Shakuhachi 2 Synth project. Shak 2 Pulse

Motivation

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.

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.

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.

Specs and features

Input Shakuhachi 1.8 signal
Output pulsetrain 5V/~150micro seconds. Same pitch as input
Adjustable threshold
Runs on +/-15V and +/-12V (with minor resistor value changes)
Schematic Shakuhachi 2 pulse filter
Pictures
Download docs

Implementation

Schematic

Description:

First stage if the filter is 36dB Sallen-Key high pass followed by a 36dB Sallen-Key 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.