Audio Synthesis Notes

Just a bunch of notes taken while watching a course on Audio Synthesis.

Basic concepts

  • oscillator
  • filter
  • envelope (ADSR, attack, delay, sustain, release)
  • Fourier transform (see 3blue1brown’s video)

Additive synthesis

  • adding sine waves together to make a sound
  • square wave is a specific combination of sine waves
    • 100 Hz 0.1 amp + 300 Hz 0.033 amp + 500 0.02 amp + 700 0.0142
  • non-sine waves have a typical rich harmonics
  • making richer sound:
    • microtuning, changing wave shape, mixing oscillators in var. ratios


  • LPF, low pass filter (filtering out high frequencies)
  • resonance (filter emphasis):
    • adding amplitude to frequencies near the filter threshold
    • heavily used in electronic music
  • HPF
  • band pass filter (BP)
    • combination of LPF and HPF
  • band reject (the opposite of band BP); twich?
  • peak filter, emphasizing a band in the signal

Envelope (loudness contour)

  • time-related manipulation
  • Attack + Decay + Sustain; key is released => Release
  • Attack up to a few ms
  • Slow attack: bowed strings
  • Sustain
    • not time based, but level based (where decay ends)
    • from 0 to 1
    • if sustain is 1, decay has no effect
  • envelopes are used also for filters
    • it tells the main filter when to start being applied

LFO – low frequency oscillation

  • a nice feature is to sync its frequency with track tempo (1/8th)
  • tremollo guitar effect is using this

Frequency modulation, FM synthesis

  • a carrier (basic sound) and modulator signals
  • Yamaha DX7 (FM synthesis), 80’s
  • harmonic and inharmonic play important role in FM
  • a bit unpredictible compared to additive synth


  • polyphony-mono: retriggers envelope for each note
  • polyphony-legato: keeps the current envelope state
  • synthesizing drums:
    • short release
    • noise oscillator
    • LPF, resonance
February 5, 2022 |