Using listening tests to demonstrate the subjective performance of a superdirective TV loudspeaker array

Abstract

Difficulties in understanding speech content in TV programmes are a common problem for listeners with age-related hearing loss. To address this problem, a superdirective TV loudspeaker array has been designed, which boosts the higher frequencies of the TV audio at selected positions in the room. The effectiveness of the system was assessed by objective measurements and subjective evaluation in the form of listening tests. The subjective performance of the array has been investigated in terms of the intelligibility of speech at the selected position, by applying a hearing loss simulator on normal hearing subjects, and the perceived quality for a normal hearing person outside of the selected position. For this purpose, two separate listening tests were performed, focusing on each of these two aspects. To evaluate the intelligibility of speech, short sentences were played back under different conditions to a panel of 33 subjects. Another 17 subjects participated in the evaluation of quality. At equal background noise level, it was found that for people listening via the hearing loss simulator, significantly more words were recognised using the array than without the array, showing that the intelligibility was improved. The speechto-noise-ratio, for which 50% of the words are recognised, was improved for these listeners from 0.5dB with the array switched off to-4.1dB with the array at 0dB gain for the array with respect to an ordinary TV speaker. The quality evaluation, based on ITU-R BS.1534 (MUSHRA), showed that at 0dB gain, the quality outside of the beam was still perceived as 'good' compared to the case where the array was switched off. However, increasing the gain to +3dB, reduced the quality which was then perceived on average as 'fair'.</p