ER-301/Linear Unipolar VCA

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Applications

  • Modulating the amplitude of a signal without inverting (flipping).
  • Amplitude modulation (AM)
  • Curing VCA bleed when working with envelope generators that have an offset (i.e. do not close completely).
  • Turn oscillators into repeating envelope generators.
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If you already know that your modulating signal is always positive (or always negative) then there is no reason to this unit and instead you should use the Linear Bipolar VCA unit because the rectification operation would just waste CPU cycles.


Description

This unit is used to modulate the amplitude of an incoming arbitrary signal with the rectified version of another signal. This last part in bold is what differentiates this unit from the ER-301/Linear Bipolar VCA unit. Suppose you used a VCA to modulate a 440Hz triangle wave with a 20Hz sine wave. Here is what the result would look like with a bipolar VCA and a unipolar VCA (like this one):

Notice how in the bipolar case, signal is passed through the VCA on both the positive and negative lobes of the sine modulator. However, in the unipolar case, signal is passed only on the positive portions of the sine wave.

VCA Bleed

This unit can be used with envelope generators that do not close all the way. In this case, you would set the level to a small negative value (in the case of a positive envelope) or a small positive value (in the case of a negative envelope) to overcome the envelope's internal offset. Then make sure you are using positive-half rectification for positive envelopes and negative-half rectification for negative envelopes. The rectification will clamp the envelope to zero, thus guaranteeing a fully closed VCA that passes no signal.

Special Menu Operations

Rectify Type

Here you can choose from the 3 available types of rectification: positive-half, negative-half, and full.

For further details on rectification, see ER-301/Rectify.

Parameters

level

Control Type Has Sub-chain? Sub-chain Parameters Fader Scale
Gain/Bias yes gain (-10 to 10)

bias (-5 to 5)

linear


This parameter controls the (pre-rectified) amount by which the incoming signal is multiplied.

pan

Control Type Has Sub-chain? Sub-chain Parameters Fader Scale
Gain/Bias yes gain (-10 to 10)

bias (-1 to 1)

linear


This parameter only shows up when the Mixer Channel is inserted into a stereo chain. The pan amount for the left and right channels follows the behavior depicted in the following graph:

Pan-law.png

In other words, a value of -1 will hard pan to the left, a value of +1 will hard pan to the right, and a value of zero will pan to the center (no attenuation for both channels).