A method, comprising: receiving audio data comprising N audio objects, the audio objects including audio signals and associated metadata, the metadata including at least audio object position data; and performing an audio object clustering process that produces M clusters from the N audio objects, M being a number less than N, wherein the clustering process comprises: selecting M representative audio objects; determining a cluster centroid position for each of the M clusters according to audio object position data of the audio object selected as representative of the cluster, each cluster centroid position being a single position that is representative of positions of all audio objects associated with a cluster; and determining gain contributions of the audio signal for each of the N audio objects to the M clusters by, for each of the N audio objects: minimizing a cost function with respect to the gain contributions of the audio object, the cost function including: - a first term representing a difference between a center of loudness position and an audio object position, wherein the center of loudness position is determined as a function of cluster centroid positions and the gain contributions to the M clusters of the audio object, and - a second term representing a distance between the audio object position and a cluster centroid position, such that the cost function penalizes gain contributions applied to a cluster centroid position that is relatively farther from the audio object position compared to a cluster centroid position that is relatively closer to the audio object position. receiving audio data comprising N audio objects, the audio objects including audio signals and associated metadata, the metadata including at least audio object position data; and performing an audio object clustering process that produces M clusters from the N audio objects, M being a number less than N, wherein the clustering process comprises: selecting M representative audio objects; determining a cluster centroid position for each of the M clusters according to audio object position data of the audio object selected as representative of the cluster, each cluster centroid position being a single position that is representative of positions of all audio objects associated with a cluster; and determining gain contributions of the audio signal for each of the N audio objects to the M clusters by, for each of the N audio objects: minimizing a cost function with respect to the gain contributions of the audio object, the cost function including: - a first term representing a difference between a center of loudness position and an audio object position, wherein the center of loudness position is determined as a function of cluster centroid positions and the gain contributions to the M clusters of the audio object, and - a second term representing a distance between the audio object position and a cluster centroid position, such that the cost function penalizes gain contributions applied to a cluster centroid position that is relatively farther from the audio object position compared to a cluster centroid position that is relatively closer to the audio object position. selecting M representative audio objects; determining a cluster centroid position for each of the M clusters according to audio object position data of the audio object selected as representative of the cluster, each cluster centroid position being a single position that is representative of positions of all audio objects associated with a cluster; and determining gain contributions of the audio signal for each of the N audio objects to the M clusters by, for each of the N audio objects: minimizing a cost function with respect to the gain contributions of the audio object, the cost function including: - a first term representing a difference between a center of loudness position and an audio object position, wherein the center of loudness position is determined as a function of cluster centroid positions and the gain contributions to the M clusters of the audio object, and - a second term representing a distance between the audio object position and a cluster centroid position, such that the cost function penalizes gain contributions applied to a cluster centroid position that is relatively farther from the audio object position compared to a cluster centroid position that is relatively closer to the audio object position. - a first term representing a difference between a center of loudness position and an audio object position, wherein the center of loudness position is determined as a function of cluster centroid positions and the gain contributions to the M clusters of the audio object, and - a second term representing a distance between the audio object position and a cluster centroid position, such that the cost function penalizes gain contributions applied to a cluster centroid position that is relatively farther from the audio object position compared to a cluster centroid position that is relatively closer to the audio object position.