Abstract
Parametric multichannel audio coding represents an audio signal as one single audio channel plus side information. The side information contains estimates of perceptually relevant differences between the original audio channels. Usually, time difference, level difference, and coherence cues are considered. These cues determine, to a large degree, the auditory spatial image that is perceived when playing back multichannel audio signals. Level difference and time difference synthesis is simple: Different gain factors and delays are applied to the sum signal in subbands for generating the different decoder output channels. However, it is not as obvious how coherence cues can be synthesized. Several heuristic methods for coherence synthesis were proposed previously. In this paper, we are proposing a systematic approach for coherence synthesis. The coherence that is measured in the encoder between a pair of channels is reproduced in the decoder. For that purpose, de-correlation filters modeling late reverberation with impulse responses of a length of several hundred milliseconds are used, resulting in the ability of the scheme to generate naturally sounding diffuse sound. A method for reducing the computational complexity of the scheme is presented. The results of a subjective test indicate that the proposed scheme achieves good audio quality. Furthermore, the scheme was compared to a previous scheme without multichannel coherence synthesis and performs significantly better for all items tested.
Highlights
R ECENTLY, there has been a renewed interest in parametric stereo1 and multichannel audio coding techniques
The following definitions are used for ICTD, ICLD, and ICC for corresponding subband signals and of two audio channels with time index where and power of the signals are short-time estimates of the and, respectively
Width of Auditory Events and Envelopment: As implied by the results presented in Sections III-B and III-C, interaural coherence (IC) and ICC are related to the width of auditory events
Summary
R ECENTLY, there has been a renewed interest in parametric stereo and multichannel audio coding techniques. ) such that ICTD, ICLD, and ICC between the channels approximate those of the original audio signal. The described scheme is able to represent multichannel audio signals at a bitrate only slightly higher than what is required to represent a mono audio signal. ICTD, ICLD, and ICC between a channel pair contain one to two orders of magnitude less information than an audio waveform.
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