I'm extremely pleased that the MIDI note follower is now working, including creating monophonic instruments that produce correctly-tuned pitches. This is something I've always wanted, but wasn't ever totally sure that it would work physics-wise.

Making this work required adding two new features for Modulators: (1) exponential modulation, which is required because pitch is exponential, so a linear modulation can't produce pitches from a linear midi note input, and (2) multiplicative modulation, which is required to get notes both above and below a reference note.

So to get a slide-whistle, you can hook up a MIDI Note Follower Modulator to adjust e.g. the mass of a body (you could also do spring stiffness), set it to exponential and multiplicative mode, and tune the modulation depth until it sounds right. I'm super happy not because we need more slide whistles, but because this is a good test that the MIDI Note Follower can be used for sophisticated and interesting purposes.

Now of course, the exponential and multiplicative modes work for all Modulators, and so all kinds of new things are possible outside just note following. Since Modulators can run at audio frequency, it means you can do multiplicative FM synthesis.

Here's the most basic demo of the "slide whistle" -type sound from using a note follower that's modulating the mass of several bodies based on which note is being pressed. The bow is set up to use any MIDI note as input. There's no instancing here -- what you see is the full system, and the pitch changes simply come from the modulation of the mass.

This demo gives you a sense for what kinds of weird stuff you can do by using multiplicative FM synthesis (along with some recursive modulation). What's happening is the pitch is being modulated by a sample & hold waveform in exponential, multiply mode. And the frequency of the S&H waveform is being modulated by an LFO in linear, multiply mode. I feel like it's an incredibly believable dialup modem!

One last super-simple demo of the note following, showing off a clean sound using mass modulation