Download Fast implementation for non-linear time-scaling of stereo signals In this paper we present an improved implementation of Duxbury’s adaptive phase-vocoder approach for audio time-stretching using non-linear time-scaling and temporal masked phase locking at transients [1]. We show that the previous algorithm has some limitations, notably its slow implementation and its incapacity to deal with stereo signals. We propose solutions to this problems including: an improved transient detection, a much faster implementation using the IFFT for re-synthesis and a method for stretching stereo signals without artifacts. Finally, we provide some graphical results and quantitative measures to illustrate our improvements.
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.