Motivation

I have build my first synthesizer in the late 70’s. And I am playing Shakuhachi for several years now. Time to bring both worlds together. Here we go.

The aim of this project is to provide Shakuhachi players with the means to control an (analogue) synthesizer simultaneously while playing the Shakuhachi, without affecting the playability of the flute.

So far the core consists of three main modules: the pitch-to-voltage converter, the envelope follower and the “E-Shak”. With some supporting modules around them. The pitch-to-voltage converter derives a voltage from the pitch played on the Shakuhachi. This is used primarily to control the pitch of the VCO (which is the initial generator of waves in the synthesizer). The envelope follower provides a voltage which follows the volume of the Shakuhachi, together with gate and trigger signals. These are used mainly in conjunction with the synthesizer’s VCA (which is responsible for the dynamics of the synthesizer’s signal). The “E-Shak” is an exoskeleton attached to the Shakuhachi with crepe tape. It is equipped with an accelerometer with three axes and with three switches. This module provides three control voltages according to the movement of the Shakuhachi, and three additional on/off switches. The usage is only limited by the player’s imagination.

The main problem is to detect the frequency in the lower octave (otsu) when the player adds overtones (second harmonics). If the volume off the second harmonic rises about a certain point the pitch to voltage detection is screwed up. To avoid this the Shakuhachi player has to take care of his playing stile. It is hard to come by this problem technically because the second harmonic in the lower register (otsu) equals the pitch in the higher register (kan). I have taken some countermeasures against this, but in the analogue world it can not completely resolved. In the moment I have a good working all analog system (except the pitch to voltage converter) which tracks the pitch very well when the player gets used to it and handles the overtones with some care. I have gone through a lot of configurations and optimizations of the modules. I can think of a few more improvements in the analog world, but it is coming to an end. Maybe the digital world is the next logical step. I can think of programming a DSP or such. I am a bit hesitant though. I know I can do it, but I'd love to stay in the analog world.



Shakuhachi 2 Synth project: Block diagram

Shakuhachi 2 Synth project: Block diagram

In the block diagram you can see the basic structure and patch of the project. The microphone signal goes to the microphone pre-amplifier. The output is then low-pass filtered to dampen the second harmonic. The low-pass helps with feedback loops as well. The signal is then compressed to take care of the wide dynamic range of the Shakuhachi. The compressor ratio and gain is steerable with pedals to be adaptable to various playing styles of the player without taken the hand from the flute. The signal to trigger module generate a pulse train which is feed in the pitch to voltage converter. The output of the pitch to voltage converter is a V/Oct voltage according to the pitch of the Shakuhachi. The V/Oct voltage can be offset to fit the needs of the following VCO (not on the picture).

The signal for the envelope follower is taken from behind the low-pass filter. The envelope follower generates the gate (+5V), the trigger (+5V/20ms) and a voltage following the amplitude of the microphone signal.

The “E-Shak” is an exoskeleton equipped with a three axis accelerometer and three touch sensitive switches. With the interface you can adjust the gain and the inclination of the accelerometer signal. It provides three gate signal (+5V) as well.

Picture is outdated

S2S Current state

Used modules

Not all modules are specifically build for the Shak 2 Synth project. I use already available modules for the patch where ever possible.

Microphone Preamplifier

Microphone preamplifier

Microphone Preamplifier

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Current state: Version 1.1.0 published

I needed a microphone preamplifier for my Shakuhachi 2 Synth project. So i build one. The schematic follows the circuitry given in the data sheet of the SSM2019. Nothing fancy. A optional volume indicator is added. I didn't bother with phantom power. I already have a external unit and didn't want to go into the trouble designing something.

24dB low pass filter

Fixed 24dB low pass filter

24dB low pass filter

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Current state: Version 0.9.0 published

This is a 24dB low pass filter with fixed frequency. The given part values are dimensioned for the Shakuhachi flute to dampen the second harmonic slightly. It also prevents feedback from the microphone. The cut off frequency and filter response is easily adapted to your needs by changing part values. Details can be found in "Acitve Filte Cookbook" second edition by Don Lancaster pg. 142.

Open points:

Which cut off frequency should be used for best performance?

Compressor with optional pedal steering

Compressor with optional pedal steering

Compressor with optional pedal steering

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Current state: Version 0.9.9 published

This is the revised version of my Limiter/Compressor. First built for my Shakuhachi to Synth project to handle the great dynamic range of the Shakuhachi. Here I left out the limiter and added a make up amplifier. The structure used is derived from "Small Signal Audio Design", second edition by Douglas Self p682ff. The audio signal did not flow through a VCA as in many other implementations. Instead the compression is done by subtracting the audio signal at the output summing node according to the control voltage derived from the audio signal. The compression rate and the make up gain is adjusted by hand or/and optionally with foot pedals. The foot pedals are an additional option particularly made for wind players. It works without this option in your setup as well.

Signal to Trigger converter

Signal to Trigger converter

Signal to Trigger converter

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Current state: Published

This module was originally build for my Shakuhachi to Synth project to provide the start/stop pulse for the Pitch to voltage converter. But it turned out to be much more useful. When you have the basics for your synthesizer like VCO, VCF, VCA, ADSR, LFO,... and some controllers and you want more, then using your keyboard to steer the synthesizer it is time for some modules to produce trigger signals out of different sources. Here is one of them. A signal to trigger converter. You can feed in a changing signal and every time the signal went through zero a trigger is generated dependent on the direction from where the zero point is crossed. You can add a threshold manually or CV controlled to move the zero point up or down as well. You can feed the signal in through input one ore two. When both inputs are used the signals are added together. When the signal crosses zero from positive to negative a trigger of about 0.1msec is generated at output -Trig. When the signal crosses zero from negative to positive a trigger of about 0.1msec is generated at output +Trig. Output +/-Trig provides both triggers. This output can be used to generate interesting rhythmic patterns when the threshold is set by a slowly moving CV or some DC offset is applied to the signal.

Pitch to voltage converter

Pitch to voltage converter

Pitch to voltage converter

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Current state: Version 3.0.1 published

This is the software driven replacement for my all hardware pitch to voltage converter from my Shakuhachi to Synth project. The software driven approach has the advantage of easily adaption for different frequency ranges. In my case it is the range of the Shakuhachi. To change the range just adapt the software. It is completely temperature independent. The needed input is a pulse train derived from your original signal. You can use my Signal to Trigger converter to provide the pulse train. An offset voltage is added to the V/Oct output to fit the needs of your VCO (Synthesizer).

Envelope follower

Envelope Follower

Envelope follower

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Current state: Version 1.1.0 published

This envelope follower was first build for my Shakuhachi 2 Synth project. But it is useful for any other input signal which you want to derive a control voltage from. It provides a gate and a trigger signal as well. The envelope follower is used to detect the amplitude variations of the incoming signal and produces a control voltage that resembles the variations in the input signal. The gate and trigger signal is derived from the input signal as well. You can vary the threshold to determine at what minimum signal level the gate goes high and the trigger fires. Gate level is +5V. Trigger level is +5V/1msec.

E-Shack Interface

E-Shack Interface

E-Shack Interface

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Current state: Version 0.9.5 --- Next: Version 1.0.1 To be published

Here is the interface for my "E-Shak". The input comes from an exoskeleton attached to a Shakuhachi. It is connected to the interface with a 10 wire ribbon cable. The exoskeleton is used as addition to the pitch 2 voltage converter and the ENV follower. Inputs are three voltages from a three axis accelerometer (x, y, z) and three touch sensitive switches (Gate 1, 2, 3). The output range foe x, y, z is adjustable in gain and volume. This gives a wide variability in usage. The three gates are 5 V. The state is indicated with LED.

Foot switch connector

Foot switch connector

Foot switch connector

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Current state: Version 0.9.0 published

As a Shakuhachi player I need my hands on the flute. So I use me feet to manipulate parameters and switches on the synthesizer. This module was originally build for my Shakuhachi to Synth project to provide the possibility to connect foot switches with the synthesizer and keep the patch intact when they are removed. The signal is not routed through the foot switch. Instead CMOS switches are used, turned on and off with the foot switch. So the signal stays within the synthesizer and the connection to the foot switch carries only DC. Removing the foot switch does not interrupt the signal flow in the synthesizer.

Pedal/CV Send and Receive

Pedal/CV Send and Receive

Pedal/CV Send and Receive

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Current state: Version 1.0.1 published

As a wind player I need to keep my hands on the wind instrument. This module was first thought for connecting pedals to my modular for changing control voltages. But it is useful to include external signal changers like echo or delay or any other sound and CV source as well. It has no signal amplification or attenuation though. For audio use I recommend using my Audio Send and Receive module.

Obsolete/Replaced - Kept for reference

Limiter/Compressor

Limiter Compressor

Limiter/Compressor

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Current state: Version 1.1.0 published (replaced)

To handle the great dynamic range of the Shakuhachi I needed a compressor for my Shakuhachi 2 Synth project. Because a limiter is not that different I added this feature as well. This comes in handy with my Vocoder project also. The structure used here is derived from "Small Signal Audio Design" by Douglas Self p682ff. The audio signal did not flow through a VCA as in many other implementations. Instead the compression or limitation is done by subtracting the audio signal at the output summing node according to the control voltage derived from the audio signal.

Shak to pulse filter

Shakuhachi 2 pulse filter

Shak 2 Pulse filter

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Current state: Version 1.0.1 published (replaced)

This is the front end to the pitch 2 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.

Pitch to voltage converter

Pitch to Voltage converter

Pitch 2 Voltage converter

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Current state: Version 1.2.0 published. (replaced)

Here is the pitch 2 voltage converter for my Shakuhachi 2 Synth project. It is based on an article in Electronotes EN#84 p5-p9 from Robert Iodice. It consist of some control logic and a 12bit DA converter. I have found a fault in the control logic and simplified the DA converter. The original only had a V/Hz output, so I added a V/Oct output..

The circuitry takes a pulse train and converts it to a voltage according to the frequency of the pulse train.

The circuit has the advantage of sampling very quickly (only two pulses required) and holding indefinitely.

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