Android 6.0 (Marshmallow): How to play midi notes?

Question

I'm creating an app that generates live instrument sounds and I'm planning on using the new Midi API featured in Android Marshmallow (version 6.0). I've read the package overview document here http://developer.android.com/reference/android/media/midi/package-summary.html and I know how to generate Midi notes but i'm still unsure: how do I actually play these notes after I've generated their Midi data?

Do I need a synthesizer program to play Midi notes? If so, do I have to make my own or is one provided by Android or a 3rd party?

I am a novice with Midi so please be as descriptive as possible with your answer.

What i've tried so far: I've created a Midi manager object and opened an input port

MidiManager m = (MidiManager)context.getSystemService(Context.MIDI_SERVICE); 
MidiInputPort inputPort = device.openInputPort(index);

Then, i've sent a test noteOn midi message to the port

byte[] buffer = new byte[32];
int numBytes = 0;
int channel = 3; // MIDI channels 1-16 are encoded as 0-15.
buffer[numBytes++] = (byte)(0x90 + (channel - 1)); // note on
buffer[numBytes++] = (byte)60; // pitch is middle C
buffer[numBytes++] = (byte)127; // max velocity
int offset = 0;
// post is non-blocking
inputPort.send(buffer, offset, numBytes);

I've also set up a class to receive the midi note messages

class MyReceiver extends MidiReceiver {
    public void onSend(byte[] data, int offset,
            int count, long timestamp) throws IOException {
        // parse MIDI or whatever
    }
}
MidiOutputPort outputPort = device.openOutputPort(index);
outputPort.connect(new MyReceiver());

Now, here's where i'm most confused. The use case of my app is to be an all-in-one composition & playback tool for making music. In other words, my app needs to contain or use a virtual midi device (like an intent of another app's midi synthesizer). Unless someone already made such a synthesizer, I must create one myself within my app's lifecycle. How do I actually actually convert a received midi noteOn() into sound coming out of my speakers? I'm especially confused because there also has to be a way to programmatically decide what type of instrument the note sounds like it's coming from: is this also done in a synthesizer?

Midi support in Android Marshmallow is fairly new so I haven't been able to find any tutorials or sample synthesizer apps online. Any insight is appreciated.

Android 6.0 (Marshmallow): How to play midi notes?

3 Answers