Detect Note Changes in MIDI Sequencer

Question

Hi all,
I’m trying to detect when the MIDI Sequencer changes notes using some kind of a listener to detect when the note changes occur. My example program is able to detect the end of the sequence and I’d like to be able to detect note changes and print a message in a similar way. Here is my example code.
import javax.swing.*;
import javax.sound.midi.*;
public class SequencerTestApplet extends JApplet
    public void init()
        SequencerTest seqTest = new SequencerTest();
        seqTest.play();
        System.out.println("Print from init()");
class SequencerTest
    Sequencer sequencer=null;
    Sequence seq=null;
    Track track=null;
    public SequencerTest()
        try
        {   sequencer = MidiSystem.getSequencer();
            sequencer.open();
            // detect END OF SEQUENCE
            sequencer.addMetaEventListener(
                new MetaEventListener()
                {   public void meta(MetaMessage m)
                    {  if (m.getType() == 47) System.out.println("SEQUENCE FINISHED");
            sequencer.setTempoInBPM(40);
            seq = new Sequence(Sequence.PPQ, 16);
            track = seq.createTrack();
        catch (Exception e) { }
    public void play()
        try
        {    // NOTE 1
            ShortMessage noteOnMsg = new ShortMessage();
            noteOnMsg.setMessage(ShortMessage.NOTE_ON, 0, 60, 93);
            track.add(new MidiEvent(noteOnMsg, 0));
            ShortMessage noteOffMsg = new ShortMessage();
            noteOffMsg.setMessage(ShortMessage.NOTE_OFF, 0, 60, 93);
            track.add(new MidiEvent(noteOffMsg, 16));
            // NOTE 2
            ShortMessage noteOnMsg2 = new ShortMessage();
            noteOnMsg2.setMessage(ShortMessage.NOTE_ON, 0, 68, 93);
            track.add(new MidiEvent(noteOnMsg2, 16));
            ShortMessage noteOffMsg2 = new ShortMessage();
            noteOffMsg2.setMessage(ShortMessage.NOTE_OFF, 0, 68, 93);
            track.add(new MidiEvent(noteOffMsg2, 32));
            sequencer.setSequence(seq);
            sequencer.start();
        catch (Exception e) { }
}In this program the init() method starts the sequencer through the play() method and then continues on so that the “print from init()” statement is printed from the init() method while the sequencer is still playing. Then after the sequencer is finished, it uses the MetaEventListener to detect the end of the sequence and print the “sequence finished” message. I’d like to be able to make it also detect when the sequence changes notes in a similar way... Start the sequence and move on, but then be able to detect each time a note change occurs and print a message.
Since I am putting the notes at specific midi ticks (multiples of 16, or “quarter notes”) I could poll the Sequencer using getTickPosition() to see if the Sequencer’s tick position matches a particular multiple of 16. However, the problem with this is it would lock up the program since it would be constantly polling the sequencer and the program wouldn’t be able to do anything else while the Sequencer is playing (and I also have a loop option for the Sequencer so that would lock up the program indefinitely).
Here’s what I’ve found out and tried so far...
I read in this [this tutorial|http://java.sun.com/docs/books/tutorial/sound/MIDI-seq-adv.html] on the java sun site (under “Specifying Special Event Listeners”) that The Java Sound API specifies listener interfaces for control change events (for pitch-bend wheel, data slider, etc.) and meta events (for tempo change commands, end-of-track, etc.) but it says nothing about detecting note changes (note on/off). Also in the [EventListener API|http://java.sun.com/j2se/1.3/docs/api/java/util/class-use/EventListener.html] (under javax.sound.midi) it only lists the ControllerEventListener and the MetaEvenListener.
I also read here that MIDI event listeners listen for the end of the MIDI stream, so again no info about detecting note changes.
It seems like the sequencer should have some way of sending out messages (in some fashion) when these note changes happen, but I’m not sure how or even if it actually does. I’ve looked and looked and everything seems to be coming back to just these two types of listeners for MIDI so maybe it doesn’t.
To be sure the MetaEventListener doesn’t detect note changes I changed the MetaMessage from:
public void meta(MetaMessage m)
{    if (m.getType() == 47) System.out.println("SEQUENCER FINISHED");
}to:
public void meta(MetaMessage m)
{    System.out.println("" + m.getType());
}so that it would print out all of the MetaMessages it receives. The only message that printed was “47” which indicates the end of the sequence. So the MetaEventListener doesn’t appear to do what I need it to do.
I realize this is a rather odd problem and probably not many people have had the need to do something like this, but it never hurts to ask. If anyone has any suggestions on how to solve this problem it would be greatly appreciated.
Thanks,
-tkr

Answer 1

Tekker wrote:
As another idea, since I can't do it with a listener like I originally wanted to, would adding a separate thread to poll the sequencer and send an interrupt when it matches a particular midi tick be a good route to try? My thinking is this essentially act kind of like a listener by running in the background and reporting back when it changes notes.Yep, that worked! :)
import javax.swing.*;
import javax.sound.midi.*;
public class ThreadTestApplet extends JApplet
     public void init()
          ThreadTest threadTest = new ThreadTest();
          threadTest.play();
          MIDIThread thread = new MIDIThread(threadTest.sequencer);
          thread.start();
          System.out.println("  Print from init() 1");
          try { Thread.sleep(1000); } catch (InterruptedException ie) {}
          System.out.println("  Print from init() 2");
          try { Thread.sleep(1000); } catch (InterruptedException ie) {}
          System.out.println("  Print from init() 3");
          try { Thread.sleep(1000); } catch (InterruptedException ie) {}
          System.out.println("  Print from init() 4");
class ThreadTest
     Sequencer sequencer=null;
     Sequence seq=null;
     Track track=null;
     public ThreadTest()
          System.out.println("Sequencer Started");
          try
          {     sequencer = MidiSystem.getSequencer();
               sequencer.open();
               // detect END OF SEQUENCE
               sequencer.addMetaEventListener(
                    new MetaEventListener()
                    {  public void meta(MetaMessage m)
                         {     if (m.getType() == 47) System.out.println("SEQUENCER FINISHED");
               sequencer.setTempoInBPM(40);
               seq = new Sequence(Sequence.PPQ, 16);
               track = seq.createTrack();
          catch (Exception e) { }
     public void play()
          try
          {     // NOTE 1
               ShortMessage noteOnMsg = new ShortMessage();
               noteOnMsg.setMessage(ShortMessage.NOTE_ON, 0, 60, 93);
               track.add(new MidiEvent(noteOnMsg, 0));
               ShortMessage noteOffMsg = new ShortMessage();
               noteOffMsg.setMessage(ShortMessage.NOTE_OFF, 0, 60, 93);
               track.add(new MidiEvent(noteOffMsg, 16));
               // NOTE 2
               ShortMessage noteOnMsg2 = new ShortMessage();
               noteOnMsg2.setMessage(ShortMessage.NOTE_ON, 0, 68, 93);
               track.add(new MidiEvent(noteOnMsg2, 16));
               ShortMessage noteOffMsg2 = new ShortMessage();
               noteOffMsg2.setMessage(ShortMessage.NOTE_OFF, 0, 68, 93);
               track.add(new MidiEvent(noteOffMsg2, 32));
               sequencer.setSequence(seq);
               sequencer.start();
          catch (Exception e) { }
import javax.sound.midi.*;
public class MIDIThread extends Thread
     Sequencer sequencer=null;
     long midiTick=0;
     long midi_progressionLastChord=32;
     boolean print = true;
     public MIDIThread(Sequencer sequencer)
          this.sequencer = sequencer;
     public void run()
          System.out.println("Thread Started");
          while (midiTick<midi_progressionLastChord)
          {     midiTick = sequencer.getTickPosition();
               if (midiTick == 0 || midiTick == 16)
               {     if (print)
                    {     System.out.println("NOTE CHANGE");
                         print = false;
               else
                    print = true;
}I put in several print statements (with pauses in the init method) and the init print statements continue to be printed while the sequencer is playing, so it's not locking up the system and the "note change" statements happen when the sequencer changes notes. So this part is working perfectly! :)
Here's what I got for my output:
Sequencer Started
Print from init() 1
Thread Started
NOTE CHANGE
Print from init() 2
NOTE CHANGE
Print from init() 3
SEQUENCER FINISHED
Print from init() 4
The only problem I'm having is how to "throw" this action back up to the main init method and have it do the print statement instead of the thread class. Throwing an interrupt apparently won't work as you have to poll it to see if it has been interrupted (so it'd be no different than just polling the sequencer to see if it equals the specific midi tick). Maybe throw an ActionEvent? But how to attach it to my applet? Would I need to create an instance of my applet and then pass that into the thread class so it can catch the ActionEvent? And if I do that will it stop the thread or will it keep the thread running so can detect the other notes?... Or is there a better/simpler way to do this?
Thanks again,
-tkr