I am a musician myself (voc, perc), but I am not a synthesizer specialist. Howerver, AFAIK, in the early days of sound synthesis, all sounds were derived from simple waveforms (like sine, square, triange, chainsaw (like triangle but with a steep upward/downward flank), and so called envelopes (you could call them amplitude operators), which were "imposed" on those waveforms. This envelope was described by four parameters: attack, decay, sustain, and release (or short ASDR).

• A (time to reach maximum amplitude from keypress)
• D (time to drop to sustain amplitude after reaching max amplitude)
• S (amplitude to keep as long as the key is pressed)
• R (time to reach zero amplitude from S amplitude after key release)

AFAIK, A and S were linear, and the D and R parts of the envelope where parabolic.

  A       D       S      R
       o
      o o
     o   o
    o       o
   o           oooooooo
  o                   o
 o                     o
o                         o

Later 6 or more parameters where usual. Most of the modern soundcards still have ADSR/FM synthesizers build in. A famous specimen of these was the Yamaha OPL-3 chip all SoundBlaster cards had on them.

I hope this is somewhat interesting, ;)
so long,
Flexx