Fun with key follow and the mod matrix?

  • Noticed something that (to me) seems odd, while trying to figure out a way to avoid FM in Wave mode from drastically changing the quality of the sound across note ranges (i.e. modulates at faster rate for higher notes).

    Set Osc Balance so only one Oscillator is audible (to make this more obvious). Then put that Oscillator's Key Follow to 0. Experimenting while holding a note when changing from 32 to 0 Key Follow, you will notice that lower notes increase in pitch and higher notes decrease - it seems some C in the middle is used a base pitch or something. I'm assuming this is what leads to the odd behavior that follows.

    With Key Follow set to 0, go to the Mod Matrix and set Slot 1's source to Key Follow, and its Destination to the Oscillator's pitch. Set amount to 32, notice that the Oscillator's pitch matches what it normally does with its own Key Follow at 32.
    Set Slot 1's amount to 0, and set Slot 2's Destination to Slot 1 amount. Set Slot 2's amount to 32. Notice that low notes now effectively play backwards (edit: while high notes continue to ascend almost normally, though they cap out early).

    Not entirely certain why this happens. I don't suppose anybody has any thoughts on making use of this behavior?

  • Actually, it's the same logic that helps create the curved attack slope. What you experience is "squaring" (as in x²) the key follow value. Note that x² is always positive. In the Virus, middle C is considered 0 for key following. C# above middle C is considered 1. B below middle C is considered -1. 1² = (-1)², and the mirroring behavior goes on all across the keyboard.
    You can use this to alter the perceived shape of any modulation source, such as LFO. In the case of the attack mentioned above, you get a parabolic attack curve, which is different from the exponential curve a modular analog synth RC circuit will give you, but it's close enough.
    Happy tweaking!

  • Thanks for the answer and suggestions, flabberbob. I was actually hoping for an answer with such an explanation, so that is really appreciated.

    Extrapolating from your explanation, I tried a little test attempting "cubing" of key follow.
    My expectation was that middle C would remain middle C, the B below remain the B below, but the A# below would be equal to the E below, as (-2)^3 would be -8.
    I am comparing Osc 1 with modified key follow with Osc 2 with normal key follow; it could just be that my hearing is off, but it doesn't sound to me as if this is what happens, so I am again puzzled.
    It sounds more as if the pitch difference between notes is greatly lessened, many notes sounding almost the same pitch even.

    If you happen to understand what is going on in this situation, I would be happy to have an explanation for this. I don't quite understand what is going on with this, but I think if I did, I could probably make some use of this type of thing.

  • Thanks for the reply.
    Here is the patch setup:

    Osc 1 key follow: 0

    Slot 2 and 3 source are Key Follow.

    Slot 2 Destination 1: Osc 1 pitch, amount 0

    Slot 3 Destination 1: Slot 2 Destination 1, amount 0
    Slot 3 Destination 2: Slot 3 Destination 1, amount 32

    Regarding the saturation described, can you tell me if there is a usual result of this? For instance, if saturation were reached when attempting to control pitch, would I notice all note pitches being the same?
    Would they be at some extreme point (very high or very low pitches)? Just curious, as while I think I understand how this can be an issue, I'm not sure what troubles it causes or how one would recognize it occurring.

  • I have recreated you routings with the only difference that all of mine sit in slot 1. I have noticed the "floor" and "ceiling" pitches, in the "square function" as well as in the "cube function", its just that since the 3rd power is more "acute" than the 2nd power, the floor/ceiling is reached earlier. The reason for it is probably the saturation effect of the limit Access has put on the amount an oscillator's pitch can be shifted.
    Now, this is where my answer turns into a BUG REPORT. While in the key-follow[osc1pitch=0,slot1dest1=32] routing all worked as expected, in the key-follow[osc1pitch=0,slot1dest1=0,slot1dest2=32] mode, notes played at the same time (polyphonic patch) had mutually affected each other, to sound like an FM/AM (ring mod) effect, and also the order of notes added influenced the result. I used a sine oscillator to make it easy on my ears, but other waveforms are equally distorted. At some point, many pressed notes sound like a fax transmission. I did all this on a desktop running OS4.5.3 in standalone, so should be easy to reproduce. Access people, if you're reading this, reply here if you need more details. I'm wondering of this is reproducible in TIOS5.

  • I happen to be using OS 5, actually; probably should have mentioned it before, but I didn't think of it.
    I believe I followed your repro steps correctly, as I was able to notice this effect as well.
    I had:
    Osc 1 key follow at 0
    Slot 1 Dest. 1 -> Osc. 1 pitch, amount 0
    Slot 1 Dest 2 -> Slot 1 Dest 1, amount 0
    Slot 1 Dest 3 -> Slot 2 Dest 2, amount 32

    I kind of enjoy the effect, but I have the feeling most people would not.

  • I have also verified that this can be worked around by using a different slot, e.g. slot 2 amount 1 to do the work of slot 1 amount 3. BUT THEN I noticed something else - when you set the sound to mono and increase the portamento (glide), upon adding the second note, the glide starts from a different pitch, thus breaking the expected continuity.
    I'm wondering if an official bug report was opened for this.