Quantizing spatial audio 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:

• receive, from a multi-channel microphone system, metadata associated with a time frequency tile of one or more audio signals, wherein the metadata comprises at least two or more direct-to-total energy ratios associated with the time frequency tile;
• convert the two or more direct-to-total energy ratios to a diffuse-to-total energy ratio, wherein each respective one of the two or more direct-to-total energy ratios corresponds to a spatial audio direction and wherein each respective one of the two or more direct-to-total energy ratios indicates an amount of a total energy which is associated with its corresponding spatial audio direction;
• quantize the diffuse-to-total energy ratio using a first quantizer;
• determine a distribution factor of energy ratios dependent on a ratio of a first of the two or more direct-to-total energy ratios to the sum of the two or more direct-to-total energy ratios;
• select a further quantizer from a plurality of further quantizers using the quantized diffuse-to-total energy ratio;
• quantize the distribution factor of energy ratios using the selected further quantizer;
• and
• transmit or store an output comprised of an encoded audio transport signal and encoded metadata including the quantized distribution factor of energy ratios.