In sound and music, an envelope describes how a sound changes over time. For example, a piano key, when struck and held, creates a near-immediate initial sound which gradually decreases in volume to zero. An envelope may relate to elements such as amplitude (volume), frequency or pitch.

The CZ series is a family of low-cost phase distortion synthesizers produced by Casio in the mid-1980s. Eight models of CZ synthesizers were released: the CZ-101, CZ-230S, CZ-1000, CZ-2000S, CZ-2600S, CZ-3000, CZ-5000, and the CZ-1. Additionally, the home-keyboard model CT-6500 used 48 phase distortion presets from the CZ line. The CZ synthesizers' price at the time of their introduction made programmable synthesizers affordable enough to be purchased by garage bands. Yamaha soon introduced their own low-cost digital synthesizers, including the DX-21 (1985) and Yamaha DX100, in light of the CZ series' success.