Physically correct distance-attenuation

[mbillingr]

The current distance-attenuation is just an ad-hoc 1 / d^2 formula with a cap for small distances.

Of course, attenuation depends on the medium the sound travels in and on the scene geometry (compare an open space vs. inside a narrow pipe). Some simplifications will be required.

Furthermore, it may be necessary to introduce a proper loudness model (power, sound pressure level, etc) in order to clarify what attenuation actually means.

TODO

• rehearse sound propagation physics
• define a simple/fast and physically correctish model
• Pull Request