Analogue instruments are all about the electrons. They shuttle actual voltages to and fro. Electricity is hard to tame, and the components inside an analogue instrument or effect are also imprecise - especially those that have been sitting around for a couple of decades - heck, those electronics were a bit of a blunt weapon when they were new!
With today’s computers being the signal processing powerhouses they are, developers now have more than enough CPU cycles available to them to be able to - in theory, at least - perfectly emulate the inconsistencies and irregularities of real analogue oscillators. So how are they doing on that score? Let's compare some oscillator waves and see for ourselves…
Step 1: In order to better understand what makes our favourite vintage synthesisers sound so good, we’ll start right at the beginning of their signal paths - the raw waveforms produced by their oscillators. Here's a basic software-generated sawtooth wave as generated by Audacity.
Step 2: We import our software-generated sawtooth wave into our DAW, where we’ve recorded a sawtooth from an old ARP 2600. If we take a look at both waveforms by zooming in or using an oscilloscope plugin such as s(m)exoscope, we can see that there are some distinct differences between the two. The Audacity wave (top) is perfect, while the ARP’s (bottom) has imperfections at the peaks and troughs.
Step 3: Next, let’s take a look at the sawtooth wave generated by Moog’s venerable Minimoog Model D (a vintage unit, not the recent re-issue). In this case, we see that the polarity of the sawtooth wave is flipped, but that doesn’t matter in the audio range. What does matter is that it has even more pronounced imperfections than the 2600’s sawtooth wave, as can be seen here.
Step 4: Things start to get really interesting when comparing a software-generated square wave with one produced by a vintage analogue synthesiser. Here we’ve got a nearly perfect square wave from Audacity and another, quite imperfect square wave from a Prophet-5. Check out those spiky peaks! Believe it or not, the Prophet-5’s square wave is pretty good, for an analogue synth!
Step 5: Now let’s take a look at the square wave produced by that most cantankerous of synthesisers, the VCS 3 (top). Surprisingly, it looks pretty darned good - it isn’t a near-perfect specimen like that produced by Audacity, but it’ll give the Prophet-5 a run for its money, and it’s far truer than that produced by an original Korg MS-20, as seen in the bottom ’scope.
Step 6: Needless to say, a skilled developer doesn’t simply generate a mathematically perfect waveform and hope we don’t hear a difference. For example, u-he’s clone of Sequential Circuits’ Pro-One, Repro-1, offers up a square wave that shares many of the characteristics of those we’ve seen from vintage gear. That’s Repro-1 on the bottom ’scope, and the Prophet on the top.
Step 7: Similarly, it’s clear that Steinberg did some homework in order to make their Retrologue synth as accurate as possible. Here, we see the sawtooth wave from our original Minimoog on the top ’scope, with the all-but-identical sawtooth from Retrologue displayed on the bottom scope. This is likely as close as one actual Minimoog is to another.
Step 8: Just for kicks, let’s take a look at some square waves from a couple of modern hardware analogue synths to see how they stack up. On top we have a specimen from a Synthesizers.com oscillator, and below, we’ve got a square wave from an Elektron Analog Four. Both exhibit the hallmarks of a well-designed analogue synthesiser with a bit of vintage flavour.