nalog synthesizers, real and emulated, are enjoying renewed popularity today. Indeed, analog devices of all types might be more numerous now than they were during the heyday of ARP, Moog, and Buchla. At the dawn of the 21st century, there is steady demand for the technologies of yesteryear. This article will help you understand some basic analog-synthesis concepts and introduce you to some of the key features of analog synthesizers. Then you’ll be able to better evaluate the analog and pseudoanalog products flooding music stores.

The term analog has nothing to do with resonant filters, ring modulators, or any other widely advertised “analog” features. Vintage analog machines did have these features, but so do digital devices. Analog applies properly to signals and the devices that generate or process them, not to particular synthesizer options.

Analog Defined

FIG. 1: A microphone converts a sound wave into an electrical signal that is analogous to the original sound wave. A graph of air pressure over time for the sound wave looks similar to a graph of voltage over time for the electrical signal.

Consider the quintessential analog device: the microphone. A mic responds to fluctuations in air pressure (that is, sound). It puts out corresponding fluctuations in electrical “pressure” (that is, voltage). If you were to plot both air pressure and voltage variations over time, the graphs would look very similar (see Fig. 1).

The fluctuating voltage at the mic output is a signal, not a sound. The signal is an electronic representation, or analog, of the original sound. That’s all the word analog means—there’s no mystery to it.

Whether it originates in a mic or electronic circuitry, an analog signal represents sound directly and continuously. The voltage does not move in discrete steps from one level to another; it flows smoothly in an infinite continuum of voltage levels. In the analog universe, even stepped waveforms such as square waves move continuously. A square wave’s leading and trailing edges aren’t truly “square.” Examine a square wave closely on an oscilloscope, and you’ll see slightly rounded edges, because the voltage takes a finite time to rise and fall. No physical oscillator can achieve the infinitesimal rise time of the ideal square wave.

Analog signals have two key properties: (1) they are continuous, and (2) their parameters—frequency, amplitude, and phase—are continuously (and infinitely) variable. These properties make analog-synthesizer signals profoundly different from digital synthesizer signals. By definition, digital synths represent signals as numbers. Digital signals are quantized into a finite number of discrete steps, and there are no levels between steps. Likewise, parameter values on a digital synthesizer are quantized into a finite number of steps. Smaller step sizes give a digital synthesizer higher resolution; the higher the resolution, the better the synth can approximate the infinite resolution of analog devices.

Reprinted with permission from Magazine, December, 2000
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