Prasanga N. Samarasinghe

Interior and exterior sound field control using two dimensional higher-order variable-directivity sources

Spatial sound reproduction systems aim to produce a desired sound field over a volume of space. At high frequencies, the number of loudspeakers required is prohibitive. This paper shows that the use of loudspeakers with up to Nth order directivity allows reproduction over N times the bandwidth and produces a significantly attenuated exterior sound field. If the constraint on exterior cancellation of the field is removed, reproduction is possible over approximately 2N times the bandwidth. The use of higher order loudspeakers thus allows a significant reduction in the number of loudspeaker units, at the expense of increased complexity in each unit. For completeness, results are included for the generation of an exterior field with or without cancellation of the interior field.

Wavefield Analysis Over Large Areas Using Distributed Higher Order Microphones

Successful recording of large spatial soundfields is a prevailing challenge in acoustic signal processing due to the enormous numbers of microphones required. This paper presents the design and analysis of an array of higher order microphones that uses 2D wavefield translation to provide a mode matching solution to the height invariant recording problem. It is shown that the use of Mth order microphones significantly reduces the number of microphone units by a factor of 1/(2M + 1) at the expense of increased complexity at each microphone unit. Robustness of the proposed array is also analyzed based on the condition number of the translation matrix while discussing array configurations that result in low condition numbers. The white-noise gain (WNG) of the array is then derived to verify that improved WNG can be achieved when the translation matrix is well conditioned. Furthermore, the arrays performance is studied for interior soundfield recording as well as exterior soundfield recording using appropriate simulation examples.

Recent Advances in Active Noise Control Inside Automobile Cabins: Toward quieter cars

In this article, a compact tutorial of ANC techniques was presented with a review of their application in reducing undesired noise inside automobiles. Some of the recent advances have demonstrated significant improvements in the noise reduction levels as well as the cost and implementation complexity. While the aforementioned techniques discussed may individually focus on a particular noise field (e.g., road noise only, engine noise only), it is proven through research and commercial products that a combination of these strategies can deliver significant benefits in realistic conditions.

An efficient parameterization of the room transfer function

This paper proposes an efficient parameterization of the room transfer function (RTF). Typically, the RTF rapidly varies with varying source and receiver positions, hence requires an impractical number of point to point measurements to characterize a given room. Therefore, we derive a novel RTF parameterization that is robust to both receiver and source variations with the following salient features: 1) The parameterization is given in terms of a modal expansion of 3D basis functions. 2) The aforementioned modal expansion can be truncated at a finite number of modes given that the source and receiver locations are from two sizeable spatial regions, which are arbitrarily distributed. 3) The parameter weights/coefficients are independent of the source/receiver positions. Therefore, a finite set of coefficients is shown to be capable of accurately calculating the RTF between any two arbitrary points from a pre-defined spatial region where the source(s) lie and a pre-defined spatial region where the receiver(s) lie. A practical method to measure the RTF coefficients is also provided, which only requires a single microphone unit and a single loudspeaker unit, given that the room characteristics remain stationary over time. The accuracy of the above parameterization is verified using appropriate simulation examples.

Sparse complex FxLMS for active noise cancellation over spatial regions

In this paper, we investigate active noise control over large 2D spatial regions when the noise source is sparsely distributed. The ℓ1 relaxation technique originated from compressive sensing is adopted and based on that we develop the algorithm for two cases: multipoint noise cancellation and wave domain noise cancellation. This results in two new variants (i) zero-attracting multi-point complex FxLMS and (ii) zero-attracting wave domain complex FxLMS. Both approaches use a feedback control system, where a microphone array is distributed over the boundary of the control region to measure the residual noise signals and a loudspeaker array is placed outside the microphone array to generate the anti-noise signals. Simulation results demonstrate the performance and advantages of the proposed methods in terms of convergence rate and spatial noise reduction levels.

3D soundfield reproduction using higher order loudspeakers

Three dimensional surround sound reproduction over large areas is a prevailing challenge due to the enormous numbers of loudspeakers required. In this paper, we propose an array of higher order loudspeakers which provide a mode matching solution to the problem based on 3D wavefield translation. It is shown that for a given bandwidth, the use of Lth order sources significantly brings down the minimum loudspeaker requirement by a factor of 1=(L + 1)2. Furthermore, the array is shown to be capable of exterior field cancellation, increasing its performance in echoing environments. Design examples are given for interior field, exterior field and interior and exterior combined field reproduction.

On room impulse response between arbitrary points: An efficient parameterization

Spatial sound field recording and reproduction in reverberant rooms require the measurement of room transfer functions (RTF) followed by room equalization to correct undesired reflections. Typically, the RTF rapidly varies over the room and hence requires an infinite number of point to point measurements to characterize the room. This paper provides a modal based parameterization of the two dimensional acoustic transfer function over a sizeable spatial region in which the source(s) lie and a sizeable spatial region in which the receiver(s) are located. As a result, a finite set of modal coefficients is shown to be capable of predicting the RTF between any two arbitrary points from the aforementioned source and receiver regions.

In-car noise field analysis and multi-zone noise cancellation quality estimation

The loudspeaker array plays a key role in an active noise cancellation (ANC) system. In most in car ANC systems, the cars pre-installed multimedia loudspeakers are employed as the secondary sources of the ANC system. In this paper, we evaluate the in-car loudspeaker systems capability in multi-zone noise field cancellation by analyzing the simultaneous noise field at multiple control regions inside a car cabin. We show that the average noise power in multi-zone spatial configurations can be expressed using a series of coefficients, and that the noise field can be decomposed into several basis noise patterns. Based on this model, we also estimate the integrated loudspeaker systems maximum noise cancellation capability, which can be used to assist design optimization. Through analyzing the noise field measurements in a car, we show that the cars integrated stereo loudspeaker system can attenuate the in-car noise by approximately 20 dB for the head position of two seats simultaneously, and up to 200 Hz.

Spatial soundfield recording over a large area using distributed higher order microphones

Recording and reproduction of spatial sound fields over a large area is an unresolved problem in acoustic signal processing. This is due to the the inherent restriction in recording higher order harmonic components using practically realizable microphone arrays. As the frequency increases and as the region of interest becomes large the number of microphones needed in effective recording increases beyond practicality. In this paper, we show how to use higher order microphones, distributed in a large area, to record and accurately reconstruct 2D spatial sound fields. We use sound field coefficient translation between origins to combine distributed field recording to a single sound field over the entire region. We use simulation examples in (i) interior and (ii) exterior fields to corroborate our design.

Estimating the Direct-to-Reverberant Energy Ratio Using a Spherical Harmonics-Based Spatial Correlation Model

The direct-to-reverberant ratio (DRR), which describes the energy ratio between the direct and reverberant component of a soundfield, is an important parameter in many audio applications. In this paper, we present a multichannel algorithm, which utilizes the blind recordings of a spherical microphone array to estimate the DRR of interest. The algorithm is developed based on a spatial correlation model formulated in the spherical harmonics domain. This model expresses the cross correlation matrix of the recorded soundfield coefficients in terms of two spatial correlation matrices, one for direct sound and the other for reverberation. While the direct path arrives from the source, the reverberant path is considered to be a nondiffuse soundfield with varying directional gains. The direct and reverberant sound energies are estimated from the aforementioned spatial correlation model, which then leads to the DRR estimation. The practical feasibility of the proposed algorithm was evaluated using the speech corpus of the acoustic characterization of environments challenge. The experimental results revealed that the proposed method was able to effectively estimate the DRR of a large collection of reverberant speech recordings including various environmental noise types, room types and speakers.