Octave down

[Ben N]

All it is at its heart is a compressor running in to a state variable filter that tracks the incoming signal by comparing the response from the high pass and low pass through rectifiers and an integrator and then the low pass filter is fed in to a comparator to get the square that gets a gate fed from the compressors rectifier to stop it running wild at the tail end of the note.

Is that all? 

You're right... it would definitely be better if the signal was split in to 6 copies that were band passed filtered

It's complicated and high parts count in the analogue realm but that's why I thought it would make a good stand alone digital chip because it is a great fundamental extractor, not my scope picture (credit goes to processaurus) but here it is turning a square wave input in to a sine:

That does look like it would be a significant step forward leap forward for any number of DIY projects, at the cost of a PIC or an Arduino-type microcontroller and a few lines of code. And yes, why not six bands?