/digital-synth-vra8-u

Monophonic/Paraphonic United Synthesizer with Chorus FX for Arduino Uno

Primary LanguageCCreative Commons Zero v1.0 UniversalCC0-1.0

Digital Synth VRA8-U v2.2.8

Concept

  • Monophonic/Paraphonic United Synthesizer for Arduino UNO R3
    • Monophonic Mode: 1-Voice, 2-Oscillator (with Sub Oscillator)
    • Paraphonic Mode: 4-Voice, 1-Oscillator
    • Built-in Chorus FX
    • Controlled by MIDI: VRA8-U is MIDI Sound Module
  • The 8th in the Digital Synth VRA8 series that pushes the limits of the Arduino UNO R3

Caution about Arduino AVR Boards Version

  • We strongly recommend Arduino AVR Boards version 1.8.5 (or from 1.8.3 to 1.8.6)
    • If you use another version, the sketch may not work well: CPU Busy LED (LED L) may continue to be lit

Change History

  • v2.2.8 (2024-02-04):
    • Fix display of VRA8-U type-16 CTRL
  • v2.2.7 (2024-02-04):
    • Easier to customize control numbers
  • v2.2.6 (2023-08-17):
    • Fix behavior when Portamento is 0 (Off)
  • v2.2.5:
    • Fix Pulse Wave (Fix problem with small Saw Wave sound heard)
  • v2.2.4:
    • Fix Filter Key Track (Fix problem with strange sound when pitch is outside of note number range)
    • Change Program Change #0-7 by CC to Program Change #8-15 by CC
  • v2.2.3:
    • Fix Osc 2 frequency in Monophonic Mode
  • v2.2.2:
    • Separate Voice Mode Lgt (Legato) into Lgt (Legato) and LP (Legato Portamento)
    • Fix Voice Mode value 32 to be Mon (Monophonic) mode
  • v2.1.0:
    • Make the VRA8-U main unit recognize Program Change #8-15 (It is valid when VRA8-U CTRL is not used)
    • Improve stability
  • v2.0.0:
    • Add support for VRA8-U type-16 (Special Edition with 16-bit Audio Output)
    • Modify Preset #3 and #5
  • v1.4.0:
    • Add the parameter "Chorus Bypass [Off|On]"
  • v1.3.0:
    • Rename the parameter "Osc 1 Shape II" to "Osc 1 Morph";
    • Remove SS (Shaped Saw Wave) from Osc 1 Wave, and change the behaviour of Osc 1 Morph for Pls (Pulse Wave);
    • Change the texts "EG Osc Dst [P|P2|S1]" and "LFO Osc Dst [P|P2|S1]" to "EG Osc Dst [P|2P|1S]" and "LFO Osc Dst [P|2P|1S]";
    • Change to reflect the Filter Cutoff parameter smoothly;
    • Improve stability (Reduce CPU busy time when receiving Note ON in paraphonic mode);
    • Fix a bug where the effect of LFO Osc Amt was inverted when LFO Osc Dst is 1S (Osc 1 Shape);
    • Fix a bug in which changing MIDI In * with VRA8-U CTRL did not invalidate the setting before the change;
    • Change to recommend Arduino AVR Boards version 1.8.5 (or 1.8.3);
    • Support Arduino Nano (ATmega328) with restrictions;
    • Add Recommended Circuit Diagram and Actual Wiring Diagram;
    • Rename "Parameter List" to "Parameter Guide"; Improve documentation; Other changes
  • v1.2.1: Reverses the effect of the Osc 1 Shape II value for SS (Shaped Saw Wave)
  • v1.2.0: Change the range of Osc 1 Shape from -64 -- +63 to 0 -- 127; Fix the comment on Osc 1 Shape II in VRA8-U CTRL
  • v1.1.1: Reduce noise in Chorus Mode M and S2
  • v1.1.0: Add SS (Shaped Saw Wave) to Osc 1 Wave; Add Osc 1 Shape II; Reduce noise when Chorus Delay Time changes; Improve Random Ctrl of VRA-8 CTRL not to change Amp Level; Improve notes for $$ and $$$; Other changes
  • v1.0.1: Reduce noise when Osc 1 Shape changes; Fix Parameter List

Features

  • Serial MIDI In (38.4 kbps)
    • We recommend Hairless MIDI<->Serial Bridge to connect PC
    • NOTE: A combination of a MIDI Shield (or MIDI Breakout) and a power supply adapter is better to avoiding USB noise
      • To use MIDI Shield (or MIDI Breakout), take #define SERIAL_SPEED (31250) (31.25 kbps) in "DigitalSynthVRA8U.ino"
      • Even using only the power supply adapter significantly reduces USB noise
  • PWM Audio Out (Unipolar, Line Level) L/Mono: Pin D5 (or D6), R: Pin D11
    • Sampling Rate: 31.25 kHz, PWM Rate: 62.5 kHz, Bit Depth: 8 bit
    • NOTE: When using the SparkFun MIDI Shield (DEV-12898), it should be modified to #define L_MONO_AUDIO_OUT_PIN (6) in "DigitalSynthVRA8U.ino"
    • We recommend adding RC filter (post LPF) circuits to reduce PWM ripples
      • A 1st-order LPF with a cutoff frequency 7.2 kHz (R = 220 ohm, C = 100 nF) works well
    • We recommend adding AC coupling capacitors to reduce DC components
      • A 10 uF electrolytic capacitor works well
  • Files
    • "DigitalSynthVRA8U.ino" is a sketch for Arduino UNO R3 (ATmega328P)
    • "make-sample-wav-file.cc" is for Debugging on PC
      • Requiring GCC (g++) or other
      • "make-sample-wav-file-cc.bat" makes a sample WAV file (working on Windows)
    • "generate-*.rb" generates source files
      • Requiring a Ruby execution environment
  • VRA8-U type-16

Limitations

  • Waveforms may slightly distort when receiving MIDI bytes continuously
    • At that time, CPU Busy LED (LED L) probably blink
    • Particularly noticeable with Note ON in paraphonic mode
  • Especially when the waveform is square wave, the noise of chorus delay component is noticeable at high frequency

Restricted Support for Arduino Nano

  • If you want to run this sketch in Arduino Nano (ATmega328), you must reduce the sketch size as follows (and sound quality in the high frequency range will be degraded):
    • Modify FOR_ARDUINO_NANO = false to FOR_ARDUINO_NANO = true in "generate-osc-table.rb", and execute this Ruby script
    • Alternatively, delete "osc-table.h", and rename "osc-table.h.FOR_ARDUINO_NANO.txt" to "osc-table.h"

VRA8-U CTRL

  • "vra8-u-ctrl.html": MIDI Controller (Editor) Application for VRA8-U, HTML App (Web App)
  • We recommend using Google Chrome, which implements Web MIDI API
  • On Windows, We recommend using loopMIDI (virtual loopback MIDI cable) to connect VRA8-U
    • On Mac, a virtual MIDI bus (port) can be created by using the IAC bus
  • Functions
    • VRA8-U CTRL converts Program Changes (#0-7 for PRESET, #8-15 for user programs) into Control Changes
    • When Program Change #127 is entered or Control Change #90 is changed from Off (63 or lower) to On (64 or higher), "Rand Ctrl" is processed
    • VRA8-U CTRL stores the current control values and the user programs (#8-15) in a Web browser (localStorage)
    • Current parameter values and user programs (#8-15) can be imported/exported from/to JSON files

Parameter Guide

MIDI Implementation Chart

Synthesizer Block Diagram

Monophonic/Legato Mode

graph LR
    O1[Osc 1]   --> M[Mixer] --> F[Filter] --> A[Amp] --> C[Chorus FX] --> AO[Audio Out]
    SO[Sub Osc] --> M
    O2[Osc 2]   --> M
    E[EG]      -.-> O1
    E          -.-> O2
    E          -.-> F
    L[LFO]     -.-> O1
    L          -.-> O2
    L          -.-> F
    AE[Amp EG] -.-> A
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Paraphonic Mode

graph LR
    V1O1[Voice 1<br/>Osc 1] --> V1G[Voice 1<br/>Gate] --> M[Mixer] --> F[Filter] --> A[Amp] --> C[Chorus FX] --> AO[Audio Out]
    V2O1[Voice 2<br/>Osc 1] --> V2G[Voice 2<br/>Gate] --> M
    V3O1[Voice 3<br/>Osc 1] --> V3G[Voice 3<br/>Gate] --> M
    V4O1[Voice 4<br/>Osc 1] --> V4G[Voice 4<br/>Gate] --> M
    E[EG]      -.-> V1O1
    E          -.-> V2O1
    E          -.-> V3O1
    E          -.-> V4O1
    E          -.-> F
    L[LFO]     -.-> V1O1
    L          -.-> V2O1
    L          -.-> V3O1
    L          -.-> V4O1
    L          -.-> F
    AE[Amp EG] -.-> A
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Recommended Circuit Diagram

Recommended Circuit Diagram

This image was created with Fritzing.

Actual Wiring Diagram

Actual Wiring Diagram

This image was created with Fritzing.

License

CC0

Digital Synth VRA8-U v2.2.8 by ISGK Instruments (Ryo Ishigaki)

To the extent possible under law, ISGK Instruments (Ryo Ishigaki) has waived all copyright and related or neighboring rights to Digital Synth VRA8-U v2.2.8.

You should have received a copy of the CC0 legalcode along with this work. If not, see http://creativecommons.org/publicdomain/zero/1.0/.