12. The data decompressor of claim 11 , wherein the decoder is configured to modify the indexed dictionary entry into a decoded musical note when the first indicator shows that modification is required.
11. A data decompressor for decompressing compressed data into melody data, wherein the compressed data comprises an index for designating an indexed dictionary entry in a dictionary, a first indicator for indicating whether modification of the indexed dictionary entry is required, a second indicator for indicating whether an update of the dictionary is required, a data part for modifying the indexed dictionary entry, the data decompressor comprising: a dictionary with a first plurality of dictionary entries; and a decoder configured to select the indexed dictionary entry from the dictionary according to the index in the compressed data, and further configured to output melody data based on the indexed dictionary entry.