PURPOSE: A method of SFBBS(Scale Factor Based Bit Shifting) in FGS(Fine Granularity Scalability) audio coding is provided to overcome limitation of psycho-acoustic model by controlling an error in truncation of quantized data. CONSTITUTION: An audio signal in a spectral line is changed to quantized data of a plurality of sub-bands by the order from an MSB(Most Significant Bit) to an LSB(Least Significant Bit)(101). A plurality of scale factors corresponding to each of the sub-bands are determined according to noise tolerance of each sub-band(102). In case of excess of a critical vale, data quantized by each scale factor in the sub-band is subjected to bit shift(103). The quantized data is coded(104). The quantized data is truncated(106).
Scale factor based bit shifting in fine granularity scalability audio coding