Motivation

Shakuhachi 2 Pulse filter

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


Implementation

Schematic

Shakuhachi 2 Pulse filter schematic

Shakuhachi 2 Pulse filter 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.


Shakuhachi 2 Pulse kan register

Shakuhachi signal in RO kan


Shakuhachi 2 Pulse otsu register

Shakuhachi signal in RO otsu

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Calibration

  • Apply a sine to the input. Adjust TR1 and TR2 so that the filters are not overdriven. The adjustment is not critical.

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Special parts

None

Download

S2S: Shak 2 pulse documentation download


Shakuhachi 2 Pulse stuffed PCB

Shakuhachi 2 Pulse filer: Stuffed PCB


Shakuhachi to Pulse filter Front

Shakuhachi 2 Pulse filter: Frontview


Shakuhachi to Pulse filter Back

Shakuhachi 2 Pulse filter: Backview


2017 Mai

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