Sequential Prophet Rev 2, User Manual

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24 25 Filter Sequential Prophet Rev2 User’s Guide Filter Envelope
The description of envelope behavior just given is true when the
amount
param-
eter is set to a positive value. But since this control is actually bipolar, it is possible to
set a negative amount of modulation. In this case, the envelopes are inverted and their
behavior changes. The best way to get a feel for the difference is to experiment with
both positive and negative settings of the
env amount
parameter.
The cutoff frequency setting may limit the effect of the envelope on the filter. For
example, in low-pass filter mode , if
cutoff
is at its highest setting, a positive envelope
amount will have no effect on the filter since the filter is already completely open.
Velocity: 0...127
—Allows key velocity to influence filter frequency. If
the
amount
is set to a positive value, the harder you play, the more the
filter will open and the brighter the sound will be. Conversely, if set to a
negative value, the harder you play, the more the filter will close and the
less bright the sound will be. This control makes for more touch-sensitive
sounds.
Key Amount: 0...127
—Sets the amount of modulation from the
keyboard to the filter’s cutoff frequency. Any setting above zero means
that the higher the note played on the keyboard, the more the filter opens.
This is useful for adding brightness to a sound as higher notes are played,
which is typically how acoustic instruments behave. When set to zero,
keyboard filter tracking is off, meaning that filter frequency is unaffected by
playing higher or lower notes on the keyboard. When set to 64, the filter
will track in half-step increments (which can be useful if you are using
the filter to generate a pitch through self-oscillation in 4-pole mode).
Audio Mod: 0...127
—Controls the amount of audio from Oscillator 1
used to modulate the filter cutoff frequency. It is useful for adding a bit
of harmonic movement and high end sizzle to many sounds, especially in
4-pole filter mode with some filter resonance.
To create bell-like FM sounds with
audio mod
, set the filter to 4-pole mode, set
audio mod
to 127, set
osc mix
to 127, set
osc
2
shape
to off, and set
osc
1
shape
to the
desired waveshape. Then turn
resonance
to 127 and experiment different
osc
1
freq
tunings, filter
cutoff
, and
key amount
settings. Adjust the filter and amplifier envelopes
as necessary.
Filter Envelope
The Prophet Rev2 filter has a dedicated, five-stage envelope generator
(DADSR). The Filter Envelope is used to shape the harmonic charac-
teristics of a synthesized sound by giving you filtering control over its
attack, decay, sustain, and release stages (plus a delay parameter to delay
the onset of the envelope).
This is one of the most important aspects of designing a sound. Without
an envelope, the filters would be completely static. They would stay
open or closed by a fixed amount that wouldn’t change over the duration
of a sound. That’s not very interesting to listen to and it’s not how instru-
ments behave in the real world.
In general, sounds produced by an instrument are brighter at their begin-
ning (the attack stage) and grow mellower as they die out (the decay
and release stages). In other words, their harmonic content changes over
time. This is exactly what the filter envelope is designed to emulate.
CUTOFF RESONANCE ENV AMOUNT VELOCITY KEY AMOUNT AUDIO MOD
4 POLE DELAY ATTACK DECAY SUSTAIN RELEASE
LOW-PASS FILTER
Filter Envelope
attack decay sustain release
amplitude
time
note off note on
delay
A typical 5-stage DADSR envelope