How does a synthesiser work?

Synthesisers have come a long way from their beginnings as bulky, experimental devices to their current status as essential instruments in modern music production. Their ability to generate a wide range of sounds, from realistic imitations of instruments to completely new timbres, has revolutionised the way we think about composition and performance. This article will explore the basic elements of synthesiser sound design – oscillators, filters and modulation – explaining how these components work together to create the sounds that underpin much of today’s music, including innovative approaches to classical compositions.

In essence, a synthesiser is an electronic instrument designed to produce and shape sound. Unlike traditional acoustic instruments, which rely on physical vibrations (such as strings or air columns), synthesisers generate sound electronically. This digital or analogue sound processing starts with a raw tone produced by oscillators, which is then shaped by filters and animated with various forms of modulation. Understanding these components is essential for unlocking the full creative potential of a synthesiser

Oscillators are the main source of sound in a synthesiser. They generate the raw waveforms that serve as the basis for further sound design. These waveforms can be thought of as the ‘ingredients’ that are then mixed and refined to create the final sound.

Each oscillator can produce different types of waveforms, each with their own distinctive characteristics:

Sine waves: Pure single-frequency tones, sine waves produce a smooth, soft sound without additional harmonics. They are often used for bass lines or soft pads.
Square Waves: Known for their rich harmonic content, square waves have a hollow, edgy quality, making them ideal for creating electronic lines or vibrant textures.
Sawtooth Waves: With a bright and jangly quality, sawtooth waves are a staple in many genres, particularly in creating the sharp attack of brass and string synthesised sounds.
Triangular waves: Producing a sound somewhere between sine and square waves, triangular waves offer a softer, more rounded harmonic spectrum.

The frequency of an oscillator determines the pitch of the sound. In a synthesiser, tuning the frequency is similar to tuning a traditional instrument. When multiple oscillators are used together, they can be ‘detuned’ relative to each other to create richer, more complex sounds – a technique widely used to add depth to ensemble pads and leads.

By selecting different waveforms and manipulating their frequencies, sound engineers can generate the raw sonic material that will be further refined. Oscillators set the stage for what’s to come, offering a palette of tones that can evoke anything from a serene ambient atmosphere to an aggressive and ferocious attack. The flexibility of the oscillators is a significant factor in the synthesiser’s appeal, as it allows infinite possibilities for sound creation.

Once the raw sound is produced by the oscillators, filters come into play to shape the timbre and character of the sound. Filters act as dynamic tools for altering the harmonic content of a waveform, allowing sound designers to emphasise or de-emphasise certain frequencies.

There are several types of filters commonly found in synthesizers:

Low-pass filters (LPF): These filters allow frequencies to pass below a certain cutoff point while attenuating higher frequencies. LPFs are widely used to attenuate harsh sounds or to create a warm, rounded tone.
High Pass Filters (HPFs): High Pass Filters, on the other hand, allow frequencies to pass above a set cutoff, attenuating the lower frequencies. This type is useful to remove noise from a sound or to create airy, bright effects.
Band Pass Filters (BPF): Band Pass Filters allow a certain range of frequencies to pass through while attenuating frequencies outside this range. They are excellent for isolating certain harmonics in a sound.
Notch filters: These filters remove a narrow band of frequencies, often used to remove unwanted resonance or reverb from a sound.

Synthesisers in classical music

Although synthesisers are most often associated with electronic and pop music, their influence has infiltrated classical music as well. Contemporary composers of classical music are increasingly exploring the rich sonic palette offered by synthesised sounds, combining traditional orchestral elements with modern electronic textures. This fusion not only challenges conventional notions of classical music but also expands its expressive potential.

Classical composers have traditionally relied on acoustic instruments to create orchestral music. However, synthesisers offer a new dimension of sound design that can complement and enhance these conventional timbres. By integrating synthesizer elements, composers can introduce subtle electronic nuances or even completely new instrumental colours into their works. This approach has led to innovative compositions that bridge the old and the new, demonstrating that synthesised sound can co-exist harmoniously with traditional orchestral instruments.

For classical musicians and composers, synthesisers provide a platform for experimentation. The flexibility of sound design through oscillators, filters and modulation allows the creation of sounds that are impossible with acoustic instruments alone. This opens up a world of creative possibilities, inviting composers to explore textures and dynamics that defy the limits of traditional classical music.

The field of synthesiser technology continues to evolve, with continuous advances in both hardware and software. Today’s synthesizers offer unprecedented levels of control and integration, allowing real-time manipulation of sound parameters that were once fixed in place. The advent of virtual instruments and plug-in synthesizers has made these tools more accessible than ever, democratising the art of sound design for musicians and composers of all genres.

As artificial intelligence and machine learning begin to influence music production, we could see even more sophisticated forms of synthesis emerge. These technologies have the potential to learn from and adapt to a musician’s style, further blurring the boundaries between human creativity and machine precision. Despite these technological changes, the fundamental principles of oscillators, filters and modulation remain at the heart of synthesiser sound design – a testament to their enduring relevance in modern music production.

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