What is virtual analog synthesis?
Virtual analog synthesis recreates the sound and behaviour of analog synthesizers in software. It models the circuits that gave classic synthesizers their sound, the oscillators, filters, amplifiers and envelopes, along with the small imperfections that make them feel alive.
How it works
A virtual analog synthesizer follows the same signal path as the analog instruments it draws on, an approach known as subtractive synthesis. It starts with waveforms rich in harmonics and shapes them by taking frequencies away.
- Oscillators generate the raw tone. Sawtooth, square and pulse waves are rich in harmonics, triangle and sine waves have fewer, and noise has every frequency at once.
- A mixer blends the oscillators, often with one tuned slightly against another for a thicker sound.
- A filter removes part of the spectrum. A low-pass filter darkens the sound as its cutoff falls, and its resonance emphasises the frequencies around the cutoff.
- An amplifier sets the level of each note.
- Envelopes and LFOs move all of these over time. An envelope shapes each note through its attack, decay, sustain and release, and a low-frequency oscillator adds vibrato, tremolo and sweeps.
Analog circuits are imperfect in ways that matter musically. Their oscillators drift slightly in pitch, their filters respond differently as they’re driven harder, and no two notes come out quite the same. Good virtual analog design models that behaviour, and overcomes problems that belong to digital audio, such as aliasing, the harsh tones that appear when a waveform’s harmonics go beyond what the sample rate can carry.
What it sounds like
Virtual analog gives you the warm pads, fat basslines, cutting leads, brass and plucks of classic synthesizer music, and the squelch of a resonant filter sweeping through an acid bassline. Its controls map directly to what you hear, which makes it the place many people first learn synthesis.
Modern virtual analog instruments go further than the hardware they draw on, with more voices, true stereo synthesis, more filter types and modulation that would once have needed a room full of equipment.
Key terms
- Oscillator
- The source of a synthesizer’s tone, which produces a repeating waveform at the pitch you play.
- Subtractive synthesis
- Shaping a sound rich in harmonics by filtering frequencies away.
- Cutoff
- The frequency at which a filter starts to remove sound.
- Resonance
- A boost at the filter’s cutoff that adds emphasis and, at high settings, a ringing tone of its own.
- Envelope
- A shape that changes a parameter over the course of a note, usually in attack, decay, sustain and release stages.
- LFO
- A low-frequency oscillator, too slow to hear as a pitch, that moves other parameters in cycles.
- Aliasing
- Unwanted tones that appear when digital audio tries to carry frequencies above half its sample rate.
In The Plasma Star
The Plasma Star is Xionia Audio’s virtual analog synthesizer. It brings classic analog character, expansive stereo synthesis and vast sound-shaping freedom together in one instrument, from its oscillators and filters to Motion Waves on every supported parameter.