Communication/MIDI/render.cpp

Connecting MIDI devices to Bela!

Connect a USB MIDI device to Bela and try out our MIDI API. This example by default opens the MIDI port "hw:1,0,0", which normally corresponds to the first USB device that is plugged in. You can run amidi -l on the terminal to check which devices are available and edit this file accordingly. The device "hw:0,0,0" is (on Bela images v0.3 and above) a virtual MIDI device to the host computer over the USB port.

Every time a MIDI message comes in, the midiMessageCallback() function is called. In this example, we detect NoteOn messages and we use them to generate a sinewave with given frequency and amplitude. We can also write MIDI messages, by sending a sequence of bytes with writeOutput().

/*
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| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
#include <Bela.h>
#include <libraries/Midi/Midi.h>
#include <stdlib.h>
#include <cmath>

float gFreq;
float gPhaseIncrement = 0;
bool gIsNoteOn = 0;
int gVelocity = 0;
float gSamplingPeriod = 0;
int gSampleCount = 44100; // how often to send out a control change

/*
 * This callback is called every time a new input Midi message is available
 *
 * Note that this is called in a different thread than the audio processing one.
 *
 */
void midiMessageCallback(MidiChannelMessage message, void* arg){
        if(arg != NULL){
                rt_printf("Message from midi port %s ", (const char*) arg);
        }
        message.prettyPrint();
        if(message.getType() == kmmNoteOn){
                gFreq = powf(2, (message.getDataByte(0) - 69) / 12.f) * 440.f;
                gVelocity = message.getDataByte(1);
                gPhaseIncrement = 2.f * (float)M_PI * gFreq * gSamplingPeriod;
                gIsNoteOn = gVelocity > 0;
                rt_printf("v0:%f, ph: %6.5f, gVelocity: %d\n", gFreq, gPhaseIncrement, gVelocity);
        }
}

void sysexCallback(midi_byte_t byte, void* arg)
{
        printf("Sysex byte");
        if(arg != NULL){
                 printf(" from midi port %s", (const char*) arg);
        }
        printf(": %d\n", byte);
}

Midi midi;

const char* gMidiPort0 = "hw:1,0,0";

bool setup(BelaContext *context, void *userData)
{
        midi.readFrom(gMidiPort0);
        midi.writeTo(gMidiPort0);
        midi.enableParser(true);
        midi.getParser()->setCallback(midiMessageCallback, (void*) gMidiPort0);
        midi.getParser()->setSysexCallback(sysexCallback, (void*) gMidiPort0);
        gSamplingPeriod = 1 / context->audioSampleRate;
        return true;
}

enum {kVelocity, kNoteOn, kNoteNumber};
void render(BelaContext *context, void *userData)
{

// one way of getting the midi data is to parse them yourself
//      (you should set midi.enableParser(false) above):
/*
        static midi_byte_t noteOnStatus = 0x90; //on channel 1
        static int noteNumber = 0;
        static int waitingFor = kNoteOn;
        static int playingNote = -1;
        int message;
        while ((message = midi.getInput()) >= 0){
                rt_printf("%d\n", message);
                switch(waitingFor){
                case kNoteOn:
                        if(message == noteOnStatus){
                                waitingFor = kNoteNumber;
                        }
                        break;
                case kNoteNumber:
                        if((message & (1<<8)) == 0){
                                noteNumber = message;
                                waitingFor = kVelocity;
                        }
                        break;
                case kVelocity:
                        if((message & (1<<8)) == 0){
                                int _velocity = message;
                                waitingFor = kNoteOn;
                                // "monophonic" behaviour, with priority to the latest note on
                                // i.e.: a note off from a previous note does not stop the current note
                                // still you might end up having a key down and no note being played if you pressed and released another
                                // key in the meantime
                                if(_velocity == 0 && noteNumber == playingNote){
                                        noteOn = false;
                                        playingNote = -1;
                                        velocity = _velocity;
                                } else if (_velocity > 0) {
                                        noteOn = true;
                                        velocity = _velocity;
                                        playingNote = noteNumber;
                                        f0 = powf(2, (playingNote-69)/12.0f) * 440;
                                        phaseIncrement = 2 * M_PI * f0 / context->audioSampleRate;
                                }
                                rt_printf("NoteOn: %d, NoteNumber: %d, velocity: %d\n", noteOn, noteNumber, velocity);
                        }
                        break;
                }
        }
        */

        /*
         *
         * alternatively, you can use the built-in parser (only processes channel messages at the moment).
         *
        int num;
        while((num = midi.getParser()->numAvailableMessages()) > 0){
                static MidiChannelMessage message;
                message = midi.getParser()->getNextChannelMessage();
                message.prettyPrint();
                if(message.getType() == kmmNoteOn){
                        f0 = powf(2, (message.getDataByte(0)-69)/12.0f) * 440;
                        velocity = message.getDataByte(1);
                        phaseIncrement = 2 * M_PI * f0 / context->audioSampleRate;
                        noteOn = velocity > 0;
                        rt_printf("v0:%f, ph: %6.5f, velocity: %d\n", f0, phaseIncrement, gVelocity);
                }
        }
         */

        /*
         * A third alternative, the one currently active in this example, is to set a callback
         * which gets called every time a new input message is available.
         * See midiMessageCallback above.
        */

        // using MIDI control changes
        for(unsigned int n = 0; n < context->audioFrames; n++){
                float value;
                if(gIsNoteOn == 1){
                        static float phase = 0;
                        phase += gPhaseIncrement;
                        if(phase > M_PI)
                                phase -= 2.f * (float)M_PI;
                        value = sinf(phase) * gVelocity/128.0f;
                } else {
                        value = 0;
                }
                for(unsigned int ch = 0; ch < context->audioOutChannels; ++ch)
                        audioWrite(context, n, ch, value);
                // the following block sends a control change output every gSampleCount samples
                static int count = 0;
                if(count % gSampleCount == 0){
                        static bool state = 0;
                        state = !state;
                        midi_byte_t statusByte = 0xB0; // control change on channel 0
                        midi_byte_t controller = 30; // controller number 30
                        midi_byte_t value = state * 127; // value : 0 or 127
                        midi_byte_t bytes[3] = {statusByte, controller, value};
                        midi.writeOutput(bytes, 3); // send a control change message
                }
                ++count;
        }
}

void cleanup(BelaContext *context, void *userData)
{

}