Selection of quantisation schemes for spatial audio parameter encoding

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:

• provide for each time frequency block of a sub band of an audio frame a spatial audio parameter comprising an azimuth and an elevation;
• determine a first distortion measure for the audio frame by determining a first distance measure for each time frequency block and summing the first distance measure for each time frequency block, wherein the first distance measure is an approximation of a distance between the elevation and azimuth and a quantized elevation a quantized azimuth according to a first quantisation scheme;
• determine a second distortion measure for the audio frame by determining a second distance measure for each time frequency block and summing the second distance measure for each time frequency block, wherein the second distance measure is an approximation of a distance between the elevation and azimuth and a quantized elevation and a quantized azimuth according to a second quantisation scheme;
• and
• select either the first quantization scheme or the second quantization scheme for quantising the elevation and the azimuth for all time frequency blocks of the sub band of the audio frame, wherein the selection is dependent on the first and second distortion measures.