Download Representations of Audio Signals in Overcomplete Dictionaries: What is the Link Between Redundancy Factor and Coding Properties? This paper addresses the link between the size of the dictionary in overcomplete decompositions of signals and the rate-distortion properties when such decompositions are used for audio coding. We have performed several experiments with sets of nested dictionaries showing that very redundant shift-invariant and multi-scale dictionaries have a clear benefit at low bit-rates ; however for very low distortion a lot of atoms have to be encoded, in these cases orthogonal transforms such as the MDCT give better results.
Download Object Coding of Harmonic Sounds Using Sparse and Structured Representations Object coding allows audio compression at extremely low bit-rates, provided that the objects are correctly modelled and identified. In this study, a codec has been implemented on the basis of a sparse decomposition of the signal with a dictionary of InstrumentSpecific Harmonic atoms. The decomposition algorithm extracts “molecules” i.e. linear combinations of such atoms, considered as note-like objects. Thus, they can be coded efficiently using notespecific strategies. For signals containing only harmonic sounds, the obtained bitrates are very low, typically around 2 kbs, and informal listening tests against a standard sinusoidal coder show promising performances.