Digital Synth VRA8-N v2.5.1

• 2021-06-05 ISGK Instruments
• https://github.com/risgk/digital-synth-vra8-n

Concept

• Monophonic Synthesizer (MIDI Sound Module) for Arduino Uno

Caution about Arduino: Sorry for Mac users

• We strongly recommend Arduino IDE 1.8.5 (more precisely Arduino AVR Boards core 1.6.20)
  • If you use other than AVR Boards core 1.6.20 (or modified this sketch), the sketch may not work well
    • CPU Busy LED (LED L) may almost always lit, rather than flashing occasionally
• However, with macOS Catalina 10.15, only IDE 1.8.10 (AVR Boards core 1.8.1) or later can be used!
• If you have to use Arduino AVR Boards core 1.8.1, it is recommended to reduce the program size. Please do the following:
  • Change REDUCE_OSC_TABLE_SIZE_1 = false to REDUCE_OSC_TABLE_SIZE_1 = true in "generate-osc-table.rb", and execute this
    • Requiring a Ruby execution environment
  • Or delete "osc-table.h", and rename "osc-table.h.REDUCE_OSC_TABLE_SIZE_1.txt" to "osc-table.h"

Change History

• v2.5.1
  • Fix wave tables (Reduce noise)
• v2.5.0
  • Fix downward portamentos
  • Add generate-osc-table for Digital Synth VRA8-N pSAW-16
    • Digital Synth VRA8-N pSAW-16: VRA8-N Special Edition with 16-step Pseudo-SAW Wave
• v2.4.4
  • Prevent increase of CPU load in AVR Boards core 1.8.1
    • Change comments for macOS Catalina 10.15 and Arduino IDE 1.8.10 (AVR Boards core 1.8.1)
  • Improve portability of "make-sample-wav-file.cc"
  • Add "osc-table.h.REDUCE_OSC_TABLE_SIZE_1.txt"
• v2.4.3
  • Fix "make-sample-wav-file.cc" (for Debugging on PC): Add #define ENABLE_OSC_2
• v2.4.2 (Major Changes)
  • Improve ENABLE_SPECIAL_PROGRAM_CHANGE option: Works when the CC value changes from <= 63 to >= 64
• v2.4.1 (Major Changes)
  • Fix explanation about Arduino AVR Boards (Core)
    • "There is no restriction on a version of Arduino AVR Core" was a mistake!
  • Add comments for macOS Catalina 10.15 and Arduino IDE 1.8.10 (AVR Boards 1.8.1)
  • Change "LEGATO" of "PRESET #4 PAN FLUTE" from ON to OFF
  • Reset "EXPRESSION" when "EXP BY VEL" turns OFF
  • Add ENABLE_SPECIAL_PROGRAM_CHANGE option: Program Change by Control Change #112-119, and #90
• v2.4.0 (Major Changes)
  • Add the JSON file IMPORT/EXPORT function to VRA8-N CTRL
  • Rename the constants for CCs
  • Introduce NewEnvGen (Level changes are smoother than the original EnvGen)
  • Improve the ANALOG_INPUT_REVERSED option of mode-VC
• v2.3.0 (Major Changes)
  • Do not support Arduino Nano 3.x (because the sketch uses more than 30720 bytes of program storage space)
  • Rename VRA8-N mini to VRA8-N mode-VC
  • Improve VRA8-N mode-VC: Add the SCALE MODE "C Major" and the GATE Signal support
  • Halve the send level of LFO > CUTOFF for smoothness
  • Change the change range of CUTOFF frequency from 28-124 to 16-112 (64: the center)
  • Change the Q of RESONANCE 64 from 2.8 to 2.0 (No change in the range of Q from 0.7 to 8.0)
  • Add "PITCH > CUTOFF", "OSC LEVEL", "RESONANCE LIMIT", "AMP LEVEL", and "DAMP AND ATTACK" controls
  • Reset EXPRESSION at Random Control
• v2.2.1
  • Fix the issue that RANDOM of LFO and the fluctuation of OSCs do not work
• v2.2.0 (Major Changes)
  • Enable Sub Oscillator in VRA8-N mini mode
  • Slow down the change speed of OSC MIX and SUB LEVEL
  • Improve stability: Reduce distortion of audio output when processing MIDI data
• v2.1.2
  • Add USE_PITCH_CV_IN option for VRA8-N mini (Undef it, if you use a MIDI keyboard)
• v2.1.1
  • Change the assignment of the potentiometers for VRA8-N mini
• v2.1.0 (Major Changes)
  • Narrow the CUTOFF frequency range from 5 oct (G4-G9) to 4 oct (G5-G9) for sound quality
  • Add OSC2 NOISE; Change "OSC1/2 (SAW/SQ)" to "OSC1/2 (SAW/N/SQ)"
  • Add "LFO FADE TIME" control
  • Add LFO LED Out option (Enabled by default, Pin D5)
  • Add Pin D5 Audio Out option for MIDI Shield (Disabled by default)
  • Add the operation mode VRA8-N mini option (Voltage controlled, Sub Oscillator disabled)
  • Improve stability
• v2.0.1
  • Fix sound quality degradation in v2.0.0
  • Revert "SUSTAIN (OFF/ON)" to "SUSTAIN"
• v2.0.0 (Major Changes)
  • Change "OSC (SAW/SQ)" to "OSC1/2 (SAW/SQ)"
  • Add "EXPRESSION", "EXP > CUTOFF", "EXP > AMP LEVEL", and "EXP BY VEL (OFF/ON)"
• v1.2.1
  • Improve sound quality
  • Improve VRA8-N CTRL compatibility between versions
• v1.2.0 (Major Changes)
  • Add "EG > PITCH(-/+)", "EG > P. TGT (1&2/2)", "RELEASE (OFF/ON)", and "EG > LFO RATE (-/+)"
  • Change "OSC2 MIX" (OSC2 Max 50%) to "OSC MIX (1/2)" (OSC2 Max 100%)
  • Change "SUB WAVE (SIN/SQ)" to "SUB (SIN/NOISE/SQ)"
  • Change "AMP (GATE+RLS/EG)" to "AMP EG (OFF/ON)" (No Release)
  • Change "SUSTAIN" to "SUSTAIN (OFF/ON)"
  • Change "LFO WAVE (TRI/SQ)" to "LFO (T/2/SA/RND/SQ)"
  • Change "LFO > PITCH (2/1+2)" to "LFO > PITCH (-/+)" and "LFO > P. TGT (1&2/2)"
  • Change "KEY ASGN (LO/LAST)" to "K. ASN (L/L/P/H/LST)"
  • Change the variation range of "CUTOFF" 7-127 to 4-124
  • Change the names of controllers
  • Change the layout and the display of VRA8-N CTRL
  • Change PRESETs
• v1.1.0 (Major Changes)
  • Add "SUB WAVE (SIN/SQ)" and "LFO WAVE (TRI/SQ)"

Features

• Sampling Rate: 31.25 kHz, Bit Depth: 8 bit, LPF Attenuation Slope: -12 dB/oct
• Serial MIDI In (38.4 kbps), PWM Audio Out (Pin D6), Optional PWM LFO LED Out (Pin D5), PWM Rate: 62.5 kHz
  • We recommend adding a RC filter circuit to reduce PWM ripples
    • A cutoff frequency 15.9 kHz (R: 100 ohm, C: 100 nF) works well
  • CAUTION: The Arduino PWM audio output is a unipolar Line Out
    • Please connect the output to a active speaker/a power amp/a headphone amp
    • Do not connect the output to a passive speaker/a headphone directly
  • CAUTION: Click sounds may occur when you connect the audio out to an amp or reset the board
• We recommend Hairless MIDI<->Serial Bridge to connect PC
  • NOTE: A combination of a MIDI Shield (MIDI Breakout) and a power supply adapter is recommended to avoiding USB noise
    • To use MIDI Shield, edit SERIAL_SPEED, LFO_LED_OUT_ACTIVE, and SUBSTITUTE_PIN_D5_FOR_D6_AS_AUDIO_OUT in "DigitalSynthVRA8N.ino"
    • Even using only the power supply adapter significantly reduces USB noise
• Files
  • "DigitalSynthVRA8N.ino" is a sketch for Arduino/Genuino Uno Rev3 (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-N CTRL

• MIDI Controller (Editor) for VRA8-N, HTML5 App (Web App)
• VRA8-N CTRL converts Program Changes (#0-7 for PRESET) into Control Changes
• VRA8-N CTRL stores the current control values and the user programs (#8-15) in a Web browser (localStorage)
• We recommend Google Chrome, which implements Web MIDI API
• We recommend loopMIDI (virtual loopback MIDI cable) to connect VRA8-N
• CAUTION: Low CUTOFF with high RESONANCE can damage the speakers
• CAUTION: Click sounds may occur when you change the control values

Details of Controllers

• "OSC1/2 (SAW/N/SQ)": OSC1 Wave / OSC2 Wave
  • Values 0-15: OSC1 SAW / OSC2 SAW
  • Values 16-63: OSC1 SAW / OSC2 SQUARE
  • Values 40-63: OSC1 SAW / OSC2 NOISE
  • Values 64-87: OSC1 SQUARE / OSC2 NOISE
  • Values 88-111: OSC1 SQUARE / OSC2 SAW
  • Values 112-127: OSC1 SQUARE / OSC2 SQUARE
• "SUB (SIN/NOISE/SQ)": SUB Osc Wave
  • Values 0-31: SIN
  • Values 32-95: NOISE
  • Values 96-127: SQUARE
• "LFO (T/2/SA/S&H/SQ)": LFO Wave
  • Values 0-15: Triangle (Key Trigger: Off)
  • Values 16-47: Triangle 2 (Key Trigger: On)
  • Values 48-79: SAW Down (Key Trigger: On)
  • Values 80-111: RANDOM (Key Trigger: On)
  • Values 112-127: SQUARE Up (Key Trigger: On)
• "LFO FADE TIME": This affects "LFO DEPTH" but not "MODULATION DEPTH"
• "PITCH > CUTOFF": In other words, Filter CUTOFF Keyboard Tracking (Off/Half/Full)
• "LEGATO (OFF/ON)": LEGATO Portamento
  • When LEGATO Portamento is ON, Single Trigger is forced
• "K. ASN (L/L/P/H/LST)": Key ASSIGN / Trigger Mode
  • Values 0-47: Lowest Note / Single Trigger
  • Values 48-79: Paraphonic (Lowest and Highest Notes, Duophonic) / Single Trigger
  • Values 80-111: Highest Note / Single Trigger
  • Values 112-127: LAST One Note / Multi Trigger
• "EXP BY VEL (OFF/ON)": EXPRESSION Control By (Note ON) VELOCITY
• "DAMP AND ATTACK": DAMP the EG level to zero before ATTACK (0-63: Off, 64: Slowest, 127: Fastest)

A Sample Setting of a 4-Knob Physical Controller

+---------------+---------------+---------------+---------------+
| CC #16        | CC #17        | CC #23        | CC #19        |
| CUTOFF        | RESONANCE     | ATTACK        | DECAY         |
+---------------+---------------+---------------+---------------+

VRA8-N mode-VC (Alternative Operation Mode)

• VRA8-N is Voltage Controlled by 0-5V signals
• By default, you need 4 potentiometers and 2 buttons
  • A0: CUTOFF
  • A1: RESONANCE
  • A2: OSC MIX
  • A3: Pitch CV In (0V: Note OFF)
  • D2: Change the PROGRAM (#0, ..., #7, Random Control)
  • D4: Change the SCALE MODE
    • SCALE MODE 0: "C Major" (2Oct / 5V)
    • SCALE MODE 1: "Chromatic" (2Oct / 5V)
    • SCALE MODE 2: "Linear" (5Oct / 5V)
• To make the sketch operate as VRA8-N mode-VC, edit ENABLE_VOLTAGE_CONTROL in "DigitalSynthVRA8N.ino"
  • If you use a MIDI keyboard, comment out the line #define USE_PITCH_CV_IN
• See "cv-in.h"
  • If you use a GATE Signal (A5), cancel comment out of the line //#define USE_GATE_IN
• NOTE: A power supply adapter is strongly recommended to avoiding the swings of voltage values

MIDI Implementation Chart

  [Monophonic Synthesizer]                                        Date: 2021-06-05       
  Model: Digital Synth VRA8-N     MIDI Implementation Chart       Version: 2.5.1         
+-------------------------------+---------------+---------------+-----------------------+
| Function...                   | Transmitted   | Recognized    | Remarks               |
+-------------------------------+---------------+---------------+-----------------------+
| Basic        Default          | x             | 1             |                       |
| Channel      Changed          | x             | x             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| Mode         Default          | x             | 3             |                       |
|              Messages         | x             | x             |                       |
|              Altered          | ************* |               |                       |
+-------------------------------+---------------+---------------+-----------------------+
| Note                          | x             | 0-127         |                       |
| Number       : True Voice     | ************* | 0-120         |                       |
+-------------------------------+---------------+---------------+-----------------------+
| Velocity     Note ON          | x             | o (V=1-127)   | When EXP BY VEL is ON |
|              Note OFF         | x             | x             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| After        Key's            | x             | x             |                       |
| Touch        Ch's             | x             | x             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| Pitch Bend                    | x             | o             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| Control                     1 | x             | o             | MODULATION DEPTH      |
| Change                     11 | x             | o             | EXPRESSION            |
|                               |               |               |                       |
|                            24 | x             | o             | OSC1/2 (SAW/SQ)       |
|                            25 | x             | o             | OSC MIX (1/2)         |
|                            20 | x             | o             | OSC2 COARSE (-/+)     |
|                            21 | x             | o             | OSC2 FINE (-/+)       |
|                               |               |               |                       |
|                            29 | x             | o             | SUB (SIN/NOISE/SQ)    |
|                            26 | x             | o             | SUB LEVEL             |
|                           104 | x             | o             | EG > PITCH (-/+)      |
|                           105 | x             | o             | EG > P. TGT (1&2/2)   |
|                               |               |               |                       |
|                            16 | x             | o             | CUTOFF                |
|                            17 | x             | o             | RESONANCE             |
|                            18 | x             | o             | EG > CUTOFF (-/+)     |
|                            31 | x             | o             | AMP EG (OFF/ON)       |
|                               |               |               |                       |
|                            23 | x             | o             | ATTACK                |
|                            19 | x             | o             | DECAY                 |
|                            27 | x             | o             | SUSTAIN               |
|                            28 | x             | o             | RELEASE (OFF/ON)      |
|                               |               |               |                       |
|                            14 | x             | o             | LFO (T/2/SA/RND/SQ)   |
|                            80 | x             | o             | LFO RATE              |
|                            82 | x             | o             | LFO > PITCH (-/+)     |
|                            83 | x             | o             | LFO > CUTOFF (-/+)    |
|                               |               |               |                       |
|                            81 | x             | o             | LFO DEPTH             |
|                             3 | x             | o             | EG > LFO RATE (-/+)   |
|                             9 | x             | o             | LFO > P. TGT (1&2/2)  |
|                            15 | x             | o             | LFO FADE TIME         |
|                               |               |               |                       |
|                            85 | x             | o             | P. BEND RANGE         |
|                            86 | x             | o             | PITCH > CUTOFF        |
|                           106 | x             | o             | EXP > CUTOFF (-/+)    |
|                           107 | x             | o             | EXP > AMP LEVEL       |
|                               |               |               |                       |
|                            22 | x             | o             | PORTAMENTO            |
|                            30 | x             | o             | LEGATO (OFF/ON)       |
|                            87 | x             | o             | K. ASN (L/L/P/H/LST)  |
|                            89 | x             | o             | EXP BY VEL (OFF/ON)   |
|                               |               |               |                       |
|                           108 | x             | o             | OSC LEVEL             |
|                           109 | x             | o             | RESONANCE LIMIT       |
|                           110 | x             | o             | AMP LEVEL             |
|                           111 | x             | o             | DAMP AND ATTACK       |
|                               |               |               |                       |
|                   90, 112-119 | x             | x             | (RESERVED)            |
+-------------------------------+---------------+---------------+-----------------------+
| Program                       | x             | o             |                       |
| Change       : True #         | ************* | 0-7, 127      | 127: Random Control   |
+-------------------------------+---------------+---------------+-----------------------+
| System Exclusive              | x             | x             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| System       : Song Pos       | x             | x             |                       |
| Common       : Song Sel       | x             | x             |                       |
|              : Tune           | x             | x             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| System       : Clock          | x             | x             |                       |
| Real Time    : Commands       | x             | x             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| Aux          : Local ON/OFF   | x             | x             |                       |
| Messages     : All Notes OFF  | x             | o 123-127     |                       |
|              : Active Sense   | x             | x             |                       |
|              : Reset          | x             | x             |                       |
+-------------------------------+---------------+---------------+-----------------------+
| Notes                         |                                                       |
|                               |                                                       |
+-------------------------------+-------------------------------------------------------+
  Mode 1: Omni On,  Poly          Mode 2: Omni On,  Mono          o: Yes                 
  Mode 3: Omni Off, Poly          Mode 4: Omni Off, Mono          x: No