Klaus Linhard

Noise‐reduction method for noise‐affected voice channels

A method that can be used not only for elimination of noise, for example in automatic speech recognition, but also to improve the voice quality for people, for instance during use of the speaker function of a car phone. The noise reduction is executed with two or multiple channels in such a manner that the temporal and architectural acoustical signal properties of speech and interference are utilized step-by-step and systematically. According to the method a pivotable, acoustic directional lobe is produced for the individual voice channels by respective digital directional filters and a linear phase estimation to correct for a phase difference between the two channels. The noise in the individual voice channels is estimated during speaking pauses, and the temporally stationary noise sources are damped by means of spectral subtraction. The individual voice channels are subsequently added whereby the statistical disturbances of spectral subtraction are averaged. Finally, the composite signal resulting from the addition is subsequently processed with a modified coherence function to damp diffuse noise and echo components.

3G-3 Optimum Array Configuration for Parametric Ultrasound Loudspeakers Using Standard Emitters

Ultrasound loudspeakers use parametric arrays to produce highly directional audible sound beams. For this purpose, high power ultrasound emitters with large apertures compared to ultrasound wavelengths are needed. They are commonly built from large film transducers or from small emitter capsules arranged to an array. Instead of using large film emitters, this work focuses on building ultrasound source arrays from cheap standard piezomorphs although common literature disadvises this approach. Therefore, a guideline is given how to nevertheless obtain good results. Since emitter distribution and arrangement within the source array have great influence on ultrasound beam characteristics, the generated audio beam is consequently affected significantly. This work examines different emitter and array configurations to determine optimum setups