Can the diffuseness of sound sources in an auditory scene alter speech perception?

When amplification is used, sound sources are often presented over multiple loudspeakers, which can alter their timbre, and introduce comb-filtering effects. Increasing the diffuseness of a sound by presenting it over spatially separated loudspeakers might affect the listeners' ability to form a coherent auditory image of it, alter its perceived spatial position, and may even affect the extent to which it competes for the listener's attention. In addition, it can lead to comb-filtering effects that can alter the spectral profiles of sounds arriving at the ears. It is important to understand how these changes affect speech perception. In this study, young adults were asked to repeat nonsense sentences presented in either noise, babble, or speech. Participants were divided into two groups: (1) A Compact-Target Timbre group where the target sentences were presented over a single loudspeaker (compact target), while the masker was either presented over three loudspeakers (diffuse) or over a single loudspeaker (compact); (2) A Diffuse-Target Timbre group, where the target sentences were diffuse while the masker was either compact or diffuse. Timbre had no significant effect in the absence of a timbre contrast between target and masker. However, when there was a timbre contrast, the signal-to-noise ratios needed for 50% correct recognition of the target speech were higher (worse) when the masker was compact, and lower (better) when the target was compact. These results were consistent with the expected effects from comb filtering, and could also reflect a tendency for attention to be drawn towards compact sound sources.