Apple Logic Express 7 - Manual (Page 75)

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Synthesizer Basics
If you are new to synthesizers, you should read this
chapter.
It covers important facts about the synthesizer and explains the difference between
analog, digital and virtual analog synthesizers. Important synthesizer terms such as
cutoff, resonance, envelope, and waveform are also introduced.
Analog and Subtractive
An analog synthesizer signal is an electrical signal, measured in volts. To give you a
brief comparison with a technology you’re probably familiar with, we’ll look at speakers.
The speaker “coils” move when the voltage—amplified by a power amplifier and output
to the speaker—changes. When the voltage rises, the speaker coil moves forward. If the
voltage falls, the speaker coil moves backwards.
In a digital synthesizer, the signal flow is digital. Binary descriptions of the signal (a
string of zeros and ones) are fed from one algorithm to another. This is an important
distinction to make. It is not the signal itself that is fed from a virtual oscillator to a
virtual filter and so on.
A virtual analog synthesizer is a digital synthesizer which mimics the architecture,
features, and peculiarities of an analog synthesizer. It includes the front panel with all
controls, which provides direct access to all sound generation parameters.
Logic’s ES1 is an example of a virtual analog synthesizer. Its virtual signal flow is as per
that found in analog synthesizers. It includes some of the desirable idiosyncrasies of
particular analog circuits—in cases where they tend to sound nice, such as high
oscillator levels overdriving the filter. The ES1 also features a graphical control surface
on your computer screen. Its signal processing (those “virtual” oscillators and so on) is
performed by the central processing unit (CPU) of your computer.