Media

see also : Robovox

User Manual

Version 1.4

The Kraftor Robovox MIDI is a MIDI-controlled interface for the Votrax SC-02 speech synthesizer chip. It allows you to trigger phonemes and control various speech parameters via MIDI.

Version History

• v1.4 (2026-04-02) : fixed a pitch issue
• v1.3 (2026-01-27): Added Channel 2 pitch control for singing mode, improved SC-02 initialization
  for external inflection mode
• v1.2 (2026-01-27): Added Serial MIDI support (USB + DIN MIDI simultaneously)
• v1.1 (2025-07-20): Initial release

MIDI Channel Configuration

The base MIDI channel is set via the 4 DIP switches on the hardware. The channel is read as a binary
number (0-15).

DIP Switch Settings

The rightmost switch (DIP4) is the least significant bit (value 1). Switches are ON when in the DOWN position.

Two-Channel Operation

The device uses two consecutive channels:

For example, if DIP switches are set to channel 1 (only DIP4 ON):

• Channel 1 = Phonemes
• Channel 2 = Pitch

MIDI Messages

Note On/Off (Channel N) – Phoneme Control

MIDI notes trigger the SC-02’s phonemes. The mapping covers notes 36 to 103 (C2 to G7).

• Note On: Triggers the phoneme with the specified velocity
• Note Off: Triggers PA0 (silence/pause) phoneme

Note On (Channel N+1) – Pitch Control (NEW in v1.3)

Send MIDI notes on the second channel to control the pitch of the voice for “singing” mode.

• Range: MIDI notes 36-120 (C2 to C9)
• Uses a pre-calculated pitch lookup table for accurate musical notes
• Send pitch notes before or during phoneme playback to set the singing pitch

Usage Example:

1. Send Note 60 (C4) on Channel 2 → Sets pitch to middle C
2. Send Note 46 (A) on Channel 1 → Voice sings “A” phoneme at C4 pitch

Note: Pitch control only works with the internal carrier. When using an external carrier (CC64 >
63), the pitch comes from the external audio source.

Velocity (7-bit value)

The velocity of Note On messages controls the amplitude/volume of the phoneme.

Pitch Bend – Coarse Pitch Control (14-bit value)

The pitch bend wheel provides coarse pitch control by adjusting the LTC6903 master clock frequency.

This affects the overall clock rate of the SC-02, providing a wide pitch range.

CC2 – Fine Pitch / Inflection (7-bit value)

Control Change 2 (Breath Controller) provides fine pitch control by directly
writing to the SC-02’s inflection register.

Use this for subtle pitch variations, vibrato, or pitch modulation effects.

CC1 – Mod Wheel / Filter (7-bit value)

Control Change 1 (Modulation Wheel) controls the SC-02’s vocal tract filter
frequency.

This changes the “timbre” or formant characteristics of the voice.

CC3 – Speech Rate (7-bit value)

Control Change 3 controls the speech rate (speed of phoneme articulation).

CC64 – Sustain / Carrier Select (7-bit value)

Control Change 64 (Sustain Pedal) switches between internal and external carrier.

When using an external carrier, you can feed audio into the SC-02 for vocoder-like effects.

Quick Reference Table

Connections

The Robovox MIDI accepts MIDI via:

• USB MIDI (primary)
• Serial MIDI on Serial MIDI TRS type B

Both inputs are active simultaneously and are handled by the same handlers.

Tools

Robovox Translator

This tool helps sequence text into phonemes, while also allowing duration and pitch adjustment. Test the sequence by connecting the page to Robovox. It also allows you to save the sequence as a MIDI clip.

Robovox translator

Github code

You can also run it directly from this url : https://deladriere.github.io/Robovox_translator/

Firmware

Do not use this firmware for Emy or Emy Terminal.

How to install the firmware on Kraftor

Robovox MIDI for Kraftor

1 file(s) 121.50 KB

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