159 The amplitude envelope Suppose that we wish to imitate a car driving towards us getting louder all the time and then driving past before stopping nearby and then driving away. The amplitude of the sound against time might well look like this: The first phase of the amplitude envelope, where the sound is getting louder is called the ‘attack phase’. The amplitude envelope is specified by giving six parameters. The first (AA) gives the change of amplitude at the end of each step during the attack phase and it must be a positive number. Usually the envelope starts with an amplitude of zero.
However it is possible to start with a non-zero amplitude if you have just interrupted a note on the same channel. The attack phase continues until the amplitude reaches the level given by the parameter ALA.