Web Audio API

Chapter 4. Pitch and the Frequency Domain

So far we have learned about some basic properties of sound: timing and volume. To do more complex things, such as sound equalization (e.g., increasing the bass and decreasing the treble), we need more complex tools. This section explains some of the tools that allow you to do these more interesting transformations, which include the ability to simulate different sorts of environments and manipulate sounds directly with JavaScript.

theory: Basics of Musical Pitch

Music consists of many sounds played simultaneously. Sounds produced by musical instruments can be very complex, as the sound bounces through various parts of the instrument and is shaped in unique ways. However, these musical tones all have one thing in common: physically, they are periodic waveforms. This periodicity is perceived by our ears as pitch. The pitch of a note is measured in frequency, or the number of times the wave pattern repeats every second, specified in hertz. The frequency is the time (in seconds) between the crests of the wave. As illustrated in Figure 4-1, if we halve the wave in the time dimension, we end up with a correspondingly doubled frequency, which sounds to our ears like the same tone, one octave higher. Conversely, if we extend the wave’s frequency by two, this brings the tone an octave down. Thus, pitch (like volume) is perceived exponentially by our ears: at every octave, the frequency doubles.

Figure 4-1. Graph of perfect A4 and A5 tones side by side ...