Voltage Control

As you can see an oscillator produces a sound and with various different waveforms that it can output. It can produce a few different sounds already but one of the main ingredients of being able to use various synthesiser modules together is the ability of voltage control. It’s what enables the modules to be linked together in interesting ways. For instance on the oscillator which we have just looked at the pitch can be altered by applying a voltage to its input. This is why the humble oscillator became known as the “voltage controlled oscillator” in synthesiser modules.

If you applied a voltage to the “voltage controlled input” of the oscillator it would produce a certain pitch so you can make the oscillator produce certain frequencies by applying a certain voltage to the input of the oscillator .To make it logical the higher the control voltage that you apply the higher the pitch the oscillator produces. This might not in isolation sound like much to get excited about through but as we start to introduce more modules and the way they interconnect you will start to see the overall picture more clearly.

First imagine a keyboard, not a computer keyboard but a musical keyboard like that of a piano. Now image if it was wired to produce a different voltage for every key that was pressed. You could control the frequency or pitch of the oscillator! It’s actually not that difficult to do and that’s how the first generation of synthesisers were controlled or played. (You’ll see later why the words controlled and played become slightly blurred!) they had a line of resistors in series with each other and a voltage applied across them, them each key tapped into a particular part of this resistor ladder and produced the required voltage.

When I say required voltage I refer to the voltage needed to make the keys produce the same frequencies or notes as that of a piano, incidentally one of the most popular “systems” for keyboards and oscillators was the one volt per octave system, where basically if you remember your theory from the music lessons you had at school a piano keyboard is made up of notes that make up an octave, so for instance if you played an “A” note on a synthesiser keyboard it would for instance output a voltage of one volt for simplicity sake. If you then played the “A” note an octave higher then two volts would be output. A third “A” up would produce three volts and so on.

I say system because in reality it wouldn’t make much difference what the voltages produced were as long as they made the oscillator play the right pitch .Well that’s quite correct in isolation but what if you wanted one keyboard to control two oscillators at the same time or you wanted something else to control the oscillators frequency!

That’s why it was important to use a common voltage method. Later on I’ll cover interfacing synthesisers together, that’s when it starts to get exciting!

Low Frequency Oscillator