Q: "How does my Virtual Analog synth differ from an "actual" analog synth?"
A: Analog synthesizers have existed for more than 125 years (Go to http://www.obsolete.com/120_years/ and read about Elisha Grey's 1876 "Musical Telegraph"). The term "analog" applies both to signals and the devices that generate or process them. A microphone is the ultimate analog device. It receives fluctuations in sound pressure levels. In response, it emits corresponding fluctuations in electrical voltage. If you were to plot both sound pressure and voltage variations on a chart, the graphs would look very similar (remember, the signal from the mic is voltage, not sound). The voltage signal is a representation, or analogy of, the original sound. That's really all the word analog means.
An analog synthesizer uses voltage controlled analog modules to synthesize sound. The three main modules are: Voltage Controlled Oscillator (VCO), Voltage Controlled Filter (VCF), and Voltage Controlled Amplifier (VCA). The oscillator generates a periodic waveform, the filter usually employed removes certain frequencies from the waveform, and the amp varies the attack and decay characteristics These variations in voltage move directly and continuously, flowing smoothly in an infinite continuum. In the analog world, even stepped waveforms such as square waves move continuously. So analog signals have two key properties: (1) they represent changes in voltage, and (2) their parameters - frequency, amplitude, etc. - can be continuously variable.
In contrast, digital synthesizers represent signals as numbers. Digital signals are quantized into a finite number of discrete steps, and there are no levels between each step. 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 analog's infinite resolution.
A Virtual Analog synthesizer is all digital (or uses digital circuitry to control analog components). It emulates analog characteristics by implementing mathematical models of analog circuitry. Analog modeling is a type of physical modeling, which imitates electronic hardware. Software synths that employ analog modeling include BitHeadz's Unity AS-1, Native Instruments' Reaktor and the Access Virus Indigo. Hardware analog modeling devices include the Access Virus C, Clavia Nord Lead and Korg MS2000 synths. Other Virtual Analog devices, such as the Line 6 Pod, model tube amps, speaker cabinets, and spring reverbs.
So, can you hear the difference between an analog synth and its digital virtual model? The answer, though purely subjective, is often "Yes, but..." Some players long for the "bite" of Moog filters on bass lines, or the unavoidable "clipped" sound of an ARP 2600. Others see the improved controllability of virtual synths as a refinement that gives them more sound-shaping power. As with all technological advances in music, the only thing that really matters is how it sounds to you! As digital systems continue to improve the differences in sound between an analog device and a digital device trying to emulate it become ever harder to discern. Of course digital devices can go places that would never be possible with analog.
