Developing Android Applications with Adobe AIR

Raw Data and the Sound Spectrum

With the arrival of digital sound, a new art form quickly followed: the visualization of sound.

Note

A sound waveform is the shape of the graph representing the amplitude of a sound over time. The amplitude is the distance of a point on the waveform from the equilibrium line, also called the time-domain. The peak is the highest point in a waveform.

You can read a digital signal to represent sound in real time using amplitude values.

Note

Making Pictures of Music is a project run by mathematics and music academics that analyses and visualizes music pieces. It uses Unsquare Dance, a complex multi-instrumental piece created by Dave Brubeck. For more information, go to http://www.uwec.edu/walkerjs/PicturesOfMusic/MultiInstrumental%20Complex%20Rhythm.htm.

In AIR, you can draw a sound waveform using the computeSpectrum method of the SoundMixer class. This method takes a snapshot of the current sound wave and stores the data in a ByteArray:

SoundMixer.computeSpectrum(bytes, false, 0);

The method takes three parameters. The first is the container ByteArray. The second optional parameter is FFTMode (the fast Fourier transform); false, the default, returns a waveform, and true returns a frequency spectrum. The third optional parameter is the stretch factor; 0 is the default and represents 44.1 kHz. Resampling at a lower rate results in a smoother waveform and a less detailed frequency. Figure 11-1 shows the drawing generated from this data.

Figure 11-1. A waveform (top) ...