Subtractive Synthesis

One of the earliest sound synthesis methods (specifically for voice) was the vocoder (``voice coder'') [119,118,465]. The vocoder was essentially an electronic ``buzz source'' shaped by a bandpass filter bank (implemented using analog electronic circuits). It is therefore an example of what is called subtractive synthesis in computer music. Since the vocoder was an analog system (at least for the first two decades or so of its use [140]), modern digital phase vocoders may be considered virtual analog systems.

However, the term ``virtual analog'' appears to have originated in the 1990s when digital synthesizers appeared that were designed to simulate earlier analog synthesizers, particularly Moog synthesizers. The first virtual analog synthesizers included the

• Nordlead ``Virtual Analog Synthesizer'', followed by
• Roland ``Analog Modeling Synthesis'', and
• Yamaha ``Analog Physical Modeling'' (AN-1).

Like the vocoder, analog synthesizers were based primarily on subtractive synthesis. The ``buzz sources'' were generally spectrally rich waveforms such as

• sawtooth
• square
• triangle
• pulse-train
• noise

These source waveforms were then passed through filters and other operators. In particular, they could be summed or multiplied together (multiplication being called ``ring modulation'').

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written by Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.