Describing Musical Events

Many events, especially the higher level musical events are hierarchical in nature. For example in order to describe an event such as bowing a note on a string the event will be broken down into sub-events such as the following:

• Apply the bow to the string;
• Increase the velocity of the bow over some short time interval to create an attack, at the same time as controlling the downward force of the bow;
• Hold the velocity steady for some time interval;
• Decrease the velocity steadily for some time interval;
• Remove the bow from the instrument.

Such high-level events are referred to as compound events. All compound events no matter how complex eventually reduce down to low-level events, examples of which are given below:

• Evaluating expressions and assigning values to parameters;
• Changing the attributes of an instrument;
• Changing the attributes of a device;
• Applying a device to an instrument or removing it again;
• Coupling instruments together;
• Displaying text output in the shell window to give feedback about how a performance is progressing;
• Specifying output sources;
• Writing audio samples to output files.

The rest of this section takes a closer look at the various techniques which are commonly used to implement compound events.