What is a Synthesizer And How Does it Work?

A synthesizer is an electronic music instrument that allows for the processing and manipulation of waveforms generated by oscillators.

The history of synthesizers goes back to the late 19th and early 20th century, which witnessed the development of the first synthesizer-like instruments. Among them are Thaddeus Cahill’s Dynamophone and the Theremin, named after its Russian inventor Leon Theremin. Both instruments were highly influential in the development of synthesizers but were too complex to achieve commercial success.

It took inventors a few more years to develop the first popular electronic instrument, the Hammond organ, released in 1935. It is considered a monumental product in the electronic instruments market. Yet, the term synthesizer was only coined in 1956 to describe the RCA Mark I Synthesizer developed by Harry F. Olson and Herbert Belar. While the Hammond organ was fairly compact, the RCA Mark I and RCA Mark II Sound Synthesizers were massive and expensive, limiting the accessibility of synth-like instruments to the average person.

The next crucial invention, the modular Moog Synthesizer, entered the market in 1964 and essentially paved the way for modern synths. Its developer, Robert Moog, found a way to control pitch through voltage and manipulate it through other components, including envelopes, filters, and sequencers.

The 1970s witnessed the birth of the Minimoog, a small and affordable synthesizer, and other, much more compact synths, such as the ARP 2600. Around that time, the instruments began catching the attention of various artists, particularly in the US and UK. More and more musicians began integrating them into their production process, making synths an essential part of modern music-making.

The 1980s marked the shift from analog to digital, the introduction of digital technologies, and new ways to synchronize electronic music instruments, commonly referred to as MIDI. This transition brought about a host of new possibilities, leading to the release of the Yamaha DX7, the first commercially successful digital frequency modulation (FM) synthesizer. Digital synths remained the preference until the 2000s, during which analog synths regained popularity.

Today, most synthesizers exist as software versions, while many traditional sounds have been integrated into VSTs. But how do analog synths differ from digital ones, and what is the difference between hardware and software synthesizers?

Synthesizers are broadly classified into two categories: analog and digital. Analog ones use analog circuits and signals to generate and manipulate sound. In contrast, digital ones use digital signal processing (DSP) to achieve similar results. Some, however, are described as hybrid. All three fall into the category of hardware synths.

Analog synths can be monophonic (capable of only playing one note at a time) or polyphonic (capable of playing multiple notes simultaneously). They are commonly associated with a warmer sound and allow for easy modification. Because they came before digital synths, they are not always compatible with MIDI and other modern technologies.

Digital synths are commonly polyphonic and come with more options to create sounds in ways that cannot be achieved with analog ones. They allow for different forms of synthesis, including sampling, FM synthesis, or additive synthesis. Lastly, they are capable of preset memory and are usually more affordable.

While hardware synths remain popular, the introduction of digital audio workstations (DAWs) and digitized music technology allowed for the development of software synths and VST instrument plugins. The former are digital versions of the original hardware, while the latter exist to generate audio that resembles synth sounds and usually contains various ‘traditional’ samples.

Synthesizers enable music producers to generate and manipulate a wide range of sounds, including noise and textures. They are usually connected to a (built-in) keyboard and contain several controls that allow for audio synthesis.

At the core of most synths lies the oscillator, a tool capable of generating raw sound in the form of sound waves (saw, square, sine, and triangle waves) and noise. Synths usually contain more than one oscillator, allowing sounds to be combined and layered, and an LFO (low-frequency oscillator). An LFO can further manipulate a sound in various ways and render it more rhythmic, among other things. Some synths, however, use sound samples as raw sounds that can be further processed and manipulated. The pitch of the raw sound is modified by the voltage, with higher levels equaling a higher pitch and vice versa. Meanwhile, the duration and volume of a sound are controlled by an amplifier, which is connected to a so-called envelope.

Envelopes contain four functions that determine the attack, decay, sustain, and release of a note. The attack controls how long it takes for a sound to reach its total volume. The sustain determines the sound level during the time the key is pressed, while the decay determines how long it takes the sound to reach the ‘loudness’ set by the sustain. The release defines the fade-out length, ranging from long and soft to short and sharp. The four parameters give sound designers and producers much control over a sound.

Sounds can be further manipulated by filters, such as hi-pass or low-pass filters. They allow for the removal of frequencies to, for example, make a sound appear placed underwater. Arpeggiators exist to create a repeating sequence of singular notes and create unique, immersive melodic patterns. Producers can determine the duration, speed, octave range, and order of notes, among other things.

Many virtual synthesizers, such as the renowned VST Omnisphere by Spectrasonics, allow further manipulation through built-in effects, including distortion, reverbs, or delays. They also come with many other functions, opening the doors to limitless experimentation.

Additive synthesis requires sound designers to start from scratch. The process begins with generating sounds with oscillators that are then combined, layered, and further modulated by envelopes and filters. Some synths allow for precise modulation by offering control over each wave. In contrast, others revolve around the modulation of sound wave groups.

Subtractive synthesis revolves around filtering out sound parts and frequencies. Various tools and parameters, including envelopes and LFOs, allow for further modulation. This way, sounds can be shaped according to one’s preferences. Subtractive synthesis is popular for its distinct, often warmer sound and because it is less resource-consuming.

As its name suggests, sample-based synthesis revolves around the usage and modulation of preexisting sounds. It is an exciting form of synthesis, as any sound can be used and manipulated. Many VSTs revolve around the usage and modulation of both analog and digital samples.

FM stands for frequency modulation, a complex form of synthesis that revolves around generating sound with so-called operators. Sound designers start by creating a base signal and then modulating it with sounds generated by other operators. The resulting sounds can be further modified by filters and envelopes, creating complex, multidimensional sounds.

Granular synthesis allows designers to break down sounds into tiny grains. It resembles sample-based synthesis, using preexisting sounds to create textures, soundscapes, or constantly evolving sounds. The particles can be layered onto each other and are commonly modulated by time-stretching and pitch-shifting tools.