The proposed technology is concerned with a bit-efficient way to deliver phase information. This technology is to encode only inter-channel phase difference (IPD) parameter and to estimate overall phase difference (OPD) parameter at the decoder with transmitted inter-channel phase difference and channel level difference. The proposed technology reduces the bitrate for phase parameters compared to the case that both IPD parameters and OPD parameters are transmitted as specified in MPEG Parametric Stereo. The entropy coding scheme for phase parameters is improved utilizing the wrapping property of the phase parameters. We introduce phase smoothing at the decoder and adaptive control of quantization precision for phase parameters to minimize annoying artifact due to abrupt changes of quantized phase parameters. The proposed phase coding can improve stereo sound quality significantly and it was accepted as a part of MPEG-D USAC (Unified Speech and Audio Coding) standard.
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