What’s a Synthesizer?

A synthesizer is an electronic device which creates sounds. Typically, it uses oscillators to create basic sounds, filters to remove parts of the frequency spectrum the oscillator sounds reside in, amplifiers to alter volume, and modulators like envelopes to change parameters over time.

OK, I admit that was a barebones answer, and probably full of weird words. What I just described is the basis for American east-coast subtractive synthesis, which is what most popular synths use. It was created by Robert Moog in the 1960s and fully realised as a standalone synth in the 1970s with the Minimoog, which used 3 oscillators, a mixer, a filter, and amplifier, and two envelope generators, and allowed routing of oscillator 3 to oscillator 1 and/or the filter, as well as allowing oscillator 3 to run at sub-audio frequencies for modulation purposes. I will describe these in further detail in the next section. This design came out around the same time as Don Buchla, who was working independently of any Moog influence to create his own modular synthesizer, released his Music Easel, which was the west coast’s idea of the Minimoog: one oscillator modulating another’s frequency or amplitude, which fed into a waveshaper, then low-pass gate (combination lowpass filter and amplifier), with envelopes and a sequencer on-board controlling parameters over time.

Ultimately, the east-coast design reigned supreme, gaining international standardisation. Every major and minor commercially available synthesizer you can think of most likely has an east-coast design layout (VCO+VCO->VCF->VCA) instead of west-coast (VCO->VCO->WS->LPG). Now, let’s talk about what those parts actually are.

Oscillators make noise via a constant waveform repeated indefinitely at a set frequency. It’s often called an Osc for short, or VCO for voltage-controlled oscillator. Many analogue synths only have 4 waveforms: saw, triangle, sine, and square. Saw waves look like the teeth of a saw blade, produce both even and odd harmonics reducing by approximately 6db/octave, and are regularly used as the core of analog oscillator designs. Triangle waves look like equilateral triangles, produce only odd harmonics reducing by approximately 24db/octave, and are also used for analog VCO designs. Sine waves look like a sinusoidal graph, produce a single harmonic, and are the cleanest waveforms. Square waves look like, well, squares, produce only odd harmonics reducing by approximately 6db/octave, and are the only waveform regularly capable of changing its shape and thus sound via pulse width modulation. You can typically modulate an oscillator’s frequency, and syncronise it to another oscillator.

Filters, as the name implies, filter out, or remove, certain frequencies. It’s often called a VCF, or voltage-controlled filter. Four filter types are common: lowpass, which only passes low frequencies/filters out high frequencies, and is the most common; highpass, which only passes high frequencies/filters out low frequencies; bandpass, which only passes a band of frequencies/filters out frequencies higher and lower than that band; and notch, which only passes high and low frequencies/filters out a band of frequencies. Where the filter cuts off frequencies is called the cutoff frequency, and is usually the parameter you modulate. How much emphasis the filter places around the cutoff frequency, or where a peak forms at the cutoff frequency, is determined by resonance, or feedback.

The amplifier, as with audio systems, controls volume. It’s often called a VCA, or voltage controlled amplifier, though it’s often more correct to call it a voltage controlled attenuator, as it simply attenuates the signal (makes it quieter) rather than amplifying (making it louder). It often has no direct controls; rather, you control the envelope associated with it to shape the volume of a sound.

Envelopes, sometimes called contours, transients, and often with the word ‘generator’ appended to each, create a signal which modulated elements follow. It often has 4 stages: attack is the amount of time it takes from keypress to full signal level, decay is the amount of time it takes from full signal level to the sustain level, which is where the voltage stays until you release the key, at which point the release control sets time from the sustain level to zero. It’s common for synthesizers to remove some stages: the Minimoog only had attack, decay, and sustain, with the option to use decay as release. Buchla used Attack-Decay envelopes, where decay and release were combined. Sometimes you’ll see attack-release envelopes, which are similar to AD envelopes but have a hidden sustain stage, controlled by modulation amount. You’ll also see multi-stage envelopes, such as 6- or 8-stage envelopes, which can add hold, or delay, stages, and repeat stages like decay, attack, and sustain. Decay-only envelopes, created by only having decay and/or release active and setting attack and sustain to zero, are very common for percussive sounds and basses.

LFOs are similar to oscillators, but specifically are low-frequency oscillators, with low typically being sub-audio frequencies, often below 2Hz. They’re used for automatic, cyclic modulations, such as old-school dubstep wobble basses when used on filters, vibrato when used on oscillators, and tremolo/leslie effects when used with amplifiers.

Using these in combination spawned hundreds of different synthesizers and classic synthesizer sounds. This article has only discussed subtractive synthesis methods so far, but there are SO many others which I’ll discuss in a future article.