Bandwidth Extension of Audio
Spectral band replication (SBR) is a new technique that has gained popularity as an “add-on” to popular perceptual audio codecs such as MP-3 and the Advanced Audio Coding (AAC). New audio coders consisting of a marriage between SBR and the conventional audio coders have been formed, namely the MP3Pro and AAC+. In these algorithms, the lower spectrum is encoded using either MP-3 or AAC, whereas the high band is encoded using SBR. The key to the SBR algorithm is the information used to describe the high frequency portion of the signal. The primary design goal of this algorithm is to reconstruct the high band spectrum without introducing any aliasing artifacts and to provide good spectral and time resolution. A 64-band complex-valued polyphase filterbank is used at the analysis portion. At the encoder, the filterbank is used to obtain energy samples of the original input signal's high band. These energy samples are then used as reference values for the envelope adjustment scheme used at the decoder.
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