Synthesizers II: Basic Voice Architecture
Regardless of the type of synthesizer you are dealing with, most synthesizers are made up of the same basic components: oscillators, filters, and amplifiers. These are the three most essential modules you will be dealing with when crafting a synth voice. These can be further built upon (or modulated with) LFO’s, gates, triggers, envelopes, etc. But as a basic sound, these three are the most essential. We will dive deeper into each one of these with a dedicated post to each, but for now it is essential that we understand the basic signal flow.
These concepts are the same regardless of what format of modular you use, but for this series we will mostly use VCV rack as it is free and easily accessible for most people.
In VCV rack, lets connect an oscillator (or VCO – voltage controlled oscillator) directly to the “ins” on your audio output:
Notice how this is a constant sound that does not stop. We can turn the pitch knob to adjust the pitch, or output different types of waveforms to hear different harmonic content from the same fundamental.
This is what an oscillator is - a constant sound source. What a lot of people don’t realize is that with most synths they are familiar with, fixed architecture synths, there is so much more that goes on with each component and how they interact than they realize. Let’s continue exploring this.
Lets load of a filter module and see how that effects the sound. We are going to use a square wave here due to it’s richer harmonic content but feel free to try the others!
Connect your oscillator to the input of the VCF (voltage controlled filter). You will notice the two outputs on this module are LPF and HPF, or a low pass filter and a high pass filter respectively. The low pass filter allows frequencies below the cutoff frequency (set by the “frequency” knob) to pass through or be heard, and the high pass filter does the same for the frequencies above.
The VCA module, or voltage controlled amplifier, is how we control the volume of a synth voice. Connect the output of the LPF to the input of the VCA and the output of the VCA to the in on your audio output as shown below:
Congratulations, you patched a basic synth voice. Now, turn down the VCA completely, adjust some parameters on the VCO and/or VCF, and turn it back up. This is all the stuff that goes on behind the scenes when you play a fixed architecture synth. Now, it is quite frustrating (and slow!) to need to disable amplfier, adjust the pitch and manually adjust the volume for each note. This is where all of that other stuff we mentioned above come into play, and where modular really shines via the use of control voltages (CV).
For now, get familiar with the basic signal flow of VCO>VCF>VCA. This is a major starting point for patching, and understanding what each of these does is essential to understanding synthesis.