User Manual
18
Low-Pass Filter
Dave Smith Instruments
Low-Pass Filter
The Prophet 12 features one analog resonant low-pass lter per voice.
The lter is switchable between 2- and 4-pole modes and has a dedi-
cated ve-stage (delay/attack/decay/sustain/release) envelope generator,
capable of looping the delay, attack, and decay segments. There are also
controls for modulating the lter cutoff with the keyboard and envelope
amount with keyboard velocity.
4-Pole—Selects the lter conguration. When lighted, the lter is in
4-pole mode. A 4-pole, low-pass lter rolls off frequencies above the
cutoff frequency at a slope of 24dB per octave. When the button is off,
the lter is in 2-pole mode and has a slope of 12dB per octave and a
more gradual roll-off of the higher frequencies. Frequencies below the
cutoff pass through unaffected, hence the name “low-pass.”
Frequency: 0...164—Sets the low-pass lter’s cutoff frequency over
a range of more than 13 octaves, stepping in semitones. The cutoff
transistions smoothly across the values when the frequency is swept.
Resonance: 0...127—Emphasizes a narrow band of frequencies around
the cutoff frequency. In 4-pole mode, high levels of resonance can cause
the lter to self oscillate. In 2-pole mode, resonance is much more subtle
and self-oscillation does not occur.
Key Amount: 0...127—Sets the amount of modulation from the
keyboard to FreqUency (the lter’s cutoff frequency). A setting of 64 will
step the lter in semitone increments for each note, 32 would be quarter-
tones, and so on.
VelocityEnvelope Amount: 0...127—Enables keyboard velocity to
modulate the lter enveloPe amoUnt.
Envelope Amount: -127...127—Sets the amount of modulation from
the low-pass lter envelope to the low-pass lter frequency. The modula-
tion amount can be positive or negative, allowing for inverted envelope
control.
Note: The low-pass frequency setting may limit the effect of the
envelope on the lter. For example, if FreqUency is all the way up, a
positive envelope amount will have no effect on the lter.