GarageBand-like waveform motion in Swing

Question

I have written a custom JPanel that paints an audio waveform to itself after converting the audio file to a double[] representation and bandpass filtering. Needless to say, that takes a while to do, about half a second on my computer.
Now I would like the the waveform to move smoothly across the screen so that the current audio position stays in the middle of the visible portion of the JPanel. (This is what Apple's GarageBand does when audio is being played back). I need this motion to occur without the waveform panel itself recomputing the waveform drawing every time the visible portion of the wave is shifted.
What is the best way to achieve this effect? So far I have considered:
1) Overriding the waveform JPanel's paintComponent() method so it returns an off-screen buffer any time the waveform itself has not changed. At that point I could just stick the JPanel in a JScrollPane and programmatically scroll it.
2) Programmatically scroll a JScrollPane containing my wave JPanel as described in (1), but find some way to override the "new" scrolling algorithm (described in the API) which repaints the underlying component on every move. This way I would not need to maintain an offscreen buffer for the waveform JPanel.
Maybe there is some better way? How do people generally scroll JComponents that are very expensive to repaint()?
I would appreciate advice on this one, perhaps with a link to an example! Thanks in advance.

Answer 1

FYI, your applet and program do not launch on my computer.
App error:
JNLPException[category: Launch File Error : Exception: null : LaunchDesc:
<jnlp spec="1.0" codebase="http://www.pscode.org/sound/" href="http://www.pscode.org/sound/audiotrace.jnlp">
  <information>
    <title>Audio Trace 1.0</title>
    <vendor>Andrew Thompson</vendor>
    <homepage href="http://www.pscode.org/sound//<p>
Audio Trace shows an oscilloscope or lissajous style trace of the
sounds currently playing through your computer. 
</p>
<p>
A variety
of scroll, zoom and fade effects can be applied to the trace
for visual interest.
</p>"/>
    <description kind="one-line">Audio Trace - oscilloscope style sound trace application.</description>
    <description kind="tooltip">Audio Trace</description>
    <icon href="http://www.pscode.org/sound/audiotrace-64x64.gif" height="64" width="64" kind="default"/>
    <icon href="http://www.pscode.org/sound/audiotrace-32x32.gif" height="32" width="32" kind="default"/>
    <shortcut online="false">
      <desktop/>
      <menu submenu="PSCode"/>
    </shortcut>
    <offline-allowed/>
  </information>
  <security>
    <all-permissions/>
  </security>
  <update check="timeout" policy="always"/>
  <resources>
    <java href="http://java.sun.com/products/autodl/j2se" version="1.3+"/>
    <jar href="http://www.pscode.org/sound/audiotrace.jar" download="eager" main="true"/>
  </resources>
  <application-desc main-class="org.pscode.sound.AudioTrace"/>
</jnlp> ]
     at com.sun.javaws.LaunchDownload.getMainClassName(LaunchDownload.java:1037)
     at com.sun.javaws.Launcher.doLaunchApp(Launcher.java:1075)
     at com.sun.javaws.Launcher.run(Launcher.java:105)
     at java.lang.Thread.run(Thread.java:613)
Applet error:
NoClassDef for MultipleGradientPaint