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Synthesizer basics: Oscillator, filter and envelope

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tagsglossar, audio, musik

2 min read

Synthesizer basics: Oscillator, filter and envelope

In short: A synthesizer produces sounds from oscillations: oscillators supply the basic waves, filters shape the sound, envelopes control volume and course, LFOs provide movement.

In more detail: Subtractive synthesis is the classic design (Moog, Prophet, Minimoog, modern software synths): you start with a harmonic-rich sound and filter away what you do not want. Its building blocks apply almost everywhere.

In Depth

Oscillator (VCO)

Generates a waveform with a frequency (pitch):

  • Sine: pure, only the fundamental.
  • Sawtooth: bright, all harmonics (basses, strings, leads).
  • Square/pulse: hollow, odd harmonics; pulse width changes the sound.
  • Triangle: soft.
  • Noise: for hi-hats, wind. Several oscillators slightly detuned sound fat. Octave and fine tuning determine the register.

Filter (VCF)

Shapes the sound by removing frequencies: low-pass (lets lows through, makes it duller), high-pass, band-pass. Parameters: cutoff (cut-off frequency) and resonance (emphasis at the cutoff, “squeaky”). The cutoff movement (for example via an envelope) creates the typical “wah” sound.

Envelope (ADSR) and LFO

The ADSR envelope describes how a parameter (usually volume) changes over time: attack (rise time), decay (fall to the sustain level), sustain (hold level while the key is pressed), release (fade after letting go). Short attack + short release = plucked/percussive, long attack = string/pad sound. An LFO (low frequency oscillator) moves parameters periodically slowly: vibrato (pitch), tremolo (volume), filter wobble.

More types of synthesis and trying out

FM synthesis (Yamaha DX7), wavetable, additive, granular and physical modelling. Effects (reverb, delay, chorus, distortion) round off the sound. For trying out, browser synthesizers and the Web Audio API (OscillatorNode, BiquadFilterNode, GainNode with linearRampToValueAtTime as envelope) are suitable. Learn to work with presets and to change one parameter at a time.

See also: MIDI and DAW, Audio formats, Speech synthesis