What Is Control Voltage Anyway?
Control Voltage (Often abbreviated to CV) is at it’s most basic a signal which can be applied to an analog circuit to modify it’s behavior. This modification can take many forms but typically with analog synthesis we will be using it to either turn a circuit on and off, or adjust the frequency and intensity of oscillation (which will adjust tone and volume). What makes this interesting is it allows us to modify or control various components of a synthesizer from a separate circuit or device. Probably the easiest example of this would be a basic CV keyboard, When you press a key on the keyboard a DC signal is sent from the keyboard to your synthesizer which tells the synthesizer what note to play and how long to play it. When you press different keys on the keyboard the signal sent will be a slightly different voltage which will modify the synthesizers oscillation, amplifier and envelope to different degrees thus producing different notes and sounds.
Types of Control Voltage
There are three basic types of control voltage which are typically used in analog synthesis, these are as follows:
- Basic Control Voltage – This is what most people think of when they think of CV, This signal typically varies in voltage between 0 and 5 volts (though different manufacturers and makers will use different values) and tells your oscillator what note to play. This is what causes the note played by pressing the high C on a keyboard to be different from what is heard by pressing G for example.
- Gate – Gate is a separate signal which is typically sent directly to an envelope generator or voltage controlled amplifier. Unlike basic control voltage which will vary widely within its range of voltages dependent on the desired notes a gate signal will only have 2 states, On and Off. The gate tells the synthesizer how long a note is meant to be played. Returning to the keyboard example, when you are not touching the keyboard the gate signal will be at 0V or off, when you press a key it will instantly move to its on position at 5V(or the gate voltage for the device you are working with.) The signal will stay on until you remove your finger from the key at which point it will immediately drop back to 0V telling the synthesizer to stop making noise.
- Trigger – Trigger is similar to a gate signal in that it is always in either an on or off position without moving around in between. How it differs from gate is that a trigger signal will turn on and then immediately back off when a key is pressed sending a short pulse to the synthesizer. This pulse is most commonly used to let an envelope generator know when to begin its attack, sustain, decay cycle. The trigger will only send one pulse of a set length and voltage each time a key is pressed regardless of what key is pushed or how long it is held down.
Where Does CV Come From?
There are a myriad of different control voltage devices available which can be controlled and programmed in a variety of different ways. A few common examples which you will often see in synthesizers are as follows :
- Keyboards – Keyboards are the type of controller most of us are most familiar with, Depending on which key is pressed a different voltage level will be sent to the synthesizer causing it to play the note which corresponds with the key pressed. Most keyboards will also output a gate signal which tells the synthesizer how long the key is held down for.
- Low Frequency Oscillators (LFO) – An LFO is an oscillator (similar to the voltage controlled oscillator used to produce sound within a synthesizer) which oscillates at a frequency too low for the sound created to be percieved by human ears. By running the voltage from an LFO into a voltage controlled oscillator you can create a number of interesting effects. For instance if the oscillator operates at an extremely low frequency you can create an up and down sweeping effect through your VCO. Or if you have a higher frequency of oscillation you can create excellent tremolo effects which add vast depth to the sound output by your synthesizer.
- Sequencers – Sequencers are devices which repeatedly switch through a number of steps at a regular (usually adjustable) speed. Each of these steps can have a number of controls to adjust the control voltage they output. These controls often include but are not limited to a switch to deaden the step (makes the synthesizer produce no sound while it is on), course and fine tone adjustments and octave switches. By setting each step you can use these controls to create intricate repeating melodies which will continue to play without requiring you to repeatedly input or play the notes.