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Basics of Soundgeneration
Dark EnerGy
DOEPFER
There are several ways to
control the filter’s cutoff frequency
. First, it can be adjusted manually with the
Freq. knob. Furthermore the ADSR as well as LFO 2 can influence the cutoff frequency with any intensity.
The intensity is set by the XM knob. Additionally, the filter is controllable via MIDI, i.e. its cutoff frequency
can be controlled by any MIDI controller and / or by the velocity data of the incoming MIDI notes. Finally,
using a switch, you can determine whether the VCF cutoff frequency tracks the VCO frequency fully, half
or not at all (keyboard tracking, keyboard follow). Filter resonance can be adjusted until self oscillation of
the filter occurs. Similar applies to the VCO-LFO (LFO 1) with regard to the LFO for the filter (LFO 2). LFO
2 can also produce frequencies up to the audio range. The tonal results of VCF frequency modulation with
audio frequencies are similar to those of the VCO. You can create typical FM metallic sounds especially
with high frequencies whether you use tonal base material (VCO / external audio signal) or not. You can
even create voice-similar sounds when setting the VCF to the appropriate setting and using slowly pro
-
gressing ADSR envelopes. The sound will become realy extreme, if you use frequency modulation with au
-
dio frequencies for both VCF and VCO. The tonal results are nearly unpredictable. There is only one way:
try it out; very often the results are totally surprising.
Very unusual in analogue synthesizers but musically useful is the linear frequency modulation, featured by
Dark Energy. Here the VCFs cutoff frequency is modulated in a linear matter by the triangle wave of the
VCO. Intensity is set by the LM knob. This feature is very useful for FM sounds with the filter working as
a sinewave oscillator (self oscillating) that keep their harmonic content while the sound is e.g. played by a
sequencer, keyboard or USB/MIDI interface.
Amplifiers
The voltage controplled amplifier (VCA) emphases the sound between the factor 0 and 1, depending on a
control voltage, usually provided by the envelope generator and/or the LFO. The VCA controls the loudness
contour of the sound, resp. their articulation, to use a musical term.
The above described components VCO, VCF and VCA generate resp. process the audiosignal itself. Next
to this, we already mentioned components that do not generate any audible signals, but provide control
voltages to modulate the parameters of the soundprocessing modules. These are the envelope generator
(or ADSR) and the Low Frequency Generator (LFO).
Envelope Generators
Envelope generators, typically of the ADSR type (attack - decay -
sustain - release), produce a sequence of four voltages which can
be used for controlling the VCO pitch, VCF cutoff frequency and
the VCA amplification. The ADSR produces a “one shot” contour
in opposite to an LFO, which generates a frequent modulation.
The envelope consists of 4 parameters: attack time, decay time,
sustain level and release time. When pressing a key on a key-
board (note-on command / gate = on), the envelope rises within
a period of time which can be set by the attack control. After
reaching its maximum the envelope decays down to the sustain
level within a period of time adjustable by the decay control. The
envelope stays on this level until the key is released (note-off
command / gate = off). Then it decreases to zero within a period
of time adjustable with the release control.
: ADSR-Hüllkurve und ihre Parameter
Sustain
Level
Attack
Time
Decay
Time
Release
Time
+3 ... +12 V
0 V
On
Off
Zeit
ca. +8 V
