Hybrid predictive and parametric stereo coding for voice and audio communications

The transmission of stereo audio in voice calls helps to improve immersion and user experience. However stereo coding has primarily been studied for broadcast or streaming applications. To extend the capabilities of 3GPP EVS, a hybrid stereo coding scheme combining predictive and parametric coding is proposed to meet the requirements of real-time communications. After the stereo channels are time-aligned, a sum-difference (M/S) decomposition is performed. The prediction of the side signal by the mid signal is used to capture the other spatial cues. The prediction residue can be parametrically modeled by a stereo filling or, at higher bitrates and for low frequencies, discretely coded. Listening test results confirm the stereo coding scheme’s great flexibility and robustness under different recording conditions, as well as the minimal quality impact of the low-bitrate and low-delay constraints.