Anyone who has seen the award-winning, science fiction series ‘Stranger Things’ will have observed the soundtrack is dominated by synth sounds of the 80s. Canadian group Survive composed the soundtrack almost exclusively using vintage ‘subtractive’ synthesizers (e.g. Korg Mono/Poly, Sequential Circuits Prophet-5, Roland SH-101).
So what exactly is a subtractive synthesizer?
Subtractive synthesis is arguably the most commonly used form of synthesis in modern music. The best analogy for how the sound is shaped is to think of a block of stone a sculptor chips away at to arrive at their desired shape. Depending on the artist’s choices the outcome can be extremely varied.
With a subtractive synth you commence with one or more oscillators creating a raw sound (saw, sine, square are examples of the waveforms an oscillator can produce). From there you have a myriad of choices in terms of modifying the sound but an obvious technique is to adjust the filter cut-off. As with our sculptor analogy, reducing the filter cut-off removes some of the audio signal and can transform our bright, raw sound into something more smooth and mellow.
Now if we delve deeper, most subtractive synths have a ‘low frequency oscillator’ (LFO) we can assign to the filter cut-off. It’s low frequency because, generally speaking, the oscillator is below our level of hearing and is used for modifying the output of the oscillator/s that do produce a sound.
Just as the name suggests, the LFO ‘oscillates’ up and down (think of a series of waves in the ocean rippling in succession) and, if assigned to the filter cut-off, will cause our waveform to cycle between the raw, bright sound and more mellow, softer tone. The ‘wob’ bass sound in dubstep is an extreme example of this particular technique.
If you’ve stuck it out this far, chances are you may be interested in trying to create your own sounds using a subtractive synth. The good news is The Edge’s Digital Media Lab provides free access to music production software such as Logic Pro X (you can even borrow a midi keyboard and headphones). Within Logic Pro X there are several ‘virtual analogue’/digital emulations of a subtractive synth such as ‘Retro Synth’.
In addition to The Edge’s Media Lab, State Library offers free access to Lynda.com (a comprehensive video tutorial site) that has a number of courses covering the fundamentals of synthesis and electronic music production. Producing Electronic Music in Logic Pro is well worth checking out.