Abstract-Binaural

Binaural Cue Coding (BCC) is a method for multichannel spatial rendering based on one down-mixed audio channel and BCC side information. The BCC side information has a low data rate and it is derived from the multichannel encoder input signal. A natural application of BCC is multichannel audio data rate reduction since only a single down-mixed audio channel needs to be transmitted. An alternative BCC scheme for efficient joint transmission of independent source signals supports flexible spatial rendering at the decoder. This paper (Part I) discusses the most relevant binaural perception phenomena exploited by BCC. Based on that, it presents a psychoacoustically motivated approach for designing a BCC analyzer and synthesizer. This leads to a reference implementation for analysis and synthesis of stereophonic audio signals based on a Cochlear Filter Bank. BCC synthesizer implementations based on the FFT are presented as low-complexity alternatives. A subjective audio quality assessment of these implementations shows the robust performance of BCC for critical speech and audio material. Moreover, the results suggest that the performance given by the reference synthesizer is not significantly compromised when using a low-complexity FFT-based synthesizer. The companion paper (Part II) generalizes BCC analysis and synthesis for multichannel audio and proposes complete BCC schemes including quantization and coding. Part II also describes an alternative BCC scheme with flexible rendering capability at the decoder and proposes several applications for both BCC schemes. Index Terms-Audio coding, auditory filter bank, auditory scene synthesis, binaural source localization, coding of binaural spatial cues, spatial rendering. I. INTRODUCTION T HE data rate of traditional subband audio coders, such as AAC [1] and PAC [2], scales with the number of audio channels. If the channels are compressed independently, the data rate grows proportionally to the number of channels. Joint-channel coding techniques, such as "Sum-Difference Coding" [3], "Intensity Stereo Coding" (ISC) [4], and "Inter-Channel Prediction" [5] can reduce this growth rate. However, the resulting data rate for conventional stereophonic 1 material is still considerably higher than needed for representing the corresponding mono audio signal. Thus, the trade-off between audio bandwidth, coding artifacts, and number of channels Manuscript

Perceptual audio coders use an estimated masked threshold for the determination of the maximum permissible just-inaudible noise level introduced by quantization. This estimate is derived from a psychoacoustic model mimicking the properties of masking. Most psychoacoustic models for coding applications use a uniform (equal bandwidth) spectral decomposition as a first step to approximate the frequency selectivity of the human auditory system. However, the equal filter properties of the uniform subbands do not match the nonuniform characteristics of cochlear filters and reduce the precision of psychoacoustic modeling. Even so, uniform filter banks are applied because they are computationally efficient. This paper presents a psychoacoustic model based on an efficient nonuniform cochlear filter bank and a simple masked threshold estimation. The novel filter-bank structure employs cascaded low-order IIR filters and appropriate down-sampling to increase efficiency. The filter responses are optimized for the modeling of auditory masking effects. Results of the new psychoacoustic model applied to audio coding show better performance in terms of bit rate and/or quality of the new model in comparison with other state-of-the-art models using a uniform spectral decomposition. The low delay of the new model is particularly suitable for low-delay coders. Index Terms-Audio coding, filter bank, masked threshold, model of masking, perceptual model.

We introduce a new scheme for simultaneous placement of a number of sources in auditory space. The scheme is based on an assumption about the relevance of localization cues in different critical bands. Given the sum signal of a number of sources, i.e. a monophonic signal, and a set of parameters (side-information) the scheme is capable of generating a binaural signal by spatially placing the sources contained in the monophonic signal. Potential applications for the scheme are multi-talker desktop conferencing and audio coding. Preliminary experimental results suggest that the listener's ability to identify messages in a multi-talker environment significantly improves by enhancing a monophonic signal with the proposed scheme.

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