# VCA.SCI.1

Lesson Summary

Combine information from VCO.SCI.2 and relate amplitude to wave dynamics lesson.

Vocabulary

Wavelength - The distance over which the wave's shape repeats. Determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings. Designated by the Greek letter lambda (λ).

Period - The time over which a wave's shape repeats. Determined in a similar manner as wavelength but in the time domain. It is the reciprocal of frequency and is designated by an uppercase T.  SI unit is the second.

Amplitude -  The maximum absolute value of the signal. Designated by an uppercase A.

Frequency - The number of cycles per unit time.  The SI unit for frequency is hertz (Hz), named after the German physicist Heinrich Hertz; 1 Hz means that an event repeats once per second. Designated by a lowercase f.

Hertz - The unit used to represent frequency (Hz)

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 amplitude of the sound wave output..  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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