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mobileer-synth

General MIDI Synthesizer in portable C by Mobileer.

This synthesizer was licensed for use in the Palm Treo and other mobile devices for playing ringtones.

The library is given MIDI bytes as input and produces 16-bit PCM audio as output. It can be easily connected to any audio system. Optional output modules can be used to play in real-time using PortAudio or to output a WAV file.

The library has 3 levels:

  • ME1000 - is for low memory devices and uses a virtual analog synthesizer instead of wavetables
  • ME2000 - adds wavetables for piano, violin, drums and other instruments that are difficult to synthesize
  • ME3000 - adds support for DLS and Scalable Polyphonic MIDI ringtone standards

Documentation in docs folder

Dependencies and Requirements

The synthesizer uses 32-bit fixed-point arithmetic for its signal processing. It does not use floating point.

It has minimal software dependencies and can even run without a memory allocator on embedded devices with no operating system.

It does not require any file I/O. The wavetable instruments are loaded at compile time from a header produced by a custom editor.

The ME1000 requires:

  • Memory
    • Code 20-30 KB ROM
    • Instrument Library 14 KB ROM
    • Data 20-30 KB RAM
  • 32-bit integer arithmetic, eg ARM-7, Blackfin

The ME2000 adds more ROM for the wavetables, depending on quality. A 1 MB instrument set is included.

  • On an ARM946 generating audio at 44100 Hz
    • each wavetable voice requires 1.5 MIPS
    • each synthesized voice requires 2.4 MIPS

Building

The current build system requires CMake and a C compiler.

This will generate a library for the ME2000 and a few example programs.

cd spmidi
mkdir build
cd build
cmake ..
make

The libraries will be in the "spmidi/build/lib" folder and the executables will be in the "spmidi/build/bin" folder.

This will play a diatonic scale and output the results to a WAV file.

bin/play_scale

If you have ALSA installed then you can hear the output:

aplay spmidi_output.wav

You can convert any standard MIDI file to WAV using "play_midifile". We have included some ringtones that you can use for testing.

bin/play_midifile ../../data/ringtones/phil/songs/FurryLisa_rt.mid
aplay spmidi_output.wav
bin/play_midifile ../../data/ringtones/phil/songs/Bach_Sonata3EMajor.mid
aplay spmidi_output.wav

Contributors

  • Phil Burk - primary developer and sound designer
  • Robert Marsanyi - DLS and other contributions to the ME3000
  • Ryan Fransesconi - contributed to the instrument editor written in Java