A method comprising: determining a first coding bitrate for at least one first frame audio signal multi-channel parameter and a second coding bitrate for at least one second frame audio signal multi-channel parameter, wherein the combined first and second coding bitrate is less than a bitrate limit; determining for a first frame the at least one first frame audio signal multi-channel parameter; generating an encoded first frame audio signal multi-channel parameter within the first coding bitrate from the at least one first frame audio signal multi-channel parameter; determining for a second frame the at least one second frame audio signal multi-channel parameter; generating an encoded at least one second frame audio signal multi-channel parameter within the second coding bitrate from the at least one second frame audio signal multi-channel parameter; and multiplexing the encoded at least one first frame audio signal multi-channel parameter and the encoded at least one second frame audio signal multi-channel parameter, characterized in that wherein generating an encoded first frame audio signal multi-channel parameter within the first coding bitrate from the at least one first frame audio signal multi-channel parameter or generating an encoded second frame audio signal multi-channel parameter within the second coding bitrate from the at least one second frame audio signal multi-channel parameter comprises: generating codebook indices for groups of the at least one first frame audio signal multi-channel parameter or the at least one second frame audio signal multi-channel parameter respectively using separate vector quantization codebooks; generating a combined vector quantization codebook from the separate quantization codebooks; and generating a combined vector quantization index for the combined vector quantization codebook from the codebook indices for groups, wherein the number of bits used to identify the combined vector quantization index is fewer than a combined number of bits used by the codebook indices for the separate groups. determining a first coding bitrate for at least one first frame audio signal multi-channel parameter and a second coding bitrate for at least one second frame audio signal multi-channel parameter, wherein the combined first and second coding bitrate is less than a bitrate limit; determining for a first frame the at least one first frame audio signal multi-channel parameter; generating an encoded first frame audio signal multi-channel parameter within the first coding bitrate from the at least one first frame audio signal multi-channel parameter; determining for a second frame the at least one second frame audio signal multi-channel parameter; generating an encoded at least one second frame audio signal multi-channel parameter within the second coding bitrate from the at least one second frame audio signal multi-channel parameter; and multiplexing the encoded at least one first frame audio signal multi-channel parameter and the encoded at least one second frame audio signal multi-channel parameter, characterized in that wherein generating an encoded first frame audio signal multi-channel parameter within the first coding bitrate from the at least one first frame audio signal multi-channel parameter or generating an encoded second frame audio signal multi-channel parameter within the second coding bitrate from the at least one second frame audio signal multi-channel parameter comprises: generating codebook indices for groups of the at least one first frame audio signal multi-channel parameter or the at least one second frame audio signal multi-channel parameter respectively using separate vector quantization codebooks; generating a combined vector quantization codebook from the separate quantization codebooks; and generating a combined vector quantization index for the combined vector quantization codebook from the codebook indices for groups, wherein the number of bits used to identify the combined vector quantization index is fewer than a combined number of bits used by the codebook indices for the separate groups.