Character-based games or interactive drama have been modelled as a network of inter-connected pre-recorded scenes in a "story-net" arrangement of branching nodes. At each node in the network, a decision is required as to which of three of four possible scenes will be played out next with there being a common direction of travel through the scripted narrative such that the user will eventually reach the, or one of a number of possible, final scenes. Examples of different narrative structures, from the non-interactive "linear" form through the introduction of various effects and game-playing elements to full branching story structures, are described in "Flawed Methods for Interactive Storytelling" by Chris Crawford, Interactive Entertainment Design, Vol 7, No 4, April 1994. The problems of the vast amount of data required to provide even a few alternative paths through a story structure as opposed to the constraints of traditional (linear) narrative techniques are discussed and, whilst a solution is claimed, the details are withheld. These problems of interactivity against storyline are further discussed in an article by the same author "Interactivity, Plot, Free Will, Determinism, Quantum Mechanics and Temporal Irreversibility" Interactive Entertainment Design, Vol 8, No 4, April 1995.
Considering just the audio side of interactive entertainment, the character based games or interactive drama require dialogue between the characters: speech is the easiest way to convey meaning and feeling and thus generate a feeling of immersion for the user by relating to the characters. In traditional systems, such as those described by Crawford, this has been done using long pre-recorded sequences of speech providing the soundtrack to the selected scene following each branch point of the story. Even as a purely audio entertainment, such systems are still tied to the ongoing branch structure which, in addition to having long periods passing without variation, is still prohibitive in the amount of data required to be stored for even relatively few branches.