Warp 1.5: Sound
Let me quickly introduce you to a convenient tool for generating
sound output from a Java applet. The
class is part of the non-standard (and rather
sparsely documented) sun.audio package. Basically, an AudioDataStream
object works the same way as an InputStream (and is in fact a subclass
of it), except that it can be fed into the
object (also part of sun.audio) and be heard as sound.
When used correctly, AudioDataStreams perform the same way as the more
and take up as much memory. The difference is that
you can't manipulate or create AudioClips inside a Java applet. They have
to be created in advance and imported. But an AudioDataStream is just
like any InputStream object. You can let an applet build one from scratch
and fill it with whatever you like. That's what I did in this game.
The way sound data has to be coded in order to come out of the speakers
as something recognizable is far from trivial, however. There is a rough
conversion table listed on my Rainbow Notes melody
editor documentation pages and you can check the source code of that applet
to see how I compute it. A more time-consuming but easier way is to
use, for example, Billy Donahue's (firstname.lastname@example.org)
Now for something about the basic structure of my sound effects...
The sound of the spaceship firing is a square waveform with an exponentially
decaying amplitude and a frequency dropping from very high to low, sort
of like in this graph:
The crash & explosion sounds also have exponential decays, but their
waveforms are (almost) random. That's usually referred to as noise.
What you hear as a "plink" when a bullet hits an indestructible object is
a slightly perturbed square waveform, with a faster decay.
The sound of an enemy bullet being fired is related to the spaceship firing
sound, but starts out at a lower frequency and drops faster. Finally, the
weird bonus sound has a frequency that quickly and repeatedly
goes from low to high.
What is the advantage of using AudioDataStreams instead of AudioClips, since
I could obviously have recorded or generated all of these sounds in advance?
Well, for one thing you don't have to waste time downloading them over
a slow Internet connection. Even on a relatively sluggish machine, the 44
kilobytes of sound data used in this game get computed in less than a
second. Faster than a modem any day.