Wavetable Synthesis

Wavetable Synthesis

• Idea: Save waveform, play it back when key is pressed

• Memory issues

  • Needs lots of memory (not a problem anymore)

  • Memory access is slow (needs lots of cache)

• Conceptual issues

  • Want note to last as long as key is held: looping is needed

  • May not have a wave for every key: pitch shifting is needed

  • Wave may have inappropriate envelope: envelope generation is desirable

  • May want to dynamicaly modify waveform: effects are desirable

Envelope: Attack, Decay, Sustain, Release

• ADSR model is standard envelope description

  • Attack: short ramp-up at start of note

  • Decay: short ramp-down just after attack

  • Sustain: constant hold level when decay is complete

  • Release: short ramp-down after key is released

• Often linear ramps, sometimes smoothed

• Used in pretty much every kind of synthesis

Sustain and Looping

• Want to maintain sustain level for as long as key is held down

• Infinite time stretching is a thing

• Techniques mentioned previously apply: usual is looping, i.e. time-domain stretching

• Loop start and end may be marked manually, or can try to infer

Soundfonts

• Standard file format for wavetables, set up for synthesizer consumption

• File format is immensely complicated, so use a library and think carefully about handling

• "General MIDI" synthesizers are almost always this: standard GM soundfonts are readily available