 The sparse information available in the small bandwidth will probably be too limited to extract a proper envelope.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+.