Malcolm J. Hawksford

An oversampled digital PWM linearization technique for digital-to-analog conversion

An algorithmic-based linearization process for uniformly sampled digital pulsewidth modulation (PWM) is described. It is shown that linearization of the intrinsic distortion resulting in uniformly sampled PWM can be achieved by using a fractional delay digital filter embedded within a noise shaping re-quantizer. A technique termed direct PWM mapping is proposed as a pre-compensation filter scheme for applications in high-resolution digital-to-analog conversion.

A hybrid virtual bass system for optimized steady-state and transient performance

Bandwidth extension of a constrained loudspeaker system is regularly achieved employing nonlinear bass synthesis. The method operates on the doctrine of the missing fundamental whereby humans infer the presence of a fundamental tone when presented with a signal consisting of higher harmonics of said tone. Nonlinear devices and phase vocoders are commonly used for signal generation; both exhibiting deficiencies. A system is proposed where the two approaches are used in tandem via a mixing algorithm to suppress these deficiencies. Mixing is performed by signal transient content analysis in the frequency domain using constant-Q transforms. The hybrid approach is rated subjectively against various nonlinear device and phase vocoder techniques using the MUSHRA test method.

Individualized low-frequency response manipulation for multiple listeners using chameleon subwoofer arrays

Low-frequency acoustical responses are naturally position dependent across wide listening areas. This is predominantly due to room modes in small, closed spaces. Numerous methodologies have been proposed targeting room mode compensation to give an objectively even response across all listening locations. These techniques cannot guarantee, however, that every listener receives an equally pleasing subjective response. Chameleon subwoofer arrays (CSA) were originally developed to minimize low-frequency spatiotemporal variations by addressing frequency response errors at multiple listening locations using a subwoofer system consisting of multiple degrees of freedom. The CSA system can alternatively be utilized to control listening locations independently, allowing each listener to adjust their localized low-frequency response to their liking. This alternate CSA implementation is evaluated using a bespoke finite-difference time-domain (FDTD) algorithm for small home theater applications.