One of the difficulties in exploring musical timbre is combating the scriptist-inspired view of music. This view assumes that the script, in this case the musical score, contains all of the information about the music. A result of this perspective is the assumption that the smallest musical unit is the note, music's version of the atom. But just as physicists discovered that the atom was indeed divisible into smaller and smaller sections, musical notes can also be divided into smaller sections.
The best-known division of musical notes comes from the world of synthesizers, giving us the ADSR. This system breaks up the note into the Attack, the Decay, the Sustain, and the Release. The Attack is defined as the beginning of the note, up to the point that the amplitude has reached its maximum. The Decay marks the drop-off in amplitude after the Attack, followed by the Sustain's consistent volume level. Finally, the Release marks how quickly the volume drops to nothing after the Sustain portion. Simple synthesizers could control the timbre of a sound by specifying how long each of these sound portions lasted, with a linear increase or decrease of amplitude for the transient sections. These sections are determined solely by amplitude, with no consideration of frequency whatsoever. Fancier synthesizers do allow curves to the amplitude changes, for more subtle changes in timbre. Any of these synthesizers apply the ADSR amplitude envelope to a specified spectral pattern, either from an analog filter or a digital filter.
This system was never intended to analyze sounds, so its usefulness is limited. Acoustic instruments can increase in volume after the attack, or shift in spectral color without changing volume. In the next post I'll look at a different segmentation system that is better suited to analysis.