A MDCT based harmonic spectral bandwidth extension method

Modern audio coding technologies apply methods of bandwidth extension (BWE) to efficiently represent audio data at low bitrates. An established method is the well-known spectral band replication (SBR) that is part of MPEG High Efficiency Advanced Audio Coding (HE-AAC). However, if the signal features a distinct harmonic spectral structure, the use of these methods tends to result in audible artifacts, because the harmonic structure is not reconstructed correctly. In this paper a bandwidth extension method is proposed which eliminates the undesirable effects and allows for an efficient implementation in the Modified Discrete Cosine Transform (MDCT) domain. The proposed Harmonic Spectral Bandwidth Extension (HSBE) method uses arbitrary frequency shifts for modulating the replicated spectrum in a way that the harmonic structure of the signal is preserved. A listening test demonstrates the advantage of the proposed method compared to the state of the art.