signals 104. The analysis processor 105 may be configured to generate the metadata which may comprise, for each time-frequency analysis interval, a direction parameter 108 and an energy ratio parameter 110 (and in some embodiments a coherence parameter, and a diffuseness parameter). The direction and energy ratio may in some embodiments be considered to be spatial audio parameters. In other words the spatial audio parameters comprise parameters which aim to characterize the sound-field created by the multi-channel signals (or two or more playback audio signals in general). 

In some embodiments the parameters generated may differ from frequency band to frequency band. Thus for example in band X all of the parameters are generated and transmitted, whereas in band Y only one of the parameters is generated and transmitted, and furthermore in band Z no parameters are generated or transmitted. A practical example of this may be that for some frequency bands such as the highest band some of the parameters are not required for perceptual reasons. The downmix signals 104 and the metadata 106 may be passed to an encoder 107. 

The encoder 107 may comprise an audio encoder core 109 which is configured to receive the downmix (or otherwise) signals 104 and generate a suitable encoding of these audio signals. The encoder 107 can in some embodiments be a computer (running suitable software stored on memory and on at least one processor), or alternatively a specific device utilizing, for example, FPGAs or ASICs. The encoding may be implemented using any suitable scheme. The encoder 107 may furthermore comprise a metadata encoder/quantizer 111 which is configured to receive the metadata and output an encoded or compressed form of the information. In some embodiments the encoder 107 may further interleave, multiplex to a single data stream or embed the metadata within encoded downmix signals before transmission or storage shown in Figure 1 by the dashed line. The multiplexing may be implemented using any suitable scheme. 

In the decoder side, the received or retrieved data (stream) may be received by a decoder/demultiplexer 133. The decoder/demultiplexer 133 may demultiplex the encoded streams and pass the audio encoded stream to a downmix extractor 

