Improved coding of tonal components in MPEG-4 AAC with SBR

Proposed is a new technique of effective regeneration of high-frequency tonal components in an augmented MPEG-4 AAC HE decoder. The basic idea is to synthesize the tonal components using the technique called synthetic sinusoidal coding that is already adopted in the MPEG-4 codecs in another context. Here, the idea is to mix this technique with standard Spectral Band Replication (SBR), i.e. to add some control information to a standard MPEG-4 AAC HE bitstream that is used to synthesize the high-frequency tonal components in a decoder. In that way, provided is proper synthesis of rapidly changing sinusoids as well as proper harmonic structure in the high-frequency band. The experiments show that the tool improves significantly the compression performance when added to an MPEG-4 AAC HE codec. This improvement has been confirmed by listening tests.