Bela
Real-time, ultra-low-latency audio and sensor processing system for BeagleBone Black
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05-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().

/*
____ _____ _ _
| __ )| ____| | / \
| _ \| _| | | / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/ \_\
The platform for ultra-low latency audio and sensor processing
http://bela.io
A project of the Augmented Instruments Laboratory within the
Centre for Digital Music at Queen Mary University of London.
http://www.eecs.qmul.ac.uk/~andrewm
(c) 2016 Augmented Instruments Laboratory: Andrew McPherson,
Astrid Bin, Liam Donovan, Christian Heinrichs, Robert Jack,
Giulio Moro, Laurel Pardue, Victor Zappi. All rights reserved.
The Bela software is distributed under the GNU Lesser General Public License
(LGPL 3.0), available here: https://www.gnu.org/licenses/lgpl-3.0.txt
*/
#include <Bela.h>
#include <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);
}
}
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.setParserCallback(midiMessageCallback, (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)
{
}