An audio data format in which an instrument is described using a combination of sound samples and articulation instructions which determine modifications made to the sound sample is provided. The instruments form a first, initial layer, with a second layer having presets which can be user-defined to provide additional articulation instructions which can modify the articulation instructions at the instrument level. The articulation instructions are specified using various parameters (78). The present invention provides a format in which all of the parameters (78) are specified in units which relate to a physical phenomena, and thus are not tied to any particular machine for creating or playing the audio samples. The articulation parameters include generators (86) and modulators (88), which provide a connection between a real-time signal and a generator. The parameter units are specified in perceptually additive units, to make the data portable and easily edited. New units are defined to give perceptual additive parameters throughout.