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A probability drummer is an instrument that decides whether or not to trigger a sample based on a probability that can be tuned per step. I love using these things as VSTs on my computer, one was included in the venerable Buzz for Windows, they're great, Caustic doesn't have one.
What I have here is really hacky, requires 3 instruments plus two per extra channel of probability, and only modulates the volume of an instrument instead of triggering samples itself. However, you can decide with what probability you will hear an instrument per note, basically using velocity as a numerical percentage chance, and that's just cool.
With all that out of the way, let's get to explaining what's going on here:
Hat Src is playing straight 16ths on a hi hat. Its volume is turned down.
Neg is outputting a purely negative voltage. It has to be a PCMSynth because AFAIK, that's the only instrument that won't immediately cancel out the voltage by pushing it to zero. If anyone has a way of making a negative voltage easily in Modular, that would make this a lot cleaner.
Hat Prob is the actual probability engine we'll be focusing on. Signal flow starts upper left, then goes down and wraps to the the right, roughly.
We take Hat Src and wire it to the output, we'll use the built in volume mod to turn the hat on and off. Fun fact, this would be quite a bit easier if this volume mod interpreted a negative voltage to mean it should turn off the signal. Instead it actually inverts the signal, which is wacky.
So first we take a noise module and find a way to control the probability it lands above or below zero. Here I'm using note velocity to push it up, and our handy dandy PCMSynth to pull it down.
Throw these into a mixer and tune their volumes so that, at full velocity, the noise is just barely all above zero, and at low velocity, it's just below zero.
Since we want the volume to be either completely on or completely off, We'll put the output through a saturator on max. This doesn't do a perfect job. I kind of like it like that, but you can put it through another saturator at this point if you want. This is where the first oscilloscope is in my patch.
Now we put the signal into a sample and hold with a very short decay going to its gate, so that the volume changes on every note instead of all the time.
Since the volume mod needs the signal to be at zero to turn off, we need to push our signal up so that the lowest it goes is zero. Here I'm using a DADSR to do that, (something you can blame paulovski for,) because when you mix the output and inverted output of the the DADSR, you get a constantly positive voltage.
We already have a negative voltage being piped in from the PCMSynth, and we could totally use that to pull the signal down instead of up, and save 3 Modular slots in the process, but then the lowest velocity would give the highest probability of being heard, and that's just silly.
So anyway, we mix the DADSR outputs together, then mix that with our carefully crafted signal, remembering to adjust its volume properly, and we have our probability gate! Finally we put an AR ENV on the final mixer's mod, because we don't want it playing when there's no note being played, and hook it up to the synth's volume mod.
There! We made a rough facsimile of a probability drummer that takes a bunch of CPU and only modulates the volume of one channel! Is there anything we can't make with Caustic? Will I spend three hours explaining every patch I make? Is there a character limit on this forum? I guess we'll never know.