Midiverb/Midiverb II emulator

January 16, 2026 · View on GitHub

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There's a VST3 plugin now. Also a WEB DEMO!

What is this

This is an emulator for the original Midiverb, Midifex and Midiverb II effect units made by Alesis.

The core is DASP-family DSP processor µ-code emulator.

There's a decompiler that outputs C code which makes it possible to run at full-speed which is exactly what is done for the VST-3 plugin.

Contents of the repository

command-line emulator
disassembler/decompiler of DSP µ-code
VST3 plugin which is available for download in releases
web demo which is live here

Support

All of Midiverb, Midifex and Midiverb II are fully supported with these exceptions:

Triggers for flanger are not implemented
Pre-emphasis/antialiasing filter modelling, output filter modelling

`midiverb` CLI tool

This is a simple command-line tool for adding effects to wav files.

It supports two modes:

emulation, which requires original ROMs to run (midiverb.rom, midifex.rom or midiverb2.rom)
using internal decompiled Midiverb effects - that doesn't require the ROMs but not all features are supported

How to build it:

requires libsndfile to build: apt-get install libsndfile-dev
then just make

Example usage

Inputs and outputs are stereo WAV files, 23.4 KHz, 16-bit, signed integer. The effect doesn't resample the input so if you run wavs at 48 KHz you will run the effect twice as fast.

$ sox i_feel_so_liberated.wav -t wav -e signed-integer -b 16 -r 23400 input.wav

By default internal implementation of effects from Midiverb II is used. The effect programs are numbered the same way as on the original unit. The following example runs 100% wet effect no. 15 from Midiverb II.

$ ./midiverb 15 input.wav output.wav
using internal decompiled effects for MidiVerb 2
effect name: Medium Bright 1.1 Sec
channels=2, sample_rate=23400, num=93600

midiverb supports wet/dry mixing and feedback. This runs 40% wet effect no 15 from midiverb with 50% feedback.

$ ./midiverb -m midifex 15 -d 0.4 -f 0.5 input.wav output.wav
using internal decompiled effects for MidiFex
effect name: ECHO SHORT LPF AMBI
channels=2, sample_rate=23400, num=93600

You can also run the original roms. This runs flanger:

$ ./midiverb -r roms/midiverb2.rom -d 0.5 52 input.wav output.wav
detected ROM: MidiVerb 2
effect name: Flange Pan 2
this effect has LFO
channels=2, sample_rate=23400, num=93600

Midiverb decompiler

A decompiler from Midiverb instruction set to C. It will also disassemble the ROMs.

It does some optimizations:

delay-line identification
dead code elimination
constant folding
calculating partial results in floating-point (that's by default, but integer calculation can be set by an option)

The decompiler doesn't yet support LFO, because the LFOs rely in dynamically modifying the effect code and patching different offset and constants. This will be supported in the future.

The output of the decompiler looks something like this (full output here):

void effect_22(int16_t input, int16_t *out_left, int16_t *out_right, int16_t DRAM[0x4000], int ptr) {
  int16_t Acc, tmp1, tmp2, tmp3, tmp5;
  WRITE_LINE(0, 0) = input;
  Acc = -LINE(8, 14810, 11) / 4 + -LINE(6, 13099, 796) / 4 + -LINE(4, 10902, 1001) / 4;
  tmp3 = -Acc;
  Acc = -LINE(8, 14810, 11) / 4 + -LINE(6, 13099, 445) / 4 + -LINE(4, 10902, 336) / 4;
  tmp5 = -Acc;
  Acc = LINE(0, 0, 1) / 2 + LINE(2, 8564, 1) / 2;
  WRITE_LINE(2, 8564) = Acc;
  Acc = LINE(2, 8564, 1) * 81 / 32 + LINE(14, 16381, 160) / 2;
  WRITE_LINE(14, 16381) = -Acc;
  Acc = -Acc / 2 + LINE(14, 16381, 160) + LINE(13, 16219, 215) / 2;
  WRITE_LINE(13, 16219) = -Acc;
  Acc = -Acc / 2 + LINE(13, 16219, 215) + LINE(12, 16002, 434) / 2;
  WRITE_LINE(12, 16002) = -Acc;
  Acc = -Acc / 2 + LINE(12, 16002, 434) + LINE(11, 15566, 557) / 2;
  WRITE_LINE(11, 15566) = -Acc;
  Acc = -Acc / 2 + LINE(11, 15566, 557) + LINE(10, 15007, 117) / 2;
  WRITE_LINE(10, 15007) = -Acc;
  Acc = -Acc / 2 + LINE(10, 15007, 117) + LINE(9, 14888, 76) / 2;
  WRITE_LINE(9, 14888) = -Acc;
  Acc = -Acc / 2 + LINE(9, 14888, 76);
  tmp2 = Acc;
  Acc = LINE(8, 14810, 712) * 5 / 8 + LINE(7, 14096, 995) / 2;
  WRITE_LINE(7, 14096) = -Acc;
  Acc = -Acc / 2 + LINE(7, 14096, 995);
  WRITE_LINE(6, 13099) = Acc;
  Acc = LINE(6, 13099, 1005) * 3 / 4 + LINE(5, 12092, 1188) / 2;
  WRITE_LINE(5, 12092) = -Acc;
  Acc = -Acc / 2 + LINE(5, 12092, 1188);
  WRITE_LINE(4, 10902) = Acc;
  Acc = LINE(4, 10902, 1028) * 3 / 4 + LINE(3, 9872, 1306) / 2;
  WRITE_LINE(3, 9872) = -Acc;
  Acc = -Acc / 2 + LINE(3, 9872, 1306);
  tmp1 = Acc;
  Acc = LINE(1, 8561, 1) / 2 + tmp1 / 2;
  WRITE_LINE(1, 8561) = Acc;
  Acc = WRITE_LINE(1, 8561) + tmp2;
  WRITE_LINE(8, 14810) = Acc;
  *out_left = tmp5;
  *out_right = tmp3;
}

Usage

The decompiled-midiver.h file was generated with

python3 disasm.py -d decompiled-midiverb.h -i midiverb.rom --prefix midiverb_

Midiverb VST3 plugin

There is a plugin using the JUCE library that works very much like the "internal" effects in midiverb tool but can be run as a VST3 plugin with realtime parameters. This plugin was generated using Claude Code.

There are precompiled binaries in releases.

Building on Windows

Get MSVC from https://visualstudio.microsoft.com/downloads/ - you need "Desktop development with C++"
Open "Developer Command Prompt for VS ..."
Clone the plugin: git clone https://github.com/thement/midiverb_emulator
In the terminal:

cd path\to\MidiverbPlugin
mkdir build
cd build
cmake ..
cmake --build . --config Release

After that in one of the build subdirectories there should be a MidiverbPlugin.vst3 plugin ready.

Supported ROMs

The effect ROM is not distributed with this program and you have to obtain it yourself. If you own a MIDIVERB/MIDIFEX unit and don't want to dump the EEPROM yourself, you might look for a synthesizer rom archive.

This program was tested with the following roms:

MD5SUM	ROM name
11a460c8e64d3325411bba0c11a2ae49	midiverb.rom
f06003307a93ec09c637146ecaa17948	midifex.rom
d503f74c239917b9888f247f979509ec	midiverb2.rom

Authors

The Midiverb I emulator is based on reverse engineering work done by Eric Brombaugh and there's a series of videos presenting this work by Paul Schreiber. If you are into synthesizers and electronics, it's a must watch!

The Midiverb II was reverse-engineered by myself (thement).