An audio encoding system configured to generate a bitstream indicative of a downmix signal and spatial metadata for generating a multi-channel upmix signal from the downmix signal; the system comprising - a downmix processing unit configured to generate the downmix signal from a multi-channel input signal; wherein the downmix signal comprises m channels and wherein the multi-channel input signal comprises n channels; n, m being integers with m<n; - a parameter processing unit configured to determine spatial metadata for a frame of the multi-channel input signal, referred to as a spatial metadata frame, wherein a frame of the multi-channel input signal comprises a pre-determined number of samples of the multi-channel input signal, and wherein a spatial metadata frame comprises one or more sets (711, 712) of spatial parameters; and - a configuration unit configured to determine one or more control settings for the parameter processing unit based on one or more external settings; - wherein the one or more external settings comprise a target data-rate for the bitstream and wherein the one or more control settings comprise a maximum data-rate for the spatial metadata; - wherein the maximum data-rate for the spatial metadata is indicative of a maximum number of metadata bits for a spatial metadata frame; - wherein the one or more control settings comprise a temporal resolution setting indicative of a number of sets (711, 712) of spatial parameters per spatial metadata frame to be determined by the parameter processing unit; and wherein the parameter processing unit is configured to discard a set of spatial parameters from a current spatial metadata frame, if the current spatial metadata frame comprises a plurality of sets (711, 712) of spatial parameters and if it is determined that the number of bits of the current spatial metadata frame exceeds the maximum number of metadata bits, characterised in that - the one or more sets (711, 712) of spatial parameters are associated with corresponding one or more sampling points (583, 584); - the one or more sampling points (583, 584) are indicative of corresponding one or more time instants; - the parameter processing unit is configured to discard a first set of spatial parameters from the current spatial metadata frame, wherein the first set of spatial parameters is associated with a first sampling point prior to a second sampling point, if the plurality of sampling points (583, 584) of the current metadata frame is not associated with transients of the multi-channel input signal; and - the parameter processing unit is configured to discard the second set of spatial parameters from the current spatial metadata frame, if the plurality of sampling points (583, 584) of the current metadata frame is associated with transients of the multi-channel input signal. - a downmix processing unit configured to generate the downmix signal from a multi-channel input signal; wherein the downmix signal comprises m channels and wherein the multi-channel input signal comprises n channels; n, m being integers with m<n; - a parameter processing unit configured to determine spatial metadata for a frame of the multi-channel input signal, referred to as a spatial metadata frame, wherein a frame of the multi-channel input signal comprises a pre-determined number of samples of the multi-channel input signal, and wherein a spatial metadata frame comprises one or more sets (711, 712) of spatial parameters; and - a configuration unit configured to determine one or more control settings for the parameter processing unit based on one or more external settings; - wherein the one or more external settings comprise a target data-rate for the bitstream and wherein the one or more control settings comprise a maximum data-rate for the spatial metadata; - wherein the maximum data-rate for the spatial metadata is indicative of a maximum number of metadata bits for a spatial metadata frame; - wherein the one or more control settings comprise a temporal resolution setting indicative of a number of sets (711, 712) of spatial parameters per spatial metadata frame to be determined by the parameter processing unit; and wherein the parameter processing unit is configured to discard a set of spatial parameters from a current spatial metadata frame, if the current spatial metadata frame comprises a plurality of sets (711, 712) of spatial parameters and if it is determined that the number of bits of the current spatial metadata frame exceeds the maximum number of metadata bits, characterised in that - the one or more sets (711, 712) of spatial parameters are associated with corresponding one or more sampling points (583, 584); - the one or more sampling points (583, 584) are indicative of corresponding one or more time instants; - the parameter processing unit is configured to discard a first set of spatial parameters from the current spatial metadata frame, wherein the first set of spatial parameters is associated with a first sampling point prior to a second sampling point, if the plurality of sampling points (583, 584) of the current metadata frame is not associated with transients of the multi-channel input signal; and - the parameter processing unit is configured to discard the second set of spatial parameters from the current spatial metadata frame, if the plurality of sampling points (583, 584) of the current metadata frame is associated with transients of the multi-channel input signal.