Pitch to voltage converter

Pitch to voltage converter: Front view
Pitch to voltage converter: Front view

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).

Specs and features

  • Software driven pitch to voltage converter
  • 12bit resolution
  • V/Oct output
  • Offset CV Fine and coarse adjustment
  • Runs on +/-15V and +/-12V
  • Power consumption around 45mA positive rail, 15mA negative rail

The documentation and the Gerber files for download can be found in my website.

Pitch to voltage converter: Microprocessor board
Pitch to voltage converter: Microprocessor board
Pitch to voltage converter: Control board
Pitch to voltage converter: Control board

The incoming pulse train is feed to the microprocessor. IC1 (301-F) prevents the microprocessor from negative inputs. Zener D2 prevents from overvoltage. The trigger starts an internal timer of the microprocessor in input capture interrupt mode. The ticks are counted and the count is then looked up in a table. The lookup table provides the values for the V/Oct conversion. The read value is the send to the DAC MCP4921 which is follwed by a low pass (IC1A, 301-B)). IC2A (301-F) adds the offset voltage and IC2B (301-F) corrects the phase.

Pitch to Voltage converter: Populated PCB's
Pitch to Voltage converter: Populated PCB’s
Pitch to Voltage converter: Side view
Pitch to Voltage converter: Side view

Compressor with optional pedal steering

Compressor: Font view
Compressor: Font view

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.

Specs and features

  • Compression rate and gain adjustable by hand or/and foot pedals
  • Audio path not affected when no compression is used
  • Runs on +/-12V and +/-15V (with minor resistor value changes for best performance)
  • Power consumption below 20mA each rail

The documentation and the Gerber files for download can be found in my website.

Compressor: Schematic
Compressor: Schematic

When the ratio is set to zero and the gain to one the input signal passes through the circuitry unaffected (IC2C, IC2A IC6OTA1, IC6OTA2, IC2D). When the compression rate is turned up a DC voltage is derived from the input signal wit a precision full wave rectifier and some filtering (IC1A, IC1B, IC1C, IC1D). This voltage is used to open the VCA in the side chain (IC3OTA1, IC3OTA2, IC2B). The signal from the side chain is then subtracted from the main signal (R13, IC2A). The now compressed signal is then potentially amplified (IC6OTA1, IC6OTA2)

Compressor: Populated PCB
Compressor: Populated PCB
Compressor: Back view
Compressor: Back view
Compressor: Front with pedal connector
Compressor: Front with pedal connector

Foot switch connector

Foot swithc connector: Front view
Foot swithc connector: Front view

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.

Specs and features

  • Four independent switches
  • Signal flow stays intact when foot switch removed
  • Runs on +/-15V and +/-12V
  • Power consumption below 10mA each rail

The documentation and the Gerber files for download can be found in my website.

Foot switch connector;: Schematic
Foot switch connector;: Schematic

The switch in the DG202 is hold in on position with a 100k resistor against the positive rail. With a foot switch attached you can pull down the hold voltage when you close the foot switch.

Foot switch connector: side view
Foot switch connector: side view
Foot switch connector: Back view
Foot switch connector: Back view

Signal to Trigger Converter

Signal to Trigger Converter: Front view
Signal to Trigger Converter: Front view

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.

Specs and features

  • Two added inputs
  • Threshold manually and with CV
  • Output for +Trig, -Trig and +/-Trig: 0.1msec
  • Runs on +/-15V and +/-12V with minor resistor changes
  • Power consumption below 25mA each rail

The documentation and the Gerber files for download can be found in my website.

Signal to Trigger Converter: Schematic control board
Signal to Trigger Converter: Schematic control board
Signal to Trigger Converter: Schematic main board
Signal to Trigger Converter: Schematic main board
Summed signal to trigger
Summed signal to trigger

The incoming signals are summed up. Every time when the summed signal changes polarity (moving through zero) a trigger is generated. Moving from plus to minus generates a trigger at the negative trigger output, moving from minus to plus generates a trigger at the positive trigger output. Trigger length is about 0.1msec.

Screenshot sine to trigger
Screenshot sine to trigger

The uppermost line (Yellow) shows the input signal. The second line (Blue) shows the trigger when the input signal moves to the positive site. The third line (Purple) shows the trigger when the input signal moves to the negative site. On the fourth line (Green) you can see both triggers added. This picture is taken without any threshold.

Signal to Trigger converter: Back view
Signal to Trigger converter: Back view
Signal to Trigger converter: Side view
Signal to Trigger converter: Side view

Limiter / Compresssor

Limiter / Compressor front view

Limiter / Compressor front view

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.

Specs and features
• Switch compress or limit
• Switch Compression/Limit rate 50% or 90%
• Compression/Limit rate adjustable 0–max
• Runs on +/-15V and +/-12V (with minor resistor changes)
• Power consumption below 15mA each rail

The documentation for download can be found in my website.

Limiter / Compressor schematic 01

Limiter / Compressor schematic 01

The audio signal flows unaffected through IC1A/B. When the compressor – limiter kicks in the inverted signal is added (=subtracted) at the summing node of IC1A. The signal level to subtract is regulated through a Sims VCA. The CV generation for the VCA is pretty standard. Linear for the compressor and exponential for the limiter.

Limiter / Compressor schematic 02

Limiter / Compressor schematic 02

Precision full wave rectifier with filter to generate the control voltage for the VCA from the audio signal.

Limiter / Compressor populated PCB

Limiter / Compressor populated PCB

Limiter / Compressor back view

Limiter / Compressor back view

Shakuhachi 2 Synth Project: E-Shak Interface

Shakuhachi 2 Synth Project: E-Shak Interface

Shakuhachi 2 Synth Project: E-Shak Interface

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.

Shakuhachi 2 Synth Project: E-Shak Interface schematic

Shakuhachi 2 Synth Project: E-Shak Interface schematic

The voltage from the accelerometer is buffered and level shifted in the first operational amplifier. The amplification of the second stage is adjustable so you can spread the signal range. The inputs from the touch sensitive switches are buffered and signaled with LED.

Shakuhachi 2 Synth Project: E-Shak Interface stuffed PCB

Shakuhachi 2 Synth Project: E-Shak Interface stuffed PCB

Shakuhachi 2 Synth Project: E-Shak Interface back view

Shakuhachi 2 Synth Project: E-Shak Interface back view

Shakuhachi 2 Synth Project: E-Shak Interface side view

Shakuhachi 2 Synth Project: E-Shak Interface side view

S2S Project: Pitch 2 Voltage Converter

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.

 

Pitch 2 voltage converter: schematic

Pitch 2 voltage converter: schematic

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

Pitch 2 voltage converter: timing diagram

Pitch 2 voltage converter: timing diagram

A clock of about 320kHz is used to drive a 12bit binary counter. The outputs of which are fed through latches and then to a 12-bit DA converter. The voltage is then converted to V/Oct characteristic with a anti-log generator. The additional circuitry is to control the timing sequence, gating the clock signal and generating a flag signal. The flag is generated when the outputs of the counter all reach a high level. This condition is reached when the input is removed or the input frequency drops below the systems lower frequency limit.

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

Pitch 2 voltage converter: stuffed PCB

Pitch 2 voltage converter: stuffed PCB

Pitch 2 voltage converter: Front

Pitch 2 voltage converter: Front

Pitch 2 voltage converter: Back

Pitch 2 voltage converter: Back

Shakuhachi 2 Synth Project: Shak 2 pulse

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

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

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 schematic

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse stuffed PCB

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse stuffed PCB

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse Faceplate

Shakuhachi 2 Synth Project: Shakuhachi 2 pulse Faceplate

Shakuhachi 2 Synth Project: Brief project outline.

I have build my first synthesizer in the late 70’s. And I am playing Shakuhachi for seven 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 with playing the shakuhachi, without affecting the playability of the flute.

So far it consists of three main modules: the pitch-to-voltage converter, the envelope follower and the “E-Shak”. 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.

Shakuhachi 2 Synth project: Block diagram

Shakuhachi 2 Synth project: Block diagram

In the block diagram you can see the basic structure of the project. The microphone signal goes to the “Shak 2 Pulse” converter and the envelope follower (ENV). The Shak 2 Pulse converter is a band pass filter followed by a zero crossing detection with adjustable threshold. The output is a pulse train with the same frequency (pitch). This pulse train is converted to a voltage according to the pitch. The output voltage is available in V/Hz and V/Oct format. 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.

Shakuhachi 2 Synth project: stuffed flight case

Shakuhachi 2 Synth project: stuffed flight case