Spectral Band Replication (SBR) is a state-of-the-art technology to enhance audio or speech codecs especially at low bitrates based on harmonic redundancy in the frequency domain. With SBR, it is possible to generate high frequency components of a full-band audio signal with a bitrate of a few kbps. In this paper, a bit reduction algorithm for SBR using the Masking Effect and threshold in quiet is proposed. The proposed algorithm reduces the SBR bitrate by modifying the envelope data of SBR in delta-coding scheme so that the modification cannot be perceived in the subjective sense. Experiments show that the proposed algorithm achieves about 10~12 % bit reduction for the envelope data of SBR based on the 3GPP Enhanced aacPlus codec at the bitrate of 24 kbps with no perceptive sound quality degradation
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