Synthesizers are electronical musical instruments that produce audio signals through several analog and digital methods. The most common techniques include frequency modulation, additive, subtractive, phase distortion, physical modeling, linear arithmetic and sample-based synthesis, as well as analysis/resynthesis. They produce sounds typically shaped and modulated by low-frequency oscillators, filters, and envelopes. Musicians usually play synthesizers with keyboards, both controlled by sequencers via MIDI. Synthesizers are widely popular in film and television soundtracks. 

Synthesizers: Some Examples

As mentioned before, there are several techniques through which synths produce audio signals. Firstly, frequency modulation synthesis (FM) generates sounds by modulating one waveform with the frequency of another. You can use the resulting complex waveform to alter other signals. FM mimicks diverse acoustic sounds. Secondly, additive synthesis generates sounds by combining waveforms into a composite sound. Thirdly, subtractive synthesis creates waveforms by using oscillators and shaping them with filters to boost or eliminate particular frequencies. 

Other examples include phase distortion synthesis. This replaces the analog waveform with complex digital waveforms. In addition, physical modeling synthesis uses a set of equations and algorithms to mimic unique sonic characteristics of musical instruments. Through various steps, the sound realistically approximates the desired instrument. Moreover, the linear arithmetic kind uses PCM samples for the attack of a waveform. Subtractive synthesis is for the rest of the envelope. Furthermore, sample-based synthesis uses a digitally recorded short fragments of a sound taken from an actual musical instrument. When you choose this sound , it plays back at different speeds to create diverse pitches. As a last instance, analysis/resynthesis involves bandpass filters to analyze the harmonic content of a specific sound and resynthesize the sound with a band of oscillators.

How They Work

You can control the sounds that synths create through virtual stages or circuits, such as oscillators, low-frequency oscillators, voltage-controlled filters, envelope generators, as well as voltage-controlled amps

Filters are essential in subtractive synthesis, being the low-pass filter the most common one. Envelopes control the way sounds change over the course of time through several parameters, such as amplitude and pitch. ADSR is the most common envelope, since it includes attack time, decay time, sustain time, and release time. Low-frequency oscillators create electronic signals below 20Hz. Voltage-controlled amps control the volume of the audio signal.