Dark energy ii doepfer, Nuts and bolts of sound generation – Doepfer Dark Energy II User Manual

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Dark EnerGy II

DOEPFER

Nuts and Bolts of Sound Generation

The symmetrical

pulse wave (or “square wave”, pulsewidth =

50 %) contains odd harmonics only (see Fig.). An asymmetrical

pulsewave (often simply called “pulse wave”) contains all harmon-

ics with their amplitudes depending on the pulsewidth.

The more the pulsewidth deviates from the symmetrical 50 %,

the stronger the higher harmonics will influence the sound, i.e.

its timbre will become more “nasal”.

The

width of a pulse wave can be modulated by a low frequency

oscillator (LFO) or, less common, by an envelope generator. This

way the harmonic spectrum of the pulse wave does not remeain

static. The resulting sound is similar to the chorusing effect be-

tween two oscillators which are nearly perfectly in tune, i. e. uni-

son. The modulation frequency has to be very low (approx. 1 Hz

or lower) because otherwise the oscillator will sound out of tune.

The

triangular and sine waveforms have only a shallow harmonic

structure or, as in the case of the sine wave, no harmonics at all.

The triangular waveform contains only odd harmonics like the

sawtooth, but their amplitudes decrease by the factor two. With

the sawtooth wave, these overtones decrease in a linear fashion.

Modulation

The amount of harmonics of the crude timbral material is crucial for the possibilities in sound shaping with

the subsequent voltage-controlled filter (VCF). Subtractive sound synthesis using a VCF (see below) can

only attuenate or amplify harmonics that are already there. Therefore, the sine and triangular waves only

play a minor role here. When the VCF resonance is set to maximum , it can be used as a sine wave oscilla-

tor if one is required for a specific sound.

If a low frequency oscillator is available, it can be used for modulating

either the VCO pitch (frequency modulation = FM, also called “vibrato”)

or the pulse width (pulse width modulation = PWM). Simple LFOs deliver

frequencies in the range of 0.1 Hz to 10 Hz while more sophisticated ones

have a significantly wider range (0.01 Hz to 5 kHz) with switchable fre-

quency ranges for better adjustment.

Modulation frequencies within audio range should be dealt with in more

detail as they can produce very special results. If a VCO is modulated by

a frequency close to its own, a completely new sound will be created. In this case the VCO also produces

inharmonic overtones, i.e. tones whose frequencies are not proper multiples of the VCO frequency. This

acoustic phenomenon forms the basis of what is known as FM Synthesis which is used on several digital

synthesizers. If e.g. a VCO, oscillating at 1 kHz (1,000 Hz), is modulated by a frequency of 400 Hz, so-

called “side bands” around the the VCO frequency are created which are grouped symmetrically around the

VCO frequency as proper multiples of the modulation frequency.

For the example illustrated here, this would result in: 1,000 Hz – 1,400 Hz –11,800 Hz - 200 Hz, etc...

100%

Harmonics

100%

Harmonics