Coding and decoding of spherical coordinates using an optimized spherical quantization dictionary

A method implemented by a coding device and comprising:

• receiving a spatial direction parameter of a sound source in a sound scene;
• coding the received spatial direction parameter of a sound source, the spatial direction parameter being defined by spherical coordinates comprising an elevation coordinate and an azimuth coordinate, wherein a spherical quantization dictionary is defined on a 3D sphere by an elevation coding and an azimuth coding, and wherein:
• the elevation coding uses a scalar quantization, giving at least one coded elevation index (i) on a number of elevation levels (Nφ),
• the azimuth coding uses a scalar quantization, according to a number of points per level (Nθ(i)) depending on the coded elevation index (i),
• the number of points per level (Nθ(i)) is determined on the basis of two successive cumulative cardinality values (cumN(i), cumN(i−1)),
• the cumulative cardinality value (cumN(i)) for a coded elevation index (i) being representative of a number of points proportional to a total number of points and according to the area of a spherical zone comprising at least one zone delimited by an upper horizontal plane
• (
• ϕ
• =
• (
• i
• +
• 1
• 2
• )
• ⁢
• δ
• ϕ
• )
• of a positive elevation level of the coded elevation index (i) and a lower horizontal plane of the 3D sphere;
• and
• obtaining a quantized spatial direction index based on the elevation coding and the azimuth coding.