Synthesizer - Types of Synthesis

Types of Synthesis

Additive synthesis builds sounds by adding together waveforms (which are usually harmonically related). An early analog example of an additive synthesizer is the Teleharmonium and Hammond organ. To implement real-time additive synthesis, wavetable synthesis is useful for reducing required hardware/processing power, and is commonly used in low-end MIDI instruments (such as educational keyboards) and low-end sound cards.

Subtractive synthesis is based on filtering harmonically rich waveforms. Due to its simplicity, it is the basis of early synthesizers such as the Moog synthesizer. Subtractive synthesizers use a simple acoustic model that assumes an instrument can be approximated by a simple signal generator (producing sawtooth waves, square waves, etc.) followed by a filter. The combination of simple modulation routings (such as pulse width modulation and oscillator sync), along with the physically unrealistic lowpass filters, is responsible for the "classic synthesizer" sound commonly associated with "analog synthesis" and often mistakenly used when referring to software synthesizers using subtractive synthesis.

FM synthesis (frequency modulation synthesis) is a process that usually involves the use of at least two signal generators (sine-wave oscillators, commonly referred to as "operators" in FM-only synthesizers) to create and modify a voice. Often, this is done through the analog or digital generation of a signal that modulates the tonal and amplitude characteristics of a base carrier signal. FM synthesis was pioneered by John Chowning, who patented the idea and sold it to Yamaha. Unlike the exponential relationship between voltage-in-to-frequency-out and multiple waveforms in classical 1-volt-per-octave synthesizer oscillators, Chowning-style FM synthesis uses a linear voltage-in-to-frequency-out relationship and sine-wave oscillators. The resulting complex waveform may have many component frequencies, and there is no requirement that they all bear a harmonic relationship. Sophisticated FM synths such as the Yamaha DX-7 series can have 6 operators per voice; some synths with FM can also often use filters and variable amplifier types to alter the signal's characteristics into a sonic voice that either roughly imitates acoustic instruments or creates sounds that are unique. FM synthesis is especially valuable for metallic or clangorous noises such as bells, cymbals, or other percussion.

Phase distortion synthesis is a method implemented on Casio CZ synthesizers. It is quite similar to FM synthesis but avoids infringing on the Chowning FM patent. Also it should be categorized to modulation synthesis along with FM synthesis, and also to distortion synthesis along with waveshaping synthesis, and discrete summation formulas.

Granular synthesis is a type of synthesis based on manipulating very small sample slices.

Physical modelling synthesis is the synthesis of sound by using a set of equations and algorithms to simulate a real instrument, or some other physical source of sound. This involves taking up models of components of musical objects and creating systems that define action, filters, envelopes and other parameters over time. The definition of such instruments is virtually limitless, as one can combine any given models available with any amount of sources of modulation in terms of pitch, frequency and contour. For example, the model of a violin with characteristics of a pedal steel guitar and perhaps the action of piano hammer. When an initial set of parameters is run through the physical simulation, the simulated sound is generated. Although physical modeling was not a new concept in acoustics and synthesis, it was not until the development of the Karplus-Strong algorithm and the increase in DSP power in the late 1980s that commercial implementations became feasible. Physical modeling on computers gets better and faster with higher processing.

Sample-based synthesis One of the easiest synthesis systems is to record a real instrument as a digitized waveform, and then play back its recordings at different speeds to produce different tones. This is the technique used in "sampling". Most samplers designate a part of the sample for each component of the ADSR envelope, and then repeat that section while changing the volume for that segment of the envelope. This lets the sampler have a persuasively different envelope using the same note. See also Wavetable synthesis, Vector synthesis, etc.

Analysis/resynthesis is a form of synthesis that uses a series of bandpass filters or Fourier transforms to analyze the harmonic content of a sound. The resulting analysis data is then used in a second stage to resynthesize the sound using a band of oscillators. The vocoder, linear predictive coding, and some forms of speech synthesis are based on analysis/resynthesis.