Web Audio API

Chapter 6. Advanced Topics

This chapter covers topics that are very important, but slightly more complex than the rest of the book. We will dive into adding effects to sounds, generating synthetic sound effects without any audio buffers at all, simulating effects of different acoustic environments, and spatializing sound in 3D space.

theory: Biquad Filters

A filter can emphasize or de-emphasize certain parts of the frequency spectrum of a sound. Visually, it can be shown as a graph over the frequency domain called a frequency response graph (see Figure 6-1). For each frequency, the higher the value of the graph, the more emphasis is placed on that part of the frequency range. A graph sloping downward places more emphasis on low frequencies and less on high frequencies.

Web Audio filters can be configured with three parameters: gain, frequency, and a quality factor (also known as Q). These parameters all affect the frequency response graph differently.

There are many kinds of filters that can be used to achieve certain kinds of effects:

Low-pass filter

Makes sounds more muffled

High-pass filter

Makes sounds more tinny

Band-pass filter

Cuts off lows and highs (e.g., telephone filter)

Low-shelf filter

Affects the amount of bass in a sound (like the bass knob on a stereo)

High-shelf filter

Affects the amount of treble in a sound (like the treble knob on a stereo)

Peaking filter

Affects the amount of midrange in a sound (like the mid knob on a stereo)

Notch filter

Removes unwanted sounds in a narrow frequency ...