A synthesiser is an electronic instrument that can produce a wide range of sounds. Sound is a form of energy that is produced when air molecules vibrate in and move in a pattern known as a wave. These vibrations reach the human ear, which translates them into sounds. The synthesiser creates vibrations in the form of an electrical signal that is converted into sound through speakers or headphones.
Synthesisers have the ability to speed up or slow down these vibrations, allowing the user to modify and manipulate sounds in a variety of ways. A synthesiser can, therefore, imitate other instruments as well as generate a variety of new tones.
Types of Synthesisers
Synthesisers can be classified according to synthesis method and physical architecture.
Synthesisers Classified by Physical Architecture
The physical architecture of a synthesiser refers to how it is built. There are hardware and software synthesisers, while hardware synthesisers can be split into all-in-one units and modular units.
Hardware synthesisers are real, physical electronic devices featuring circuitry that generates and processes signals. Depending on the type of circuitry used, they can be analogue or digital. In terms of the components that make up a synthesiser, they can be modular or all-in-one.
Analogue vs Digital Synthesisers
Analogue synthesisers use analogue circuits and an analogue computer to create and modify sounds. Analogue signals are represented by different voltage levels in the circuits. The levels are continuously variable, meaning that for every increment in level, there can be another in between, allowing a virtual infinity of levels for analogue signals. The problem with fully analogue synthesisers is that each modification to the signal requires a different circuit, meaning that circuits need to be changed to achieve something different with a signal. However, many users prefer the sound of analogue synthesisers.
Digital synthesisers use a series of numbers to store sounds. Each series matches up to a discrete signal level and when they are converted into an analogue signal, they become sound. Due to memory limitations, it is impossible to store every signal level. Despite this, a sufficient number of levels can be stored for the digital signal to accurately mimic an analogue signal without the human ear being able to perceive a difference between the two.
The advantage digital synthesisers have over their analogue counterparts is that they can be programmed, allowing the user to create new sounds and modify existing ones without changing circuits. Digital units also stay in tune and permit the identical reproduction of sounds repeatedly.
Some synthesisers combine analogue and digital technology, allowing users to take advantage of both worlds. Hybrid synthesisers feature analogue signal paths and digital control circuitry.
Modular vs All-In-One Synthesisers
Synthesisers consist of a wide range of components that have different roles, from creating sounds to controlling how signals are routed. In a modular synthesiser, all the components are separate and usually mounted in a rack. They can be moved around but each module must be connected to the other modules being used via patch cables.
Conversely, all-in-one units have all the components required to generate certain ranges of sounds built into a single case.
Software synthesisers are software programs that exist entirely in a computer. They are designed to try and represent hardware synthesisers as accurately as possible.
Synthesisers Classified by Synthesis Method
The synthesis method refers to how the generated sounds are modified to create new tones.
Additive synthesis involves combining sine waves at different frequencies. Decide the frequencies at which the harmonics should be, and add them to the base sine wave, which creates a new waveform.
Digital synthesisers make it easier to perform additive synthesis because the waves are simply numbers in a computer. To achieve the same results with an analogue synthesiser would require a bulky, expensive unit, as complex sounds are made up of hundreds of sine waves and each wave requires a separate oscillator.
Subtractive synthesis is primarily used by analogue synthesisers. It involves removing various frequencies from a waveform created by an oscillator. A filter is used to remove certain harmonics, which alters the spectral content of the waveform.
The cut-off frequency is one of the main controls on a filter, establishing where the filter will start blocking frequencies. Filters according to where they block frequencies in reference to the cut-off frequency.
Frequencies above the cut-off frequency are removed, leading to sounds that are darker.
Frequencies below the cut-off point are blocked. Sounds seem lighter and clearer.
Blocks everything except a narrow band of frequencies around the cut-off frequency.
A narrow band of frequencies around the cut-off frequency is removed.
Another important control for filters is resonance, which boosts the harmonics at the cut-off frequency.
Frequency Modulation Synthesis
Frequency modulation synthesis or FM synthesis creates completely new frequencies by using one wave to quickly increase or decrease the frequency of another wave. The new frequencies are called sidebands and can appear above or below the frequency being modified. This type of synthesis is highly valuable when modifying metallic sounds, such as those produced by bells, cymbals and, other percussion instruments.
The Yamaha DX-7 series is a good example of sophisticated synthesisers that utilise FM synthesis.
Phase Distortion Synthesis
Phase distortion synthesis is an approach used by Casio CZ synthesisers, which is similar to FM synthesis. However, the latter was patented by John Chowning and Casio had to employ a method that achieved similar results without infringing on the patent.
Most synthesis methods produce waves that repeat at some point, also known as periodic waves. Wavetable synthesis isolates one loop of this repetition in a wave and stores a digital copy of it in a table. It has the ability to save every wave a user would want to create, saving them in separate tables, which can later be loaded and played repeatedly. The advantage is that it requires less memory and processor power.
Sample-based synthesis or sampling doesn’t actually create sounds, but plays back sounds that were previously recorded from somewhere else. These recordings are stored digitally and can be recalled instantly when a key on the synthesis is pressed. Their speed can also be increased and decreased to create different pitches. These waves can be manipulated in a wide variety of ways to achieve the desired sound, including trimming, looping and reversing.
Granular synthesis is based on a similar principle to sampling, but it operates on a micro level. The samples are sliced into small sections of 1 to 50 ms, which are called grains. These small slices can be layered on top of each other, played at different speeds, phases, volumes, and frequencies to create completely new sounds. It is considered quite a complex area and is often used to create more experimental sounds as quite a lot can be achieved with this form of sound synthesis.
Buying a Synthesiser on Ebay
Top purchase a synthesiser on eBay, go to the site’s homepage. In the menu on the left, click on All Categories, which will open up a page with all the available categories. Scroll down to Musical Instruments and click the small arrow labelled More to expand the selection. Click on Pro Audio Equipment, which will open up a new page with a menu on the left of sub-categories. Click on Synthesisers and Sound Modules. Results can be sorted by type, brand, condition, features, and sellers.
Synthesisers are popular electronic instruments due to the variety of sounds they can create and their flexibility. They can be used to mimic any instrument but are more often used to create complex sounds with multiple layers. There are a wide range of synthesisers available, depending on their architecture and the methods used to synthesise sound.