Localization of amplitude-modulated high-frequency noise

Abstract

This study investigated whether listeners can use interaural time differences ͑ITDs͒ in the amplitude envelope to localize high-frequency sounds in a free field. Localization accuracy was measured for high-frequency ͑7 to 14 kHz͒ noise with and without an imposed amplitude modulation ͑AM͒ at 20, 80 or 320 Hz. Only AM at 320 Hz led to more accurate localization relative to the nonmodulated condition. The results of a control experiment suggest that the improvement in localization accuracy was due to an increase in stimulus bandwidth, rather than the temporal cues provided by the modulation.

Sound source localization of filtered noises by listeners with normal hearing: A statistical analysis

“…It is unlikely that microsecond envelope ITDs at the onsets and/or offsets of the noise bursts used in the present study could be used for sound source localization given that all stimuli were presented with 20-ms rise/fall times. Eberle et al (2000) have shown that it is highly unlikely that listeners use ongoing ITDs in the envelope of broadband stimuli (similar to ones used in the present study) in sound source localization in the free-field. These data and the use of 20-ms rise-fall times make it unlikely that the listeners in the present study used envelope-ITD cues as a basis for sound source localization.…”

Effects of amplitude modulation on sound localization in reverberant environments.

“…Therefore the benefit from modulation in reverberation in the side region may result from directional localization ability being impaired in the side region. Eberle et al (2000), which did not separate azimuth judgments by region, found modulation decreased angular error for very high modulation frequencies, but believe it was due to the sidebands increasing the bandwidth of the stimuli. In the present experiment, the modulation rate was not high enough for sidebands to increase the stimulus bandwidth.…”

“…Azimuth judgments were compared between conditions using a measure of angular error which has been used in past sound directional localization studies (Wightman & Kistler, 1989b;Eberle et al, 2000). Wightman and Kistler's (1989b) listeners were very accurate localizing sounds over headphones with a mean angular error of 19°, however their stimuli were generated using individualized HRTFs.…”

“…Wightman and Kistler's (1989b) listeners were very accurate localizing sounds over headphones with a mean angular error of 19°, however their stimuli were generated using individualized HRTFs. Eberle et al (2000) used a similar analysis using angular error of judgments collapsed across azimuth to measure directional localization and found a mean angular error of approximately 32° using the a direct estimate response method. A previous study that used a similar polar plot GUI response method measured a mean unsigned error of approximately 27° (Begault, Wenzel, and Anderson, 2001).…”

“…A complication with speech localization is that the tested speech signals are often low-pass filtered such that they do not contain frequencies in the range of 8-16 kHz, which have been shown to be critically important for localization of speech compared to broadband noise (Best, Carlile, Jin, and van Schaik, 2005). Eberle, McAnally, Martin, and Flanagan (2000) investigated localization ability using more reliable AM stimuli in an anechoic environment at modulation frequencies of 20, 80, and 320 Hz. They found localization was more accurate only when the signal was modulated at the highest frequency; however, they believe the effect was due to the broadening of the signal's spectral energy from side bands produced by modulation.…”