Using the Media Classes - JavaFX 8: A Definitive Guide to Building Desktop, Mobile, and Embedded Java Clients - page 407

The createEQBands method begins by getting the list of EqualizerBand s from the AudioEqualizer associated
with the current MediaPlayer . The list is then cleared to make way for the bands that we want to create. The minimum
and maximum gains for an EqualizerBand on the current platform are accessible through the EqualizerBand.MIN_
GAIN and EqualizerBand.MAX_GAIN constants. These constants should always be used in calculations involving the
range of valid gain values. We use them to define the min, max, and mid (the midpoint of the gain range) variables. A
for loop then creates the number of EqualizerBand s defined by the BAND_COUNT constant, setting their gain values in
a nice cosine wave pattern. This pattern emphasizes the bass and high-range frequencies, which makes a nice set of
default values.
Afterward, a second for loop iterates through the list of EqualizerBand instances we just created and creates
a corresponding Slider control and frequency Label for each one. Each Slider is created by the createEQSlider
method. The new Slider 's value property is bidirectionally bound to the EqualizerBand 's gain property inside this
method. This is the crucial part that gives the user control of the band's gain. Note that each Slider is also given a
style class of eqSlider . We use this class later to add some nice styling to our equalizer display.
The final step in the createEQBands method is to set the alignment and grow constraints of the Slider and Label
and add them to the GridPane layout node. The Slider s are set to grow horizontally so that the GridPane will expand
to fill the width of the window. Of course, the same result could have been achieved by setting the Label s to grow, but
then we would also have had to reset the Label 's maximum size because all Label s, by default, have their maximum
size set equal to their preferred size. The Label s and Slider s populate rows one and two in the GridPane , leaving row
zero for the spectrum display.
MediaPlayer has four properties that deal with the frequency spectrum of the current audio track:
audioSpectrumListener , audioSpectrumInterval , audioSpectrumNumBands , and audioSpectrumThreshold . The
audioSpectrumListener property is an instance of the AudioSpectrumListener interface. You use MediaPlayer 's
setAudioSpectrumListener method to attach the listener, which then enables the computation of spectrum data and
sends periodic updates to the listener's spectrumDataUpdate method. Calling setAudioSpectrumListener again with
a null value turns off audio spectrum calculations and updates.
The audioSpectrumInterval property lets you control the interval at which updates are sent to the
AudioSpectrumListener . The value is specified in seconds, and its default value is 0.1 seconds, which means that
by default your listener will receive 10 spectrum updates per second. The number of spectrum bands that will be
reported to the listener is controlled by the audioSpectrumNumBands property. The audioSpectrumThreshold property
defines the minimum value that will be reported for a given spectral band. This value has a unit of decibels and must
be less than zero.
Listing 9-24 highlights the additions that need to be made to the createEQInterface method to create the
controls that display the audio frequency spectrum.
Listing 9-24. Creating the Frequency Spectrum Display
private void createEQInterface() {
final GridPane gp = (GridPane) getViewNode();
final MediaPlayer mp = songModel.getMediaPlayer();
createEQBands(gp, mp);
createSpectrumBars(gp, mp);
spectrumListener = new SpectrumListener(START_FREQ, mp, spectrumBars);
}
private void createSpectrumBars(GridPane gp, MediaPlayer mp) {
spectrumBars = new SpectrumBar[BAND_COUNT];
for (int i = 0; i < spectrumBars.length; i++) {
spectrumBars[i] = new SpectrumBar(100, 20);
spectrumBars[i].setMaxWidth(44);