1. A method of compressing an audio signal, comprising: obtaining an audio signal that includes quantization indexes, identification of segments of said quantization indexes, and indexes of entropy codebooks that have been assigned to said segments, with a single entropy codebook index having been assigned to each said segment; identifying potential merging operations in which adjacent ones of the segments potentially would be merged with each other; estimating bit penalties for the potential merging operations; and performing at least one of the potential merging operations based on the estimated bit penalties, thereby obtaining a smaller updated set of segments of quantization indexes and corresponding assigned codebooks; and entropy encoding the quantization indexes in each of the segments in the smaller updated set by using the corresponding assigned entropy codebooks, thereby compressing the audio signal.