4. Modeling sound propagation

Once sound has been emitted by the sources, it travels through the environment until it reaches the listener's ears. During this journey, sound waves interact with the environment in a multitude of ways, in particular by reflecting and scattering off obstacles. Each reflection, or more generally indirect sound path, in turn reaches the listener's ears slightly attenuated and delayed in time. All these contributions add to the sound emitted by the source an effect characteristic of the environment in which it and the listener find themselves. Reproducing these environment-related effects is essential for good 3D localization of the sound source and coherent perception of the virtual environment.

Although it's no longer a question of simulating a sound source, but rather its transformation, the distinction between synthesis by sampling, by physical model or by analysis/synthesis...