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

Filters

• 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

Miscellaneous

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