# VCA.MTH.1

Lesson Summary

Define and formulate amplitude in decibels (dB).

Vocabulary

Amplitude -  The maximum absolute value of the signal. Designated by an uppercase A. Pascal - the SI derived unit of pressure. Designated by Pa.

Decibel - A logarithmic unit used to express the ratio between two values of a physical quantity. Decibel is commonly used in acoustics as a unit of sound pressure referencing a pressure of 20 micropascals. Designated by a dB.  Exercise

Add a volume knob to the Werkstatt.

Materials 1 x 10kΩ Potentiometer Jumper Cables 1 x AA Battery Holder
Hardware

We will be adding a volume knob to work with our Werkstatt.  This knob will change the dB output of our Werkstatt.  First we will need to match the settings to Figure 1.   This will give us a constant Sawtooth wave to experiment with. Figure 1. Sawtooth wave VCA MODE ON

When our Werkstatt VCA is set to to MODE ON we get a constant tone.  This also means that our VCA IN pin can accept a voltage from -2.5 to +2.5 V.  To create a volume control we will need a negative voltage.  To do this we simply connect our battery backwards.  A battery pack has two leads, one red (positive) and one black (ground).  By simply swapping these two leads we will be able to get a -3V from our two AA batteries.  We then pass this -3V through our 10kΩ potentiometer to give us a variable control over how much of that voltage is passed on to the VCA IN.  Observe Figure 2 for a detailed visual diagram.

Figure 2. Volume control Werkstatt modification.

Now you will notice as we turn the volume knob the output of our Werkstatt is changed.  If we were to use the + voltage from our battery our volume would only ever get louder, never quieter.

If we switch our VCA MODE to EG instead of ON you will hear that the change is much less noticeable.  This is because the VCA IN can now accept -5V - +5V as a control voltage.  We could make a similar volume knob by simply doubling our AA batteries to get closer to a -5V.

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