Determination of spatial audio parameter encoding and associated decoding

1. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:

determine, for two or more audio signals, at least one spatial audio parameter for providing spatial audio reproduction, the at least one spatial audio parameter comprising an elevation and an azimuth component;

define a spherical grid generated by covering a sphere with smaller spheres by selecting a determined number of the smaller spheres for a first cross-section circle of the sphere, wherein the first cross-section circle is defined by a diameter of the sphere, determining a further number of cross-section circles of the sphere, and selecting for each of the further number of cross-section circles, the smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid; and

convert the elevation and azimuth component to an index value based on the defined spherical grid.

2. The apparatus as claimed in claim 1 , wherein the first cross-section circle defined by the diameter of the sphere is one of:

an equator of the sphere;

any circle having the same center as the sphere, and being situated on the sphere surface; and

a meridian of the sphere.

3. The apparatus as claimed in claim 1 , wherein the apparatus caused to define a spherical grid generated by covering a sphere with smaller spheres is further caused to define a circle index order associated with the first cross-section circle and the further number of cross-section circles.

4. The apparatus as claimed in claim 1 , wherein the spacing of the smaller spheres over the sphere is approximately equidistant with respect to the smaller spheres.

5. The apparatus as claimed in claim 1 , wherein the determined number of the smaller spheres for a first cross-section circle of the sphere and further numbers of the smaller spheres are determined based on an input quantization value.

6. The apparatus as claimed in claim 1 , wherein the apparatus caused to convert the elevation and azimuth component to the index value based on the defined spherical grid is further caused to:

determine a cross-section circle index value based on a defined order of the elevation component;

determine an intra-circle index value based on the azimuth component; and

generate the index value based on combining the intra-circle index value and an offset value based on the cross-section circle index value.

7. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least on processor, cause the apparatus at least to:

determine, at least one direction index associated with two or more audio signals for providing spatial audio reproduction, the at least one direction index representing a spatial parameter with an elevation and an azimuth component;

determine a spherical grid generated by covering a sphere with smaller spheres by selecting a determined number of the smaller spheres for a first cross-section circle of the sphere, wherein the first cross-section circle is defined by a diameter of the sphere, determining a further number of cross-section circles of the sphere, and selecting for each of the further number of cross-section circles, the smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid;

convert the at least one direction index to a quantized elevation and a quantized azimuth representation of the elevation and the azimuth component; and

convert the quantized elevation and the quantized azimuth representation of the elevation and the azimuth component to an index value based on the determined spherical grid.

8. The apparatus as claimed in claim 7 , wherein the first cross-section circle defined by the diameter of the sphere is one of:

an equator of the sphere;

any circle having the same center as the sphere, and being situated on the sphere surface; and

a meridian of the sphere.

9. The apparatus as claimed in claim 7 , wherein the apparatus caused to define a spherical grid generated by covering a sphere with smaller spheres is further caused to define a circle index order associated with the first cross-section circle and the further number of cross-section circles.

10. The apparatus as claimed in claim 7 , wherein the spacing of the smaller spheres over the sphere is approximately equidistant with respect to the smaller spheres.

11. The apparatus as claimed in claim 7 , wherein the determined number of the smaller spheres for a first cross-section circle of the sphere and further numbers of the smaller spheres as determined based on an input quantization value.

12. The apparatus as claimed in claim 7 , wherein the apparatus caused to convert the quantized elevation and the quantized azimuth representation of the elevation and the azimuth component to the index value based on the determined spherical grid is further caused to:

determine a cross-section circle index value based on the index value;

determine the quantized elevation representation of the elevation component based on the cross-section circle index value; and

generate the quantized azimuth representation of the azimuth component based on a reminder index value after removing an offset associated with the cross-section circle index value from the index value.

13. A method comprising:

determining, for two or more audio signals, at least one spatial audio parameter for providing spatial audio reproduction, the at least one spatial audio parameter comprising an elevation and an azimuth component;

defining a spherical grid generated by covering a sphere with smaller spheres by selecting a determined number of the smaller spheres for a first cross-section circle of the sphere, wherein the first cross-section circle is defined by a diameter of the sphere, determining a further number of cross-section circles of the sphere, and selecting for each of the further number of cross-section circles, the smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid; and

converting the elevation and azimuth component to an index value based on the defined spherical grid.

14. The apparatus as claimed in claim 13 , wherein the first cross-section circle defined by the diameter of the sphere is one of:

an equator of the sphere;

any circle having the same center as the sphere, and being situated on the sphere surface; and

a meridian of the sphere.

15. A method comprising:

determining the at least one direction index associated with two or more audio signals for providing spatial audio reproduction, the at least one direction index representing a spatial parameter comprising an elevation and an azimuth component;

determining a spherical grid generated by covering a sphere with smaller spheres by selecting a determined number of the smaller spheres for a first cross-section circle of the sphere, wherein the first cross-section circle is defined by a diameter of the sphere, determining a further number of cross-section circles of the sphere, and selecting for each of the further number of cross-section circles, the smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid;

converting the at least one direction index to a quantized elevation and a quantized azimuth representation of the elevation and the azimuth component; and

converting the quantized elevation and the quantized azimuth representation of the elevation and the azimuth component to an index value based on the determined spherical grid.

16. The apparatus as claimed in claim 15 , wherein the first cross-section circle defined by the diameter of the sphere is one of:

an equator of the sphere;

any circle having the same center as the sphere, and being situated on the sphere surface; and

a meridian of the sphere.

17. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:

determine, for two or more audio signals, at least one spatial audio parameter for providing spatial audio reproduction, the at least one spatial audio parameter comprising an elevation and an azimuth component;

define a spherical grid generated by covering a sphere with smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid; and

convert the elevation and azimuth component to an index value based on the defined spherical grid by:

determining a cross-section circle index value based on a defined order of the elevation component;

determining an intra-circle index value based on the azimuth component; and

generating the index value based on combining the intra-circle index value and an offset value based on the cross-section circle index value.

18. A method comprising:

determining, for two or more audio signals, at least one spatial audio parameter for providing spatial audio reproduction, the at least one spatial audio parameter comprising an elevation and an azimuth component;

defining a spherical grid generated by covering a sphere with smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid; and

converting the elevation and azimuth component to an index value based on the defined spherical grid by:

determining a cross-section circle index value based on a defined order of the elevation component;

determining an intra-circle index value based on the azimuth component; and

generating the index value based on combining the intra-circle index value and an offset value based on the cross-section circle index value.

19. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least on processor, cause the apparatus at least to:

determine, at least one direction index associated with two or more audio signals for providing spatial audio reproduction, the at least one direction index representing a spatial parameter with an elevation and an azimuth component;

determine a spherical grid generated by covering a sphere with smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid;

convert the at least one direction index to a quantized elevation and a quantized azimuth representation of the elevation and the azimuth component; and

convert the quantized elevation and the quantized azimuth representation of the elevation and the azimuth component to an index value based on the determined spherical grid by:

determining a cross-section circle index value based on the index value;

determining the quantized elevation representation of the elevation component based on the cross-section circle index value; and

generating the quantized azimuth representation of the azimuth component based on a reminder index value after removing an offset associated with the cross-section circle index value from the index value.

20. A method comprising:

determining, at least one direction index associated with two or more audio signals for providing spatial audio reproduction, the at least one direction index representing a spatial parameter with an elevation and an azimuth component;

determining a spherical grid generated by covering a sphere with smaller spheres, wherein the smaller spheres are each smaller than the sphere, and wherein the centers of the smaller spheres define points of the spherical grid;

converting the at least one direction index to a quantized elevation and a quantized azimuth representation of the elevation and the azimuth component; and

converting the quantized elevation and the quantized azimuth representation of the elevation and the azimuth component to an index value based on the determined spherical grid by:

determining a cross-section circle index value based on the index value;

determining the quantized elevation representation of the elevation component based on the cross-section circle index value; and

generating the quantized azimuth representation of the azimuth component based on a reminder index value after removing an offset associated with the cross-section circle index value from the index value.