Making Waves with Java—An Adventure in Midi
My wife and I use one of those sound-generator boxes when we go to sleep at night to drown out any surrounding noise. Recently, we were visiting my mom and discovered that we should have packed the sound generator in our suitcase. It seems that her next-door neighbor has a very annoying dog named Henry who barks at us all night. You'd think he had discovered a stadium full of mailmen! I decided to see if I could use Java to make my own sound generator.
My first thought was that I could create an audio file containing white noise. After looking over the new javax.sound.sampled package in JDK 1.3, however, I decided that unless I could figure out the format for one of the supported audio files, I was out of luck. I happened to remember, though, that my Midi synthesizer has a wave sound—maybe I had it on Windows, too (most sound drivers for Windows include a Midi synthesizer that plays sounds on your speaker just like they were WAV files). I decided to explore the javax.sound.midi API, also new to JDK 1.3.
I am by no means a Midi expert. I have a synthesizer, and I have used Midi programs in the past, so I am at least a little familiar with Midi. Basically, Midi is a protocol for musical instruments. You can chain multiple Midi devices together, and each device has its own specific ID. Some devices only play music; others only generate notes. Some devices, like my synthesizer, generate notes and also play them. Each device has a number of channels (usually 16), which function a little like sessions. The idea is that you can make each channel function as a different instrument and play different notes.
A Midi patch describes an instrument. It contains a sound bank number (a synthesizer typically has a number of different sound banks containing many instruments) and a program number, which is the index number of the instrument in the particular sound bank. To change the instrument on a channel, you issue a program change request, supplying a new patch (instrument).
To play musical notes, you simply send the channel a "note on" request, giving the pitch value (a number between 0 and 127, where 64 is middle C) and the velocity, which indicates how hard you want the note struck. For example, on a piano, when you hit a key harder, the sound is louder. Midi supports the same concept, and some synthesizers even have velocity-sensitive keys. When you want the note to stop, you send a "note off" request. Midi has other interesting requests, such as "pitch bend," which enables you to change the pitch of the note on the fly. On a synthesizer, you often see a pitch-bend wheel off to the left that can raise or lower the pitch. It's basically the same effect that you get on a guitar when you push the string out of position. A single channel can typically support a number of simultaneous notes. To play a chord, you don't need to use separate channels; just send three "note on" requests.
One of the interesting aspects of the synthesizer is that a drum kit is a single instrument. For instance, you may have an instrument called Jazz Drums in which each different note is a different drum. A single note might represent cymbals, a high hat, or even a whistle. You might need to play around with the synthesizer a bit to figure them out.
In starting my sound-generator project, I had never used the Java Midi API, so I had to take a few guesses about where to start. From my limited knowledge of Midi, I knew that my initial goal was just to be able to send a note on a channel and hear it played.
Looking at the API, the MidiSystem class sure looks like the main entry point into the system—and, sure enough, it has a method to return the default synthesizer. That certainly looks like a good place to start. You simply call getSynthesizer like this:
Synthesizer synth = MidiSystem.getSynthesizer();
Looking at the Synthesizer class, you can see that it has a getChannels method, so that looks like the best way to get a channel. It also has open and close methods (inherited from the MidiDevice parent class), so obviously you need to open the synthesizer device before you can use it. You simply call the open method like this:
synth.open();
Looking at the MidiChannel interface, you can see that it has noteOn and noteOff methods, so it's a pretty good guess that you can use these to play notes. You just call getChannels on the Synthesizer class to get the available channels, and then you play a note on one of the channels:
MidiChannel[] channels = synth.getChannels(); channels[1].noteOn(64, 127);
You want to give the note some time to play before you shut it off. I tried doing a Thread.sleep before shutting it off:
Thread.sleep(2000); channels[1].noteOff(64);
Finally, when you're done with the synthesizer, you should close it:
synth.close();
When I ran my first test program, I noticed that it never terminated even after I closed the synthesizer. Obviously the Midi library was doing something in the background that prevented the program from terminating. I threw in a call to System.exit to get it to quit properly.
At this point, I had a program that could play a C note on what sounded like a piano. Here is the complete program:
import javax.sound.midi.*;
public class Note
{
public static void main(String[] args)
{
try
{
// Locate the default synthesizer
Synthesizer synth = MidiSystem.getSynthesizer();
// Open the synthesizer
synth.open();
// Get the available Midi channels - there are usually 16
MidiChannel channels[] = synth.getChannels();
// Play a note on channel 1
channels[1].noteOn(64, 127);
// Give the note some time to play
Thread.sleep(2000);
// Turn the note off
channels[1].noteOff(64);
// Close the synthesizer device
synth.close();
// Terminate the program
System.exit(0);
}
catch (Exception exc)
{
exc.printStackTrace();
}
}
}
Okay, I knew that I could play a note. The next task was to play a note that sounded like the ocean. I didn't know the bank number or the patch number for the ocean sound—and, for that matter, I didn't know the name of the instrument. The Synthesizer class contains a getLoadedInstruments method that returns a list of all the instruments loaded into the sound bank. I tried calling it and I got a zero-length array—there were no instruments loaded.
The Synthesizer class also contains a loadAllInstruments method, so I had a way to load instruments—but loadAllInstruments takes a Soundbank object as a parameter. Seeing that the Synthesizer class had a getDefaultSoundbank method, I tried the following code:
Soundbank bank = synth.getDefaultSoundbank(); synth.loadAllInstruments(bank);
Sure enough, when I called getLoadedInstruments, I got a bunch. I listed them out using the following code:
Instrument instrs[] = synth.getLoadedInstruments();
for (int i=0; i < instrs.length; i++)
{
System.out.println(instrs[i].getName());
}
Somewhere in that huge list of names, I saw Seashore, so I changed the loop to look for an instrument named Seashore. Now that I had the instrument, I needed to figure out how to change the channel to use the instrument. I knew that I needed to issue a program change on the channel, and the programChange method takes a program number (really an instrument number) and an optional sound bank. The Instrument class doesn't have a program number or a sound bank number, but it does have a getPatch method that returns a Patch object that does contain a program number and a sound bank.
I called programChange on the channel like this:
Patch seashorePatch = seashore.getPatch();
channels[1].programChange(seashorePatch.getBank(),
seashorePatch.getProgram());
Sure enough, when I played the C note, I heard an ocean sound. The only problem left was that the ocean sound was a little too regular for me. I didn't think I could go to sleep with such a simple sound repetition. I decided to start five different ocean sounds with slightly different pitches and at staggered intervals so that the sounds should run together. I ended up with the following program, which, I am happy to say, drowned out Henry's annoying bark.
import javax.sound.midi.*;
public class Waves
{
public static void main(String[] args)
{
try
{
// Locate the default synthesizer
Synthesizer synth = MidiSystem.getSynthesizer();
// Open the synthesizer
synth.open();
// Get the available Midi channels - there are usually 16
MidiChannel channels[] = synth.getChannels();
// Get the synth's soundbank where all the sounds are stored
Soundbank bank = synth.getDefaultSoundbank();
// Load all the available instruments
synth.loadAllInstruments(bank);
// Get a list of the available instruments
Instrument instrs[] = synth.getLoadedInstruments();
Instrument seashore = null;
// Loop through the instruments
for (int i=0; i < instrs.length; i++)
{
// Stop when you find the seashore
if (instrs[i].getName().equals("Seashore"))
{
seashore = instrs[i];
break;
}
}
if (seashore == null)
{
System.out.println("Can't find the beach");
System.exit(0);
}
// Get the information describing the Seashore instrument - the
// patch contains the soundbank and program number
Patch seashorePatch = seashore.getPatch();
// Set 5 channels to use the Seashore instrument
channels[1].programChange(seashorePatch.getBank(),
seashorePatch.getProgram());
channels[2].programChange(seashorePatch.getBank(),
seashorePatch.getProgram());
channels[3].programChange(seashorePatch.getBank(),
seashorePatch.getProgram());
// Start the Seashore note on 3 different channels. By waiting a short
// time before starting the next note, you get a much more continuous sound
channels[1].noteOn(32, 127);
Thread.sleep(3500);
channels[2].noteOn(32, 127);
Thread.sleep(1500);
channels[3].noteOn(32, 127);
// Wait forever
for (;;)
{
try { Thread.sleep(999999999); } catch (Exception ignore) {}
}
}
catch (Exception exc)
{
exc.printStackTrace();
}
}
}
The entire development process for this little project took no more than 30 minutes. If you have at least a small idea how Midi works, the Midi API is very intuitive. Bravo, Javasoft!
About the Author
Mark Wutka is the president of Wutka Consulting and specializes in helping companies get the most out of Java. He has built numerous Java, JSP, and servlet applications, including several online ordering applications. In a past life, he was the chief architect on a large, object-oriented distributed system providing automation for the flight operations division of a major airline; for nine years he designed and implemented numerous systems in Java, C, C++, and Smalltalk for that same airline. Mark previously contributed chapters to Special Edition Using Java 2 Platform and is the author of Special Edition Using Java Server Pages and Servlets and Hacking Java. His next book, Special Edition Using Java 2 Enterprise Edition, will be available in April.