Does Voltage Make a Sound?
Let's start at zero volts with an Analog Modular Synthesizer Summary.
An analog synthesizer is a physical instrument that converts voltage into a sound signal. That is the magic of audio synthesis.
An analog synthesizer is a sum of parts. These parts are modules, hence the term "modular synthesizer."
Modular synthesizer modules are standalone units that are collected and provided power in a don't do anything until you connect them together and you provide power in a box/case/skiff/eurorack rack. "Patch Cables" are 3.5mm mono cables that serve as a bridge for signal to travel from one module to another module. In closing, if modules are not wired together with patch cables, nothing will happen.
Semi-Modular Synthesizers
An all-in-one powered synthesizer is called semi-modular. The advantage is that modules are pre-wired. This reduces the need for external wiring with patch cables. The synthesizer is semi-modular if it has open mini-jacks or a patchbay of mini-jacks that allow you to rewire the signal.
Rewiring means you can send and receive signals from external devices. This can be a controller device like a keyboard controller or an analog step sequencer, which can repeat a number of notes, or steps. The keyboard and step sequencer transmit control voltage signals and gate/trigger signals.
So, does voltage make a sound? Depends. Control voltage and gate/trigger signals are voltage generated by a controller. Hence, control voltage. This is silent.
Oscillators: VCO and LFO
Sound is generated by an oscillator. An oscillator generates waveshapes. Whether or not you can hear an oscillator depends on the voltage reaching the oscillator.
Frequency
The range of human hearing is 20Hz to 20,000 Hz. Below 20Hz and above 20,000 Hz is said to be inaudible.
Oscillators can run the range of frequencies. A Low Frequency Oscillator, or LFO, is inaudible until you turn the dial full right. This low frequency takes advantage of waveshapes.
For example, a square waveshape is high, low, or on/off/on/off. A square LFO can be used to modulate other modules. Basically, you wire the LFO to send signal to a control dial. The LFO rate is turning the dial high/low, high/low, so you don't have to.
In review, a Modular Synthesizer is constructed of modules. A semi-modular synthesizer is pre-wired, with open jacks for you to connect external devices. A keyboard controller or step sequencer will send controlling voltage to a synthesizer. A controller's control voltage is silent.
Audio is Control Voltage
This is the fun stuff. An LFO signal is a low-frequency audio signal. Audio connected to a control voltage input will modulate that control dial. Low frequency means you can hear a sudden high/low change, or a rise between high and low signal.
A Modular Synthesizer is best when its modules can be modulated.
I'm a semi-modular fan. I have an ice tray repurposed as a modular rack for six modules. This requires a lot of patch cables. Getting the two to play together depends on the semi-modular instrument. Some are a closed audio system that allow control voltage in. Others may be really open. But it's the pre-wiring that can get confusing when you get started with analog synthesizers.
In closing, analog synthesizers are a great instrument for creating unique sounds. Just know that controller signals are also known as control voltage. And a keyboard or sequencer controller sends voltage signals that are labelled as control voltage or gate signals. Both are silent. Both are capable of changing sound in magical ways.
The oscillator frequency, or pitch, is voltage controlled. This kind of oscillator is a VCO, or voltage controlled oscillator. It can be changed with voltage, as well,
can generate an audio signal and filter out frequencies and make the sound louder and quieter by using voltage.
The signals traveling through a synthesizer are audio signals and control voltage, or CV. The key thing is that audio signal has energy. An audio signal's amplitude can serve as control voltage.
You are working with audio signal and voltage signals.
Voltage alone doesn't create sound. Signals travelling in a synthesizer are audio signals or voltage that can change, or modulate, dial controls.
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