10.6

705Logic Pro Instruments
In a modular synthesizer, signal routing is achieved by physically cabling modules to
each other. In most modern synthesizers the signal routing between modules is internally
prewired and is typically changed using switches, knobs, and other controls.
For a discussion of synthesizer components and their interaction with each other to control
and shape sound, see How subtractive synthesizers work.
Synthesizers have existed far longer than you might imagine. In the days that preceded
the use of digital technology, all electronic synthesizers were analog. Prior to the use of
electricity, synthesizers were mechanical. There are significant differences between analog
and digital synthesizers:
• Analog: An analog synthesizer combines voltage-controlled circuits—such as
oscillators, filters, and amplifiers—to generate and shape sounds. The amount of
voltage is typically related directly to the waveform pitch, with higher voltages equaling
higher pitches.
• Digital: 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.
• Hybrid analog and digital synthesizers: Some synthesizer designs feature digital
oscillators that generate signals—using binary descriptions of waveforms. The digital
oscillator signal is then sent to analog filters and amplifiers. The main advantage of this
approach is that digital oscillators don’t drift in pitch, which is a common problem in
analog oscillators.
• Virtual analog: A virtual analog synthesizer is a digital synthesizer that mimics the
architecture, features, and peculiarities of an analog synthesizer. The behaviors and
functions of the oscillators, filters, and other modules that you would find in an analog
synthesizer are emulated by computer algorithms.
ES1 is a virtual analog synthesizer. Its virtual signal flow is that of a typical analog
synthesizer, but all components and signal processing—the virtual oscillators, filters, and
so on—are calculated by the central processing unit (CPU) of your computer.
ES1 emulates some of the idiosyncrasies of particular analog circuits—in cases where
they tend to sound nice—such as high oscillator levels overdriving the filter. Other analog
synthesizer phenomena, such as slowly drifting out of tune (as the instrument heats up),
are not simulated. See Logic Pro ES1 overview.
Virtual analog synthesizers have other advantages over their analog counterparts as
well. They are programmable, which means that you can save sound settings; they can
be automated, so you can record and play back fader and knob movements; and they are
often multitimbral, which allows you to play different sounds at the same time, on different
instrument channels. Aspects such as polyphony—the ability to play multiple notes—and
velocity sensitivity are found in most virtual analog synthesizers but in very few analog
instruments.