Spherical Harmonic Decomposition of a Sound Field Based on Microphones Around the Circumference of a Human Head

We present a method for decomposing a sound field into spherical harmonics (SH) based on observations of the sound field around the circumference of a human head. The method is based on the analytical solution for observations of the sound field along the equator of a rigid sphere that we presented recently. The present method incorporates a calibration stage in which the microphone signals for sound sources at a suitable set of calibration positions are projected onto the SH decomposition of the same sound field on the surface of a notional rigid sphere by means of a linear filtering operation. The filter coefficients are computed from the calibration data via a least-squares fit. We present an evaluation of the method based on binaural rendering of numerically simulated signals for an array of 18 microphones providing 8th SH order to demonstrate its effectiveness

A Head-Mounted Microphone Array for Binaural Rendering

We recently presented a method for obtaining a spherical harmonic representation of a sound field based on microphones along the equator of a rigid spherical object that ideally has a size similar to that of a human head. We refer to this setup as an equatorial microphone array. Even more recently, we presented an extension of this method that allows for employing a scattering object that is approximately spherical such as a human head. The present paper provides an overview as well as a juxtaposition of the two solutions. We present an instrumental evaluation based on the application of binaural rendering of the captured sound fields by analysing simulated binaural transfer functions of both methods for a variety of scenarios

The Far-Field Equatorial Array for Binaural Rendering

We present a method for obtaining a spherical harmonic representation of a sound field based on a microphone array along the equator of a rigid spherical scatterer. The two-dimensional plane wave de-composition of the incoming sound field is computed from the microphone signals. The influence of the scatterer is removed under the assumption of distant sound sources, and the result is converted to a spherical harmonic (SH) representation, which in turn can be rendered binaurally. The approach requires an order of magnitude fewer microphones compared to conventional spherical arrays that operate at the same SH order at the expense of not being able to accurately represent non-horizontally-propagating sound fields. Although the scattering removal is not perfect at high frequencies at low harmonic orders, numerical evaluation demonstrates the effectiveness of the approach

Towards the prediction of perceived room acoustical similarity

Understanding perceived room acoustical similarity is crucial to generating perceptually optimized audio rendering algorithms that maximize the perceived quality while minimizing the computational cost. In this paper we present a perceptual study in which listeners compare dynamic binaural renderings generated from spatial room impulse responses (SRIRs) obtained in several rooms and positions and are asked to identify whether they belong to the same space. The perceptual results, together with monaural room acoustical parameters, are used to generate a prediction model that estimates the perceived similarity of two SRIRs

Spherical harmonic decomposition of a sound field based on observations along the equator of a rigid spherical scatterer

We present a method for computing a spherical harmonic representation of a sound field based on observations of the sound pressure along the equator of a rigid spherical scatterer. Our proposed solution assumes that the captured sound field is height invariant so that it can be represented by a two-dimensional (2D) plane wave decomposition (PWD). The 2D PWD is embedded in a three-dimensional representation of the sound field, which allows for perfectly undoing the effect of the spherical scattering object. If the assumption of height invariance is fulfilled, then the proposed solution is at least as accurate as a conventional spherical microphone array of the same spherical harmonic order, which requires a multiple of the number of sensors. Our targeted application is binaural rendering of the captured sound field. We demonstrate by analyzing the binaural output signals that violations of the assumptions that the solution is based on—particularly height invariance and consequently also horizontal propagation—lead to errors of moderate magnitude