Filters explored

A VA synth’s timbre lives or dies by its filter. Let’s go deeper… The main way to shape oscillator timbre is by removing frequency content via the filter. Like the classic analogue synths many emulations are based on, filter circuit models’ timbres vary by instrument, and massively impact sound. Measured in dBs/octave, a filter’s slope value refers to steepness of attenuation, a big factor in character. Moog-style filters (generally 24dB/oct) are aggressive and weighty – perfect for bass – and can be overdriven for more beef. Roland-style filters, meanwhile, are often 18dB/oct, and more smooth and ‘rubbery’. Then there’s the Korg MS-20’s dual filters – a 6dB/oct high-pass and 12dB/oct low-pass – which impart a delicious ‘howling’ when resonance is cranked.

Keytracking

Apply a low-pass filter to a synth tone, and higher notes will sound duller and quieter than lower notes. To counteract this, VA synths allow you to dial in filter keytracking. With this applied, the higher the notes you play on the keyboard, the more the filter will open.

Multimode or dual

Modern VA synths usually feature a multimode filter, which means you can switch it between different types – low-pass, high-pass, band-pass, notch, and so on. Many different slope values and styles are often available. Others even give you dual filters for more custom tone-shaping.

Self-oscillating

Many classic filters impart pleasing overdrive or saturation, and VA plugins often emulate this, with a Drive control. Similarly, many filters output an audible sine tone when resonance is cranked right up, which can be tuned with the cutoff frequency knob.