The audio-engine has a listener slot. The engine uses the object in this slot to determine the position, velocity, volume, and other attributes of the frame of reference for audio playback. These attributes are dynamic; every time update-audio runs, the listener attributes are queried and updated. The listener object must provide methods for the following generic words:

audio-position ( source/listener -- position )

audio-gain ( source/listener -- gain )

audio-velocity ( source/listener -- velocity )

audio-orientation ( listener -- orientation )

Some of these methods are shared with the Audio source protocol.

For simple applications, a tuple class is provided with a trivial implementation of these methods:

audio-listener