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

Strictly speaking this only applies to pure sine wave frequency modulation, i.e. if both, VCO and LFO,

are sine wave oscillators. With other waveforms further (in)harmonic overtones will be added. Inhar-

monic sounds, similar to frequency modulation, are also produced by pulsewidth modulation at high

frequencies. In practice, this principle is used for creating extremely inharmonic sounds. The degree

of being inharmonic depends on the strength (amplitude) of LFO modulation as well as on the fre-

quency ratio between VCO and LFO. “Experimentation is better than theory” applies here. You should

try various settings for LFO frequency and LFO amplitude. Most probably the resulting waveforms are

not ideal for sweet, “beautiful” timbres but can be used for more extreme, “vicious” sounds instead.

Your neighbors will love you!

Filters

With subtractive sound synthesis, the further processing of the tonal “crude material” (VCO signal)

will be done by a voltage-controlled filter (VCF) first which is usually followed by a voltage-controlled

amplifier (VCA).

There are different

types or characteristics of filters. The

basic types are low pass, band pass, and high pass while

the types notch and allpass are less common. The filter

types differ in how they pass the frequency resp. which fre-

quency ranges are rejected. A low pass passes all frequen-

cies below the cutoff frequency and cuts off all frequencies

above. The high pass works just the other way round since

it lets all frequencies that are above the cutoff frequency

pass and cuts off all frequencies below. A band pass lets all

frequencies within a certain range (band) pass and rejects

all frequencies outside this range. A notch cuts out a cer-

tain frequency range (inverse function of the bandpass). An

allpass lets all frequencies pass but it performs a phase-shift

depending on the frequency. All these filter types have a dif-

ferent and musically interesting effect on the treated sound.

Dark Energy II uses a multimode filter that can continously

crossfade between lowpass, notch, highpass and bandpass.

Apart from the type of VCF, another important parameter

of a filter is its

slope which is measured in dB/octave. It

describes how steep the transition from passing to rejec-

tion is. The “ideal” filter would have an infinite slope, i.e.

the transition occurs immediately (e.g. 999 Hz would pass

totally while 1,000 Hz would be suppressed completely). In

reality, this transition is not aprupt but continuous, depend-

ing on the filter’s slope. For musical purposes, a high-quality

filter would have a slope of 24 dB/octave or 12 dB/octave.

The latter are very useful for special applications (usually for

high pass, band pass, and notch). Dark Energy II uses a

12 dB/octave multimode filter which offers lot’s of sonic

capabilities.

A further filter parameter is

resonance (or emphasis). If the filter has an adjustable resonance, fre-

quencies around the cutoff point can be emphasized. The filter will become more of a band pass with

an underlying low pass. For musical applications it is very important that the filter resonance is adjust-

able. VCFs without adjustable resonance are rarely used. Overtones around the cutoff point are em-

phasized the higher the resonance value is. This yields the resonating and “twittering” sounds typical

of an analog filter. On many filters the resonance can be set to such a high level that self-oscillation

of the filter occurs (even without any input). This allows you to use the filter as a sine wave oscillator

Charakteristics of a lowpass filter

Lowpass, highpass, bandpass and notch

Out

Freq.

Out

Freq.

Low Pass

High Pass

Out