This library replicates the functionality of an old school Yamaha synthesizer, i'm not aiming to perfection, or creating an emulator, i just want to create something that sounds good enough.
It uses FM synthesis (don't tell anyone, but it actually is PM) to simulate various instruments, 80's style.
Checkout an interface demonstrating what can be done with it, called WMO Operator.

• Up to 132 keys (on any desired frequency)
• Up to 6 oscillators per key (can play as many keys as your CPU can handle)
• Breakpoint / Level Scaling / Keyboard Tracking / Keyboard Following
• Use one of the classic 4 and 6 operator algorithms
• Load voices from SYSEX files (some settings can produce A LOT of noise or sound very different...)
• Filters (high pass, low pass, band pass, distortion, etc...)

WIP!

The idea is that you instantiate an Instrument, pass a Preset, and finally, press and release a key. Midi support is being worked on.
Presets can be obtained from DX7 sysex files using the Dx7Sysex utilitarian class, which reads bulk exported voices and returns a list of presets, one for each voice.
Audio is obtained via 16bit PCM samples, created by calling the one of the "getFrame" method variants (getByteFrame, getShortFrame, or getFloatFrame).

This example utilizes Java AudioSystem to play the samples, it is a very basic use case.
See WMO Operator for another example, it uses LibGdx key press and release events to trigger the Instrument.

final List<InstrumentPreset> presetsList = Dx7Sysex.extractInstruments(new File("rom1a.syx"));
final Instrument instrument = new Instrument(44100);
instrument.setPreset(presetsList.get(20)); // preset 20 should be VIBES 1 on the cartridge dump used

/*
    we are creating a child thread because writing to the audio output is a blocking operation
    so we want this part to work without being bothered
*/
final Thread thread = new Thread(() -> {
    final AudioFormat audioFormat = new AudioFormat(44100, 16, 2, true, true);

    try (final SourceDataLine dataLine = AudioSystem.getSourceDataLine(audioFormat)) {
    
        // initializes the audio output
        dataLine.open(audioFormat);
        dataLine.start();
    
        // this blocks the thread, and have to be called as long as we want to play
        while (true) {
            // an audio frame have 4 bytes, 2 for each 16bit channel ([8bit L][8bit L]-[8bit R][8bit R])
            dataLine.write(instrument.getByteFrame(true), 0, 4);
        }
    } catch (LineUnavailableException e) {
        e.printStackTrace();
    }
});
thread.start();

// wait just a little for the audio initialization
Thread.sleep(500);

// this is from Stairway to Heaven intro
final KeyboardNote[] notes = new KeyboardNote[]{KeyboardNote.A_4, KeyboardNote.C_5, KeyboardNote.E_5, KeyboardNote.A_5, KeyboardNote.B_5};

// now we play then with 0.4s of duration, and 0.2s spacing
for(KeyboardNote note : notes){
    instrument.pressKey(note);
    Thread.sleep(400);
    instrument.releaseKey(note);
    Thread.sleep(200);
}

• Proper README/documentation
• A demo interface
• Pitch envelope
• Break points
• Envelope rate/speed scaling
• Transpose
• Improve feedback
• LFO
• Filters running in parallel (aggregate the results of various filters, instead of just applying one filter after another)
• Filter serialization
• More filters
• Channel separation/manipulation
• Instrument presets
• API fine tuning
• Parameters fine tuning
• MIDI support