Quantization of spatial audio direction parameters

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:

• derive for each of the plurality of audio direction parameters, wherein each parameter comprises an elevation value and an azimuth value and wherein each parameter has an ordered position, a corresponding derived audio direction parameter comprising an elevation value and an azimuth value;
• rotate each derived audio direction parameter by the azimuth value of an audio direction parameter in the first position of the plurality of audio direction parameters;
• change the ordered position of an audio direction parameter to a further position coinciding with a position of a rotated derived audio direction parameter when the azimuth value of the audio direction parameter is closest to the azimuth value of the further rotated derived audio direction parameter compared to the azimuth values of other rotated derived audio direction parameters, followed by the apparatus being configured to determine for each of the plurality audio direction parameters a difference between each audio direction parameter and a corresponding rotated derived audio direction parameter;
• and
• quantize the difference for each of the plurality of audio direction parameters.

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:

• decode an index to provide a quantized azimuth value of an audio direction parameter in a first position of a plurality of ordered audio direction parameters, wherein each parameter comprises an elevation value and an azimuth value;
• derive for each of the plurality of audio direction parameters a corresponding derived audio direction parameter comprising an elevation value and an azimuth value;
• rotate each derived audio direction parameter by the azimuth value of the audio direction parameter in the first position of the plurality of audio direction parameters;
• decode an index to provide for each audio direction parameter a quantized difference between an audio direction parameter and their corresponding derived audio direction parameter;
• form, for each audio direction parameter, a quantized audio direction parameter by adding the quantized difference to their corresponding derived audio direction parameter;
• and
• decode an index representing an order for the plurality of quantized audio direction parameters and reordering the positions of the plurality of quantized audio direction parameters according to the order.

A method comprising:

• comprising:
• deriving for each of the plurality of audio direction parameters, wherein each parameter comprises an elevation value and an azimuth value and wherein each parameter has an ordered position, a corresponding derived audio direction parameter comprising an elevation value and an azimuth value;
• rotating each derived audio direction parameter by the azimuth value of an audio direction parameter in the first position of the plurality of audio direction parameters;
• changing the ordered position of an audio direction parameter to a further position coinciding with a position of a rotated derived audio direction parameter when the azimuth value of the audio direction parameter is closest to the azimuth value of the further rotated derived audio direction parameter compared to the azimuth values of other rotated derived audio direction parameters, followed by determining for each of the plurality audio direction parameters a difference between each audio direction parameter and a corresponding rotated derived audio direction parameter;
• and
• quantizing the difference for each of the plurality of audio direction parameters.