CLAVIA DMI AB CLAVIA NORD Rack 2X [77/114] Waveform

About Subtractive Synthesis Page 75

The length of the period determines the pitch (frequency) of the sound. The shorter the period, the high-

er the pitch. If you for example make the oscillator play at a frequency of 440Hz, there will be 440 periods

of identical Sawtooth waves generated per second.

Normally there are three ways to change the frequency of an oscillator:

▼ By making settings on the front panel.

On the Nord Lead for example, you have an “Oct Shift” setting for both oscillators and separate Semitone

and Fine Tune adjustments for Oscillator 2.

▼ By playing the keyboard.

The keyboard is if course connected to the oscillator so that pressing different key produces different

pitches. In some cases this connection can be turned off, so that the oscillator always plays the same

pitch, regardless of which key is pressed. In the Nord Lead, this can be done for Oscillator 2, by deacti-

vating “Kbd Track”.

▼ By Modulation

Modulation allows you to make the pitch vary “automatically”. The most common example is probably

to use an LFO to make pitch go up and down, to create a vibrato. But you can also put the pitch under

envelope control, or make the pitch vary with your striking force (velocity).

Waveform

The waveform of the oscillator affects its harmonic content and thereby its “sound quality” (timbre). The

three most common waveforms are sawtooth, pulse wave and triangle.

Looking at the shape of a waveform tells very little about how it sounds. Instead, there’s a better way to

draw it, called a spectrum. Let’s introduce some quick theory:

Mathematically, all waveforms can be considered as built from a number of harmonics, added together.

Each of the harmonics consists of a sine wave, the purest and simple waveform there is (a sine wave has

no harmonics at all). In other words, if you add a number of sine waves together, each one with its own

pitch (frequency) and volume (amplitude), then you can build any waveform you like.

The lowest harmonic is called the fundamental. The fundamental determines the basic pitch of the

sound. If the fundamental has a frequency of 440Hz, we will perceive the entire sound as having a pitch

of 440Hz.

Other harmonics are then added to the fundamental, called overtones. Normally the first overtone ap-

pears at a frequency twice the fundamental (in our example 880 Hz). The next harmonic appears at a

frequency three times the fundamental (in our example 1320Hz) and so on.

In a spectral display of a waveform you can see the frequency (pitch) of each harmonic and its amplitude

(level). This is done by drawing each harmonic as a line raising up from a horizontal scale.

Each line’s position on this scale indicates the harmonic’s frequency. The line furthest to the left is the

fundamental, the next is the first harmonic etc. To make life easier, one usually doesn’t label the horizon-

tal scale with frequency in Hz, but rather with the number of the harmonic.

One Period