This is the first stage of the pitch to voltage converter for my Shakuhachi 2 Synth project. The incoming signal from the microphone is bandpass filtered and a pulse train is derived from the signal. This is possible because the signal/waveform of the Shakuhachi is nearly sinusoidal. At least in the higher register. As you can see on the screenshot.

Shakuhachi 2 Synth Procect: Shakuhachi signal Ro kan

In the lower register you need to adjust you playing a bit. Not in pitch but in timbre. Playing a honking RO otsu will confuse the circuitry. It is hard to discriminate between the basic pitch and the overtones in the analog domain. This can be partly corrected setting a high threshold in the filter.

Shakuhachi 2 Synth Procect: Shakuhachi signal Ro otsu

First stage if the filter is 36dB high pass followed by a 36dB low pass. They form a bandpass with the frequency adjusted to a 1.8 Shakuhachi. The filter is followed by a comparator and a differentiating circuit. After some level shifting we get a pulse train at the output with the same pitch as the sinusoidal input signal. The output is 5V and around 150 micro seconds.

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse schematic

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse stuffed PCB

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse Faceplate