Estimation and quantization of ICC-dependent phase parameters for parametric stereo audio coding

Dong-Il Hyun,Young-Cheol Park,Dae Hee Youn

doi:10.1186/1687-4722-2012-27

Dong-Il Hyun, Young-Cheol Park + Show 1 more

Open Access

https://doi.org/10.1186/1687-4722-2012-27

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Abstract

Conventional parametric stereo (PS) audio coding employs inter-channel phase difference and overall phase difference as phase parameters. In this article, it is shown that those parameters cannot correctly represent the phase relationship between the stereo channels when inter-channel correlation (ICC) is less than one, which is common in practical situations. To solve this problem, we introduce new phase parameters, channel phase differences (CPDs), defined as the phase differences between the mono downmix and the stereo channels. Since CPDs have a descriptive relationship with ICC as well as inter-channel intensity difference, they are more relevant to represent the phase difference between the channels in practical situations. We also propose methods of synthesizing CPDs at the decoder. Through computer simulations and subjective listening tests, it is confirmed that the proposed methods produce significantly lower phase errors than conventional PS, and it can noticeably improve sound quality for stereo inputs with low ICCs.

Highlights

In an effort to efficiently represent multi-channel audio, spatial audio coding (SAC) has been studied extensively during the last decade [1,2,3,4]
It was shown that Overall phase difference (OPD) could be estimated using other spatial parameters, such as inter-channel intensity difference (IID), Inter-channel phase difference (IPD), and inter-channel correlation (ICC), at the decoder, which resulted in saving bits for OPD quantization
Based on the observations made for the phase difference sum (PDS) and IPD, we propose to use the CPD1 and CPD2 pair defined in Equation (9) for the description of the phase difference between the left and right inputs

Summary

Introduction

In an effort to efficiently represent multi-channel audio, spatial audio coding (SAC) has been studied extensively during the last decade [1,2,3,4]. It was shown that OPD could be estimated using other spatial parameters, such as inter-channel intensity difference (IID), IPD, and ICC, at the decoder, which resulted in saving bits for OPD quantization. A simple approach to the IPD distribution is to divide the total IPD in two and apply them to the left and right output channels, respectively This approach cannot guarantee the exact production of the original spatial impression, since the phase difference in this case cannot appropriately represent the spatial attribute of the sound source [6,11]. To solve this problem, the OPD parameter is commonly used for phase synthesis. By separating the OPD from the IPD, Equation (7) can be rewritten as

New phase parameters

Conclusions