4ms EnvVCA, Руководство пользователя

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Sidechaining (Envelope Following)
The Follow jack can be used to create an envelope that follows an audio signal’s envelope. This
envelope can be inverted and used to control a VCA, creating a “ducking” effect on another sound. This
technique is called sidechaining.
A common application is to use a kick drum to duck another sound source, for example, a background
drone. Patch an audio source that’s making a kick drum sound into the Follow jack of Channel B. Make
sure Cycle is off. Start with the switches at Med , the Rise slider all the way down, and the Fall slider in
the center. If you turn Level up, the Env Out B jack will be outputting an envelope that roughly follows
the kick drum’s envelope. Adjusting Rise and Fall will control the attack and release of the envelope,
that is, how quickly the envelope responds to the attack and release of the kick drum.
For this example we want to invert the envelope, so turn Level all the way counter-clockwise, and turn
Offset to around 2:00. Env Out B will now be outputting an inverted envelope that rests at about 5V
and then ducks down when the kick drum plays. Patch this inverted envelope into Channel A’s VCA CV
jack. Run the audio that you want to be ducked (e.g. a drone sound) into Channel A’s Audio In , and
listen to the output on Audio Out . You should hear the drone play at normal volume, and then briefly
get more quiet whenever the kick drum fires. Try listening to the drone and the kick drum
simultaneously to get the full effect.
Adjust Channel B’s Rise and Fall sliders to control how quickly the envelope responds. If the sliders
are set too fast, the envelope will trace the individual peaks of the sound wave, not the overall
envelope, and the result will be like a subtle AM effect. If the sliders are set too slow, the volume won’t
change much when the kick drum fires.
You can also adjust Channel B’s Offset and Level knobs to control the dynamic range of the ducking. If
you want less ducking, turn Level towards center to reduce the amplitude of the envelope. On the other
hand, if the kick drum is quiet you may need to turn Level towards the extreme counter-clockwise
position to generate an envelope with enough amplitude to get the amount of ducking you want. Offset
almost always needs to be between 1:00 and 3:00. If it’s too low, the output will be too quiet, and if it’s
too high, the output will be at maximum volume with very little ducking.
Audio Filter
The Follow jack can be used as an exotic audio low-pass filter by taking advantage of its slew-limiting
properties. First, the audio signal must be shifted up such that it’s within the range of 0V to 5V. Typically
a level shifter can be used to add the required DC offset. You may also need to attenuate the audio so
that it’s no more than 5V. Any signal outside this range will be clipped, resulting in harsh distortion.
Patch this adjusted audio into the Follow jack. Patch the Env Out jack to your mixer/amp. Turn Level
all the way up and turn Offset to center. To start, set the Rise / Fall sliders and switches to the fastest
positions. Send a steady positive voltage into the Time CV jack and turn the Rise CV and Fall CV
knobs all the way down.
At this point you should be hearing an audio signal that is similar to the original signal.
Now make the rise and fall times slower by adjusting the Rise/Fall CV knobs and sliders, or by
adjusting the CV patched into the Time CV jack. As you do this, you should hear the audio get more
muffled, as the slew becomes limited and higher frequencies can no longer pass.
To make more exotic sounds, try just adjusting the rise or the fall time. This will let the rising portions
and falling portions of higher frequencies pass differently, creating some unique harmonics.
Waveshaper
By limiting the slew, wave shapes with sharper transitions can be altered to have smoother transitions.
For instance, feeding a square wave into the Follow jack will produce a trapezoidal or triangular wave
on the Env Out jack. Adjust the Rise/Fall sliders and switches to get a maximum amplitude output
waveform while still performing the desired amount of waveshaping. These controls will need to be re-
adjusted if the frequency of the waveform changes. You may be able to use the Time CV jack and
Rise/Fall CV knobs to track the frequency and create a somewhat consistent variable-frequency wave
shaper.
Portamento/Glide
The output of a CV/Gate keyboard or a sequencer is often a step-wave, meaning that the voltage jumps
(or “steps”) from one voltage to the next as the notes are played. When this is patched into a VCO, the
result is a sequence of notes that jump from one pitch to the next. Adding in some slew causes the
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