Doepfer Dark Energy II - Manual (Page 14)

14
Dark EnerGy II DOEPFER Functions
3.2.2. VCF
Filters are a very important tool on every analog synthesizer. Filters modify sounds by rejecting some
frequencies while allowing others to pass in order to tweak the harmonic spectrum of a sound. There are
different types of filters. Each one rejects different frequency ranges and therefor has a different effect on
the treated sound. Most common and musically most useful filter types are:
• Lowpass: rejects high frequencies and passes low ones.
• Highpass: rejects low frequencies and passes high ones.
• Bandpass: rejects both high and low frequencies and passes a certain frequency band.
• Notch: rejects a frequency band and generates a ”notch”.
Dark Energy II uses a multimode filter that is capable of generating all four types of filter characteristics.
Continous crossfading between the types is possible.
The frequency rejection of all filter types has a certain strenght (”quality”). The frequency where the re-
jection starts is called ”cutoff frequency” (for high- and lowpass) or ”center frequency” (for bandpass and
notch). This point can be controlled by a pot or modulated by a control voltage in order to achieve dynamic
timbral shifts.
Another important filter term is „resonance“. Filter resonance emphasizes the harmonics around the cutoff
/ center frequency point. The sound will become increasingly „sharper“ and „edgier“. At a certain level, the
filter will start to self-oscillate and generate a waveform close to a sinewave. Dark Energy II‘s VCF can
also be driven into self-oscillation in order to use it as an additional signal source for certain popular sound
effects which are immediately recognizable as „typically synthesizer“.
The VCF gives you the following controls:
• Manual frequency control (Freq.)
This pot allows you to control the cutoff / center frequency of the VCF manually. In
other words, it is up to you to „open“ and „shut“ the „window“ of the filter (low- and
highpass) or „shift” it up and down the frequency range (notch and bandpass). Turned
fully clockwise, the filter will be opened completely and the entire frequency range
of the incoming signal can pass. Depending on the filter mode (see below) the Freq-
knob acts differently: Turned fully counter-clockwise, the lowpass filter will be closed
to an extent that all audible frequencies will be rejected and no output signal will be
audible. The highpass works vice versa. The further this knob is turned clockwise, the
lesser the effect of the envelope (ADSR) on the sound will be Bandpass and notch will
not be opened or closed but will pass different frequency ranges. The entire frequency
range of Dark Energy II‘s filter covers approx. 12 octaves.
• XFM control
In order to achieve dynamic and periodic changes of timbre, the cutoff frequency
can be modulated by control voltages. The XFM knob determines the modulation
depth. Set to center position, no modulation will appear, while turned fully clockwise
/ counter clockwise means maximum positive resp. negative modulation depth. The
modulation depth will be added to the setting of the manual frequency knob. Since
the sum of both cannot exceed the maximum value of the cutoff parameter range, the
Resonance changes the filter characteristics
fc
Resonance
Frequency
0 db
Attenuation
The resonance characteristics of a
lowpass filter
fc
Out
Freq.
Out
Freq.
Low Pass High Pass
fc fc . q e r F . q e r F
Out Out
fc
h c t o N s s a P d n a B