Originally posted on Zeros and Ones by Ali Jamieson
Subtractive synthesis is easily the most important type of synthesis you will come across. Why? Because everything that falls under the subtractive umbrella term has gone on to directly influence other types of synthesis such as additive, wavetable, frequency modulation and nearly anything else you can think of.
The term is descriptive as it’s about sculpting sounds from harmonically rich waveforms using filters, envelopes, LFOs and amplitude shaping, and it’s the sound of quite literally thousands of records dating from the sixties right up until now.
Let’s start out by having a look at the front panel of a few common analog synths.
Where better to start than with where it all began – the Minimoog. Released in 1971, this was the first commercially available synthesiser that boasted portability. Previously, synthesisers were huge modular systems confined to the studios of scientists at the BBC Radiophonic Workshop. The Minimoog changed all that – finally keyboardists could compete with their noisy guitar-playing neighbours:
Can’t afford the thousands these go for on eBay now? Not to worry, Arturia make a nifty emulation, the Mini V, which we’re going to look at the front panel of:
I’ve highlighted two key features of subtractive synthesis in red and blue. Let’s start from the left: in red (or pinky red, whatever you want to call it) is our Oscillator Bank.
This section contains anything that generates a tone. We have three oscillators available to us. With oscillator one, we decide the range (synth-speak for octave, not enough time to go into exactly why they use this at the moment) and the waveform (more on these later).
Oscillators two and three can be tuned relative to oscillator one and we can also choose their waveform which, like oscillator one, have triangle, two types of sawtooth and three types of pulse wave.
Next, let’s look at our blue section, which the Moog calls Modifiers. This is the filter stage that uses the famous Moog Ladder Low-Pass Filter. We have cutoff frequency (where in the frequency spectrum our filter begins to do its job) filter emphasis (which you might be more familiar with as resonance or Q) and some envelope function, which we’ll get on to later.
With just these two sections, we can get most of the sounds we want out of the Minimoog – it really is that simple. All synths have a similar signal path – oscillators into a filter into the amp section – so it’s easy to navigate them once you know what you’re looking for.
In 1982, the Japanese company Roland released the now legendary SH-101. A staple workhorse synth in many a studio, the 101 is a monophonic synth known for it’s phat basses and squelchy acid leads:
Costing you around £500 for one in good nick, it’s not an unobtainable piece of gear but the guys atTAL made a free emulation (that sadly isn’t supported anymore) but you can still get from their website.
Like our Minimoog, I’ve highlighted the oscillator section in red and the filter section in blue. Our oscillator section is named VCO, which you might come across in lots of analog synths. VCO stands for voltage-controlled oscillator as many of these machines were pre-MIDI (more on controlled voltage another time).
Our VCO section allows control of range, pitch modulation, the width of our pulse wave and how it can be modulated. Just to the right, highlighted in white is the Source Mixer where we can blend in our other oscillator waveforms: a sawtooth, sub-oscillator (tuned down one or two octaves) and white noise.
The filter section is highlighted in blue as and is named VCF. The quicker among you might have ascertained this stands for voltage-controlled filter. We have the familiar frequency andresonance controls (resonance is amplification of the filter cutoff position, giving a sharp, piercing squeal to the filter at higher values) and Env, Mod and Kbd modulation sliders.
Next, let’s look at the green highlighted section, ENV, our envelope generator. This can be routed to the amplifier and/or the filter, allowing us to shape our sound over time. I’ll cover envelopes in more detail further down the page.
Finally, there’s our Modulator, highlighted in yellow. This is what we may be more familiar with as an LFO, which stands for low-frequency oscillator. Here we can change the rate (frequency/speed) and waveform (sine, triangle, saw, pulse, sample and hold and white noise). We’ll cover most of these terms later on.
By now, you should get getting the idea, so I’ll skip through our last two examples a bit quicker. Next we’ll look at the Korg MS-20, a semi-modular monophonic bassline beast produced from 1978 to 1983 and responsible for Mr. Ozio’s Flat Beat.
The modular aspects of this will be covered another time but let’s skim through the interface. Our oscillator section allows for triangle, sawthooth, pulse and white noise waveforms, with oscillator two having an external input section for processing sounds from the outside world through the filters.
Our filter section in blue has two filters, a high-pass and low-pass filter. The peak rotary is what we know as resonance or Q. Underneath there are modulation options from either the LFOs or envelope generators.
The envelopes are in green: envelope one is a simple AR (attack and release, no sustain stage); and envelope two is a slightly more complex AHDSR (attack, hold, decay, sustain and release). Finally, our LFO (in yellow) has a control to morph between sawtooth, triangle and reverse sawtooth or varying degrees of pulse waves.
The last synth we’ll look at is the monster that is the ARP 2600, another monophonic semi-modular that was in production from 1971 to 1980.
Like the Minimoog, this is emulated by Arturia, and that’s what we’ll have a look at below:
The interface can be a bit disorientating compared to synths with a simpler layout. I’ve highlighted the oscillator, filter, envelope and mixer section – by now this should be ample information to acquaint yourself with it – but don’t worry if it takes longer because half the fun of the 2600 is stumbling across bizarre sci-fi sounds made by haphazardly turning things up and down.
...Waveforms and filters to come!
Written by Ali Jamieson