progressively increases as decay shortens, producing envelopes more typical of brass instruments.
The
MOD
knob controls how the brightness (filter cutoff frequency) is affected by the envelope. Starting
from the minimum setting, turning the knob clockwise will progressively increase the amount of envelope
modulation on the brightness - with the maximum amount reached when the knob is at noon. Then,
turning the knob will reduce the envelope amount, but will compensate by adding an offset. Thus, at 7
o’clock, there is no modulation and the filter is fully closed; and at 5 o’clock, there is no modulation and the
filter is fully opened.
Tip: adjust the VCA response curve, from exponential to linear, for more variations.
Tip: unplug the IN jack. This will patch a co3.3V source to the IN input, and the module will directly
output the internal envelope. Adjust the MOD knob for subtle variations in slew-rate; and of course the
exponential/linear control!
This mode emulates the mysterious response of a resistive opto-isolator (vactrol).
The
SHAPE
knob controls the slowness of the vactrol. Over the first half of the course of the knob, the
decay time of the vactrol increases, with a relatively small, proportional increase of the attack time. Over
the second half of the course of the knob, stranger contours are produced, in which the vactrol responds
“backwards”.
The
MOD
knob controls how much the brightness (filter cutoff frequency) follows the amplitude change to
further damp the sound. Starting from the minimum setting, turning the knob clockwise will progressively
increase the amount of filter damping - with the maximum amount reached when the knob is at noon.
Then, turning the knob will reduce the damping, but will compensate by adding an offset. Thus, at 7
o’clock, there is no modulation and the filter is fully closed; and at 5 o’clock, there is no modulation and the
filter is fully opened.
Tip: the model is correct when the VCA response curve is set to linear - but who cares about correctness?
Tip: unplug the IN jack. A “vactrolized” version of the signal on the
EXCITE
input will be produced on the
OUT
output.
In this mode, the signal on the
EXCITE
input is analyzed to extract two pieces of information: its amplitude
envelope, and its spectral centroid. The spectral centroid is a number indicating how “bright” a sound is.
With a bit of hand-waving, we could say that if the sound had been made with a low-pass filter, this would
be its cutoff frequency! The spectral centroid will be low for “dark” sounds, and high for “bright” sounds.
The two extracted parameters - envelope and centroid - are routed to the amplitude and frequency CV of
the VCFA. As a result, the signal routed to the IN input is modulated in amplitude and brightness to mimic
the signal on the EXCITE input. This gives a totally new dimension to the concept of an envelope follower!
The
SHAPE
knob controls the reaction time of the envelope follower. Over the first half of the course of
the knob, the detector goes from fast to muddy. Over the second half ot the course of the knob, the
detector goes from muddy to wobbly.
Mutable Instruments | Streams
4 of 8
