8.2 Adsr

Adsr

Introduction

ADSR stands for attack, decay, sustain, and release and is used to model the timbre of an instrument. The timbre or tone quality is determined by various factors such as the way the sound is produced and the material of the instrument. Different families of instruments have their own characteristic ADSR profiles. The attack refers to the phase in which the sound is initiated. This could be the fast attack of a strum on a guitar or the slower one of a pipe organ. The decay phase occurs immediately after the attack impulse and describes how rapidly the sound dies. Some instruments like a drum have extremely fast decay and the sound is virtually nonexistent after the attack. The sustain profile of an instrument refers to how long the sound resonates for when it is played. String instruments such as a violin have an extremely long sustain because the violin’s sound box is receiving constant vibrational energy from the bowed string. Finally, the release phase describes how rapidly the sound fades away once the instrument is not being played.

Implementation

In order to synthesize different sounding instruments, the ADSR envelope could be applied directly to the output of the Karplus-Strong algorithm. Since the algorithm models string and certain percussion instruments, there were limitations on the diversity of instruments that could be synthesized using this technique. After modeling an instrument’s temporal characteristics with an ADSR envelope, one could apply it to the output of the Karplus-Strong by point-wise multiplication. By using ADSR, we were able to manipulate the guitar sounding output of the Karplus-Strong algorithm to sound like different instruments such as an organ or a bell.