In general, techniques are described for grouping audio objects into clusters. In some examples, a device for audio signal processing comprises a cluster analysis module configured to group, based on spatial information for each of N audio objects, a plurality of audio objects that includes the N audio objects into L clusters, where L is less than N, wherein the cluster analysis module is configured to receive information from at least one of a transmission channel, a decoder, and a renderer, and wherein a maximum value for L is based on the information received. The device also comprises a downmix module configured to mix the plurality of audio objects into L audio streams, and a metadata downmix module configured to produce, based on the spatial information and the grouping, metadata that indicates spatial information for each of the L audio streams.