Time Domain Optimization of Filters Used in a Loudspeaker Array for Personal Audio

Abstract

This paper describes a time domain design method for calculating the coefficients of FIR filters used to drive a loudspeaker array for personal audio. A motivating application is to boost the television audio in a certain spatial region with the aim of increasing the speech intelligibility of the hearing impaired. As the array is of small size, superdirective beamforming is applied to increase the low and mid frequency directional performance of the radiator. The filters for such arrays have previously been designed one frequency at a time, leading to non-causal filters that require a modeling delay for real time implementation. By posing the filter optimization in the time domain, the filter responses can be causally constrained, and the optimization is performed once for all frequencies. This paper considers the performance of such filters by carrying out off-line simulations, firstly using the impulse responses of point sources in the free field, and then with the measured responses of a loudspeaker array in an anechoic chamber. The simulation results show how the time domain optimization allows the creation of filters with either a low order or a low modeling delay.Index Terms-Array signal processing, personal audio, time domain optimization.

A Unified Approach to Generating Sound Zones Using Variable Span Linear Filters

“…Also note that when x[n] is a J-periodic signal with N = J ≥ K and γ is optimized per frequency bin rather than globally as in (9), it decouples into J independent generalized eigenvalue problems, whose solutions are identical to the solution of ACC in the frequency domain of J frequency bins. For more on the ACC time domain approaches see [20,21,23,28].…”

“…Therefore, many methods have tried to modify either ACC or PM to get an intermediate solution which allows us to trade-off distortion for contrast. Examples of such methods can be found in [18][19][20][21][22][23].…”

Sound Zones As An Optimal Filtering Problem

“…Note that the approximation is exact if rank(Rs) = V . From (13), we see that the speech distortion objective only depends on the first V elements, denoted as aV , of the vector a. As seen from (12), the remaining M − V elements only increase the noise suppression objective and should, therefore, be set to zero.…”

“…However, this improvement in the reconstruction quality of the desired sound field came at the expense of a much higher zone leakage, i.e., a smaller acoustic contrast between the bright and dark zone. Therefore, a number of methods [11][12][13][14][15][16] have sought to modify and/or combine ACC and PM so that a better trade-off between signal distortion and zone leakage is obtained.…”

Surround by Sound: A Review of Spatial Audio Recording and Reproduction

“…More recent works have been focusing on the combination of the ACC and PM formulations using the Lagrangian with a weighting factor to tune the trade-off between the two performance measures, i.e., the acoustic contrast and bright zone error (i.e., the reproduction error within the bright zone) [147][148][149]. The idea of performing time-domain filters for personal audio was recently investigated [150].…”