Equipment

Synthesizers : electronic organs vs. synthesizers

Organs and additive synthesis

All organs (including acoustic) are based on the principle of additive or Fourier synthesis: Several sine tones are mixed to form a more complex waveform. In the original Hammond organ, built in 1935, these sine waves were generated using revolving tone wheels which induced a current in an electromagnetic pick-up. For every harmonic, there had to be a separate tone wheel. In more modern electronic organs, electronic oscillators serve to produce the sine waves. Organs tend to use fairly simple "formant" filters to effect changes to the oscillator tone--automation and modulation tend to be limited to simple vibrato.

Synthesizers and subtractive synthesis

Most analog synthesizers produce their sound using subtractive synthesis. In this method, a waveform rich in overtones, usually a saw-tooth or pulse wave, is produced by an oscillator. The signal is then passed through filters, which preferentially remove some overtones to obtain a sound which may be an imitation of an acoustical instrument, or may be a unique tonality not existing in acoustical form. An ADSR envelope generator then controls a VCA (voltage controlled amplifier) to give the sound a loudness contour.

Other circuits, such as waveshapers and ring modulators, can change the tonality in non-harmonic ways or create distortion effects which are often not found in natural sound sources. In spite of the popularity of modern digital and software-based synthesizers, the purely analog modular synthesizer still has its proponents, with a number of manufacturers producing modules little different from Moog's 1964 circuit designs, as well as many newer variations.

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