1. Interactive method of generating music employing a synthesizer; a programmable computer coupled to said synthesizer and capable of storing and running a program containing a music and sound control algorithm for generating music and sound control data in real time to be provided to said synthesizer and a performance algorithm for generating and interpreting performance control data; and at least one human-performer input device producing a signal in response to a physical music-performing gesture by a human performer; comprising the steps of: generating said music and sound control data in said computer to produce an ongoing, real-time, at least partially non-predeterminable musical composition; automatically supplying said music and sound control data from said computer to said synthesizer in accordance with said performance algorithm; scanning the signal from said human-performer input device at periodic intervals to determine whether said human performer is performing said gesture; if said signal indicates occurrence of said music-performance gesture, then altering said automatic performance algorithm in accordance with said signal and supplying said performance control data according to the altered performance algorithm; and producing audible music from said synthesizer, as determined by said performance, music, and sound control data, as audible feedback to said performer.