Squelch is an effect in which the human auditory system is said to suppress room effects such as reverberation and coloration. Of particular interest is the squelch of room effects in everyday listening conditions: a listener listening to conversational speech in an ordinary room, with the talker and listener separated by a few meters. Traditionally, squelch has been considered a binaural effect- that is, attributable to the ears receiving somewhat different acoustical signals that lead to interaural timing and level differences. Few experiments have been done that attempt to further elucidate the mechanism or mechanisms underlying squelch. A major obstruction to studying squelch is that it is a subjective effect, and as such it is difficult to quantify in absolute terms.Three pilot experiments (PE1-PE3) were conducted to investigate squelch under everyday listening conditions. In these experiments, parameters thought to affect squelch were varied, sometimes in a multidimensional way, in a series of real room recordings. Listenersreported their perceptions of room effects after listening to the recordings over headphones, either via questionnaire (PE1) or rank-ordering (PE2,PE3). Parameters found to affect perceptions included distance between sound source ("talker") and recording microphones ("listener"), sound presentation level, presence of a spectral tilt, and binaurality. Interestingly, differences in experimental methodology apparently influenced listeners' experiences. Some listeners' responses were consistent with anti-squelch in PE1, but were consistent with binaural squelch in the other pilot experiments. Collectively, results of the pilot experiments suggested that squelch is not a purely binaural effect.It was hypothesized that the head related transfer function (HRTF) plays a role in squelch- specifcally, that a listener's own HRTF leads to the least amount of room effect being perceived, relative to "other" HRTFs. Two experiments were conducted to investigatethe effect of HRTF on listeners' perceptions of room effect. Both used the binaural synthesis technique to deliver psychoacoustically-accurate stimuli to listeners. The first experiment presented stimuli to listeners over headphones. Variations could be multidimensional. The experiment revealed significant effects of source distance and binaurality for all listeners. The second experiment utilized probe microphone recordings in the ear canals to present stimuli over loudspeakers. Results indicate a statistically signicant effect of at least some HRTFs on listeners' perceptions of room effect.
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