Moog Music MF-107 FreqBox User Manual

Page 12

VCO Waveforms

The timbre of the VCO is determined by its waveform. As defined

earlier, a waveform is related to the timbre, and the number of harmonics

in a sound. In many musical sounds, waveforms are really complex, and

change a lot over time, often both in frequency, timbre and amplitude.

This is not so with the raw signal of a VCO. Unlike most musical

instruments, a VCO is always vibrating. It will vibrate without changing

frequency, timbre, or amplitude with no change at its control input. A

VCO waveform can be represented with really simple graphs. There

are various types of waveforms, we will talk about the waveforms that

Figure 12: VCO Waveforms

are produced by the

FreqBox’s VCO and how

they sound.

One basic waveform

is the sawtooth

wave.(figure 12A). The

start of the waveform’s

cycle is a rapid jump

from low to high then the

waveform ramps down to

the bottom. A sawtooth wave contains all the harmonics of the harmonic

series, with the amplitude of each harmonic decreasing by the same ratio

it increases, i.e. the 2

harmonic is 2X the frequency of the fundamental,

but 1⁄2 the amplitude of the fundamental. The rest of the harmonics

continue in this manner. Because of all these harmonics, the sawtooth

wave can be described as very bright and buzzy.

Another waveform is the square wave (figure 12B). A cycle of a

square wave has two equally timed portions (the high and low), making

it a symmetrical waveform. It has only odd harmonics (3X, 5X, 7X, etc),

with each harmonic following the same basic amplitude relationship as

the sawtooth wave (The 3

harmonic is 3X the fundamental frequency

and 1/3 the fundamental amplitude). The square wave sounds bright but

also a little hollow (somewhat like a clarinet).

A square wave is a type of rectangular wave (figure 12C), it happens

to be symmetrical. The width of the high portion of a rectangular wave

is known as the pulse width, and can be expressed as a percentage. For

instance, a square wave has a pulse width of 50%. When a rectangular

wave is assymetrical, it is called a pulse wave. As the pulse width gets

much smaller or larger than 50% the sound becomes thin and reedy,