Study on rounding errors of IntMDCT in perceptual audio coding

With the proliferation of broadband access and continuous decline of storage prize per gigabyte, there has been an increasing demand of audio solution that provides high sampling rate and high resolution. Lossless audio is undoubtedly the ultimate solution. In response to this demand, MPEG issued a call for proposal soliciting technology contributions that provides a state-of-art solution. At the technology end, lossless compression requires the usage of integer transform. The integer modified discrete cosine transform (IntMDCT) has been adopted in MPEG-4 scalable to lossless (SLS) coding to enable this efficient lossless operation. Because of rounding operations, rounding errors introduced by IntMDCT exist during the whole coding process. With the SLS having capability of using operations that spreads over the bitrate spectrum which ranges from lossy to lossless, it is of interest to study the effect of rounding errors in IntMDCT for operation of SLS in lossy mode. This paper analyzes the contributions of noise due to these errors. It is found that the noise introduced by rounding operations of IntMDCT does not affect the perceptual quality of the coded audio under any circumstances. As such, it concludes that the MDCT and IntMDCT filterbanks are interchangeable at lossy bitrate. With the fact that SLS uses both MDCT and IntMDCT, the finding in this paper suggests the possibility of using only IntMDCT filterbank.