Bidirectional propagation of sound

1. A method comprising:

receiving an input sound signal for a directional sound source having a source location and source orientation in a scene;

determining respective departure sound energies in different directions around the directional sound source based at least on directivity characteristics of the directional sound source and the source orientation;

identifying encoded directional reflection parameters that are associated with the source location of the directional sound source and a listener location;

based at least on the respective departure sound energies and the encoded directional reflection parameters, determining respective arrival sound energies arriving from different directions at the listener location; and

rendering directional sound reflections at the listener location by processing the input sound signal in accordance with the respective arrival sound energies.

2. The method of claim 1 , further comprising:

determining the respective departure sound energies by:

determining respective frequency band gains for the different directions by evaluating a source directivity function using the source orientation; and

converting the respective frequency band gains to energy values.

3. The method of claim 2 , wherein the source directivity function encodes frequency-dependent, spatially-varying directivity characteristics of the directional sound source for different frequency bands.

4. The method of claim 1 , wherein the rendering comprises:

inputting the input sound signal to multiple equalization filters to obtain multiple equalized sound signals, each equalized sound signal representing sound reflections arriving at the listener location from a corresponding arrival direction.

5. The method of claim 4 , further comprising:

configuring the multiple equalization filters in accordance with the respective arrival sound energies arriving at the listener location from the different directions.

6. The method of claim 5 , further comprising:

converting the respective arrival sound energies to frequency band-specific loudness settings; and

configuring the multiple equalization filters according to the frequency band-specific loudness settings.

7. The method of claim 6 , further comprising:

determining a listener orientation of a listener at the listener location and directional hearing characteristics of the listener; and

spatializing the multiple equalized sound signals to obtain binaural output at the listener that accounts for the listener orientation and the directional hearing characteristics.

8. The method of claim 7 , further comprising:

spatializing the multiple equalized sound signals using a head-related transfer function.

9. The method of claim 5 , further comprising:

periodically reconfiguring the multiple equalization filters at a visual frame rate based at least on changes to the source orientation.

10. A system comprising:

a processor; and

storage storing computer-readable instructions which, when executed by the processor, cause the system to:

receive an input sound signal for a directional sound source having a source location, source directivity characteristics, and a source orientation in a scene;

determine equalization filter settings based at least on the source orientation, the source directivity characteristics, and a listener location;

configure respective equalization filters with the equalization filter settings; and

render directional sound reflections at the listener location by passing the input sound signal through the respective equalization filters.

11. The system of claim 10 , wherein the computer-readable instructions, when executed by the processor, cause the system to:

determine respective arrival sound energies arriving at the listener location from different directions; and

configure the respective equalization filters based at least on the respective arrival sound energies, each equalization filter corresponding to a different arrival direction.

12. The system of claim 11 , wherein the computer-readable instructions, when executed by the processor, cause the system to:

identify encoded directional reflection parameters that are associated with the source location of the directional sound source and the listener location; and

determine the respective arrival sound energies using the encoded directional reflection parameters.

13. The system of claim 12 , wherein the computer-readable instructions, when executed by the processor, cause the system to:

determine respective departure sound direction energies in different directions around the directional sound source; and

compute the respective arrival sound energies using the encoded directional reflection parameters and the respective departure sound direction energies.

14. The system of claim 13 , wherein the directional sound reflections are rendered in a virtual scene and the encoded directional reflection parameters represent how sound travels from the source location to the listener location and is affected by different virtual structures within the virtual scene.

15. A system, comprising:

a processor; and

storage storing computer-readable instructions which, when executed by the processor, cause the system to:

receive an input sound signal for a directional sound source having a source location and a source orientation in a scene;

identify an encoded departure direction parameter corresponding to the source location of the directional sound source in the scene, the encoded departure direction parameter specifying a departure direction of initial sound on a sound path in which sound travels from the source location to a listener location around a structure in the scene; and

based at least on the encoded departure direction parameter and the input sound signal, render a directional sound at the listener location based at least on the source location and the source orientation of the directional sound source.

16. The system of claim 15 , wherein the computer-readable instructions, when executed by the processor, cause the system to:

identify the encoded departure direction parameter from a precomputed departure direction field based at least on the source location and the listener location,

the precomputed departure direction field specifying different departure directions of initial sound on different sound paths where sound travels from different source locations to different listener locations around different structures in the scene.

17. The system of claim 16 , wherein the computer-readable instructions, when executed by the processor, cause the system to:

compute the departure direction field from a virtual representation of the scene, the virtual representation identifying the different structures.

18. The system of claim 16 , wherein the computer-readable instructions, when executed by the processor, cause the system to:

obtain directivity characteristics of the directional sound source;

obtain directional hearing characteristics of a listener at the listener location and a listener orientation of the listener; and

render the initial sound as binaural output that accounts for the directional hearing characteristics of the listener, the listener orientation, the directivity characteristics of the directional sound source, and the source orientation of the directional sound source.

19. The system of claim 15 , wherein the structure is a virtual structure selected from a group comprising a virtual wall, virtual furniture, a virtual floor, a virtual ceiling, virtual vegetation, a virtual rock, a virtual hill, or a virtual building.

20. The system of claim 15 , wherein the structure comprises a wall that attenuates sound energy and the sound path travels from the source location, around the wall, and through a doorway to arrive at the listener location.

21. A method comprising:

receiving an input sound signal for a directional sound source having a source location, source directivity characteristics, and a source orientation in a scene;

determining equalization filter settings based at least on the source orientation, the source directivity characteristics, and a listener location;

configuring respective equalization filters with the equalization filter settings; and

rendering directional sound reflections at the listener location by passing the input sound signal through the respective equalization filters.

22. The method of claim 21 , further comprising:

determining respective arrival sound energies arriving at the listener location from different directions; and

configuring the respective equalization filters based at least on the respective arrival sound energies, each equalization filter corresponding to a different arrival direction.

23. The method of claim 22 , further comprising:

identifying encoded directional reflection parameters that are associated with the source location of the directional sound source and the listener location; and

determining the respective arrival sound energies using the encoded directional reflection parameters.

24. The method of claim 23 , further comprising:

determining respective departure sound direction energies in different directions around the directional sound source; and

computing the respective arrival sound energies using the encoded directional reflection parameters and the respective departure sound direction energies.

25. The method of claim 24 , wherein the directional sound reflections are rendered in a virtual scene and the encoded directional reflection parameters represent how sound travels from the source location to the listener location and is affected by different virtual structures within the virtual scene.