Parametric Array Processing

This chapter takes a different approach to signal enhancement using spherical microphone arrays: a physically-motivated parametric representation of the sound field is introduced. It is shown that the sound field can be manipulated to achieve noise reduct

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Parametric Array Processing

The general principle of parametric array processing is to employ an efficient parametric representation of the sound field including typically one or a few reference signals, and a small number of associated parameters. The advantage of such an approach is that the number of parameters is significantly lower than in classical array processing (see Chap. 7). A block diagram of a parametric array processing approach is shown in Fig. 8.1. Examples of parametric representations of the sound field include Directional Audio Coding (DirAC) [11], High Angular Resolution Planewave Expansion (HARPEX) [1] and computational auditory scene analysis (CASA) [4]. These representations can be used for spatial audio recording, coding and reproduction; source separation, noise reduction and dereverberation; and acoustic scene analysis and source localization. In this chapter, we will focus on parametric approaches to signal enhancement using the DirAC representation. The DirAC representation is based on two features that are relevant to the perception of spatial sound: the direction of arrival (DOA) and the diffuseness. Providing these features are accurately reproduced, this representation ensures that the interaural time differences (ITDs), interaural level differences (ILDs), and the interaural coherence are correctly perceived [16]. The advantage of integrating DirAC with a signal enhancement process is that any interference sources can be reproduced at their original position [9] relative to the desired source, in addition to being attenuated, thereby maintaining the naturalness of the listening experience but with increased speech quality and intelligibility. In this chapter, we first introduce a parametric model of the sound field. We then review the parameters that describe this sound field and how they can be estimated, and present filters that can be used to separate the two components of the sound field. Finally, we explore two applications of parametric array processing, namely, directional filtering and dereverberation. © Springer International Publishing Switzerland 2017 D. Jarrett et al., Theory and Applications of Spherical Microphone Array Processing, Springer Topics in Signal Processing 9, DOI 10.1007/978-3-319-42211-4_8

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8 Parametric Array Processing

Spherical Harmonic Transform

Mode Strength Compensation

Parameter Estimation (direction of arrival, signal-to-diffuse ratio, etc.)

Analysis

142

Parameters

Reference Signal

(Optional) Coding / Transmission / Storage Parameters

Single-Channel Filter or Time-Frequency Mask

Enhancement

Reference Signal

Processed Signal

Fig. 8.1 Block diagram of a parametric array processing approach. In the analysis stage, a reference signal is computed and a number of parameters are estimated. The reference signal and estimated parameters are transmitted or stored. In the enhancement stage, a single-channel filter or timefrequency mask is applied to the reference signal, optionally based on the estimated parameters, to yield a processed out