful dirt to the sound: try this

- Init sound
- Oscillator 1 Saw 50% volume
- Keyboard tracking 1/3
- Raise resonance just before self resonance
- Play notes and turn cut off

to make it more nasty : try 6dB filter , or turn up feedback

[stiiiiiiive]

(1 pole filter is not Model D compliant )

[oli@sub37]

So it's more like: you'll have to play the fourth C to get a frequency 2 octaves higher than the first key [...]

Which is exactly what I said:

So you would have to play the fourth C to get the double octave from the first key.

IOW: With 2/3 KB tracking you have to play the fourth C (triple (!) octave) to get the sound of the third C (double octave). Or somesuch...

[stiiiiiiive]

Problem is either I'm not an english native speaker (totally possible cause) or we are using words "double octave" in the wrong way. Confusing.

I understood your "double octave from the first key" as "twice the frequency of the note played when depressing the first key". That's where I must have been wrong.

I'm trying to make myself clear now :
When you depress the first C key, you get a pitch frequency 'P' and a filter cutoff frequency 'fc'.
2/3 tracking means that:
When depressing the 4th C key, you get a C three octaves above (i.e. resulting in a pitch equal to 8P) and the resulting filter cutoff frequency will be 2 octaves above fc (that is, equals to 4fc).



..Ok we seem to agree indeed

[oli@sub37]

Problem is either I'm not an english native speaker (totally possible cause) [...]

Me neither...

..Ok we seem to agree indeed

Great!

BTW, thanks again for pointing out that it's possible to use keys/octaves to get ratios for the tracking. Altough the concept is obvious, it didn't occur to me when I was trying to acheive an exact 2/3 KB tracking on my Sub37 ...

[stiiiiiiive]

I’m glad it helped