4ms EnvVCA Посібник користувача - Сторінка 9
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Fundamentals of the Follow Jack
The Follow jack causes the envelope to rise or fall in order to "follow" the signal on the jack. There are
two basic rules that govern this behavior:
Rule 1: If the voltage on the Follow jack is greater than the envelope voltage, the envelope will
rise; if the voltage on the Follow jack is less than the envelope voltage, the envelope will fall.
That is, the envelope will always "seek" the Follow signal: it will go up if the Follow signal is higher,
and it will go down if the Follow signal is lower. This is where the term "follow" originates.
Rule 2: The envelope can only rise and fall at the speed set by the Rise/Fall controls and CV.
This means that if the Follow jack suddenly jumps up (for example, when a gate is applied), the
envelope will try to follow that jump by rising, but it can only rise as fast as the controls allow it. The rate
of change, or slew, is limited, thus we call the Follow circuit a "slew limiter".
Note that the term "envelope voltage" in Rule 1 refers to the internal envelope voltage, before the Env.
Level slider and Env jack output driver. Internally, the envelope has a maximum of 5V and minimum of
0V, which is why the Follow jack only responds to voltages from 0V to 5V. The Env jack's output driver
doubles the internal voltage, so a 5V internal envelope corresponds to approximately 10V envelope on
the jack.
Armed with these two basic rules, we can now showcase some advanced uses for the Follow jack in
the following sections.
Creating ASR and ADSR Envelopes
Cycle off
Rise/Fall
sliders and
switches to
taste
Gate signal
Rise CV
(CV/Gate
keyboard, or
sequencer with
gate width
Trigger
control)
From sound
Follow
source
To mixer/
output amp
Slow
Med
Fast
Cycle
Slow
Fast
Rise
Fall
Env. Level
Fall CV
Time CV
Env
Cycle
EOR
Audio
In
Out
EnvVCA
ASR Envelope
An ASR (attack-sustain-release) envelope is trapezoidal,
with a rising slope (attack), a flat plateau (sustain), and a
falling slope (release). See Figure 7. The width of the
sustain stage is controlled by the width of the gate input:
holding the gate high longer results in more sustain. This is
in contrast to an AR (attack-release) envelope, which is the
triangular shape that results from patching into the Trigger
jack or using the Cycle button.
Patch the gate output of a CV/Gate keyboard to the Follow
jack and the Trigger jack, using a mult or stacking cable.
Patch an audio sound source into the Audio In jack, and
run the Audio Out jack to a mixer or amp.
If using a keyboard as a gate signal, tapping a key quickly
will result in a staccato note, while holding the key down
longer will result in a longer note. Keep in mind that the
minimum note length will always be determined by the rise
and fall time parameters, no matter how short the gate
input is.
Instead of a CV/Gate keyboard, you could also use the
gate output of a sequencer that has control over the gate
length (pulse width). Setting longer gate lengths for certain
notes will emphasize or accent them in the sequence.
This patch works because we patched the gate into both
the Trigger and Follow jacks. The Trigger jack ensures a
complete envelope will output even if the gate width is very
short. The Follow jack produces the sustain. If we had just
patched a gate into the Trigger jack, the envelope would
start to fall once the peak is reached and we would have
no sustain. However, if the gate at the Follow input is still
high, the envelope will remain high, creating the sustain
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