Directivity of binaural noise reduction in spatial multiple noise-source arrangements for normal and impaired listeners

TLDR

The intelligibility level difference (ILD) quantifies the improvement in speech reception thresholds when target and interference signals are spatially separated. The study measured speech reception thresholds for up to three interfering sources at various azimuths in a virtual spatial setup using a rapid subjective assessment method. Normal listeners achieved maximal ILD at 105° or 255° azimuths, but ILD rapidly declined as more interferers or opposite‑side interferers were added, though continuous‑speech interferers attenuated this drop; the binaural system could suppress one azimuthal interference at a time and use pauses to suppress a second, whereas hearing‑impaired listeners showed reduced maximal ILD, diminished pause exploitation, and overall poorer binaural noise‑reduction performance.

Abstract

Speech reception thresholds (SRTs) were obtained for different azimuths of up to three interfering sound sources in a simulated ("virtual") spatial arrangement. For the SRT measurements a fast subjective threshold assessment method was used. The reduction in SRT relative to the reference threshold caused by spatial separation of target and interference signal is called the intelligibility level difference (ILD). For normal listeners, the maximum ILD was achieved at 105 degrees or 255 degrees azimuth of a single noise source when the target emanated from the front (0 degree azimuth). The ILD decreased rapidly if the number of interfering signals was increased and if they were located on opposite sides of the head. When using continuous speech as interference, this decrease of ILD was less pronounced. These findings indicate that the binaural system can suppress interference from only one azimuthal region at a time and can utilize temporal pauses in the interference to suppress a second interference from a different direction. For eight sensorineural impaired listeners, the maximum attainable ILD for one interfering noise source was reduced in a way not predictable from the audiogram. The ability to exploit pauses in the signal of an interfering talker was also reduced. Hence, hearing-impaired listeners are handicapped in realistic spatial interference situations both by an increased monaural SRT and a reduced binaural noise reduction ability.