Sound Synthesis - Phase distortion

Phase distortion as a means of synthesizing sounds is the last type in our discussion of how synthesizers produce different kinds of sounds. It has some similarities to Frequency Modulation synthesis in as much as they both are built on phase modulation. Before we can discuss it however, we have to define what phase modulation is.

Without getting into trigonometry and calculus, the best way to describe phase modulation is that it consists of two signals, a carrier signal and a modulating signal. The carrier signal is usually a sine wave, which most people will recognize as the smooth curve pictured below.

The modulating signal is pictured below (in red) superimposed upon a short wave length (in green) sine wave, along with the resulting phase modulated wave (in blue) below it

As you can see, the wavelength and shape of carrier sine wave has been changed in several places as a result of the combination.

Phase distortion uses this concept to change sine waves to sawtooth waves by distorting phase angle of the wave so that the left side of the sine wave is more vertical as pictured below.

The resulting wave is not exactly a sawtooth because it has a smooth curve instead of a straight line on the right side of the curve. In the same sense a square wave can be produced by increasing the amplitude of the wave and cutting of the top of the wave.(see below) It’s a little more complicated than that but that’s what the end result is.

Page 2—What does it sound like?