Spatial audio parameter encoding and associated decoding

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

obtain direction parameter values associated with each of at least two time-frequency tile of a multichannel audio signal, the direction parameter values associated with each time-frequency tile comprises an elevation element and an azimuth element; and

compand encode each obtained direction parameter values, by the apparatus being caused to for each obtained parameter value:

quantize the elevation element;

determine a companding function based on the quantized elevation element and/or multichannel audio signal format;

generate a companded azimuth element based on the companding function applied to the azimuth element; and

quantize the companded azimuth element.

2 . The apparatus as claimed in claim 1 , wherein the apparatus is further caused to decompand the quantized companded azimuth element based on an inverse of the companding function.

3 . The apparatus as claimed in claim 2 , wherein the apparatus caused to compand encode each obtained direction parameter value is further caused to generate a codeword for each quantized elevation element and decompanded quantized companded azimuth element.

4 . The apparatus as claimed in claim 1 , wherein the apparatus caused to determine a companding function based on the quantized elevation element and/or multichannel audio signal format is caused to determine a companding function based on the quantized elevation element and the multichannel audio signal format.

5 . The apparatus as claimed in claim 4 , wherein the apparatus caused to compand encode each obtained direction parameter value is further caused to determine a quantization error for the compand encode and an average elevation encode, wherein the apparatus caused to determine an average elevation encode is configured to:

quantize an average elevation element for a sub-band within a frame; and

quantize the azimuth element based on a quantization grid with variable borders, and wherein the means is configured to select a compand encode output or an average elevation encode output based on the quantization error.

6 . The apparatus as claimed in claim 1 , wherein the apparatus caused to compand encode each obtained direction parameter value is further caused to generate a codeword for each quantized elevation element and quantized companded azimuth element.

7 . The apparatus as claimed in claim 1 , wherein the apparatus is further caused to determine a quantization grid based on an allocated number of bits for encoding each sub-band within a frame comprising sub-bands and time blocks based on a value of an energy ratio value associated with each obtained direction parameter value, wherein the apparatus caused to quantize the elevation element is caused to quantize the elevation element based on the quantization grid, and the apparatus caused to quantize the companded azimuth element is caused to quantize the companded azimuth based on the quantization grid.

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

obtain at least one encoded bitstream comprising: an encoded multichannel audio signal and compand encoded direction parameter values, the compand encoded direction parameter values are associated with at least two time-frequency tiles of the encoded multichannel audio signal, and each compand encoded direction parameter values comprises an encoded elevation element and a compand encoded azimuth element; and for each compand encoded direction parameter value:

decode the encoded elevation element;

determine a decompanding function based on the encoded elevation element and/or multichannel audio signal format; and

generate a decompanded azimuth element based on the decompanding function applied to the companded encoded azimuth element.

9 . The apparatus as claimed in claim 8 , wherein the apparatus caused to determine a decompanding function based on the encoded elevation element and/or multichannel audio signal format is further caused to determine a decompanding function based on the encoded elevation element and the multichannel audio signal format.

10 . The apparatus as claimed in claim 8 , wherein the apparatus caused to decode the encoded elevation element is further caused to decode a codeword for each encoded elevation element.

11 . The apparatus as claimed in claim 8 , wherein the apparatus is further caused to determine a quantization grid based on an allocated number of bits for encoding each sub-band within a frame comprising sub-bands and time blocks based on a value of an energy ratio value associated with the obtained direction parameter values, wherein the apparatus caused to decode a codeword for each encoded elevation element is caused to decode the encoded elevation element based on the quantization grid.

12 . A method comprising:

obtaining direction parameter values associated with each of at least two time-frequency tiles of a multichannel audio signal, the direction parameter values associated with each time-frequency tile comprises an elevation element and an azimuth element; and

compand encoding each obtained direction parameter values, wherein compand encoding each obtained direction parameter values comprises:

quantizing the elevation element;

determining a companding function based on the quantized elevation element and/or multichannel audio signal format;

generating a companded azimuth element based on the companding function applied to the azimuth element; and

quantizing the companded azimuth element.

13 . The method as claimed in claim 12 , further comprising decompanding the quantized companded azimuth element based on an inverse of the companding function.

14 . The method as claimed in claim 13 , wherein compand encoding each obtained direction parameter value further comprises generating a codeword for each quantized elevation element and decompanded quantized companded azimuth element.

15 . The method as claimed in claim 12 , wherein determining a companding function based on the quantized elevation element and/or multichannel audio signal format further comprises determining a companding function based on the quantized elevation element and the multichannel audio signal format.

16 . The method as claimed in claim 12 , wherein compand encoding each obtained direction parameter value further comprises generating a codeword for each quantized elevation element and quantized companded azimuth element.

17 . A method comprising:

obtaining at least one encoded bitstream comprising: an encoded multichannel audio signal and compand encoded direction parameter values, the compand encoded direction parameter values are associated with at least two time-frequency tiles of the encoded multichannel audio signal, and each compand encoded direction parameter value comprises an encoded elevation element and a companded encoded azimuth element; and for each compand encoded direction parameter value the method comprises:

decoding the encoded elevation element;

determining a decompanding function based on the encoded elevation element and/or encoded multichannel audio signal format; and

generating a decompanded azimuth element based on the decompanding function applied to the companded encoded azimuth element.

18 . The method as claimed in claim 17 , wherein the determining a decompanding function based on the encoded elevation element further and/or encoded multichannel audio signal format comprises determining a decompanding function based on the encoded elevation element and the encoded multichannel audio signal format.

19 . The method as claimed in claim 17 , wherein decoding the encoded elevation element further comprises decoding a codeword for each encoded elevation element.

20 . The method as claimed in claim 19 , further comprising determining a quantization grid based on an allocated number of bits for encoding each sub-band within a frame comprising sub-bands and time blocks based on a value of an energy ratio value associated with the obtained direction parameter values, wherein decoding a codeword for each encoded elevation element comprises decoding the encoded elevation element based on the quantization grid.