This study examined the influence of background noise on the localization of lead-lag noise-burst pairs and on echo threshold for the same stimuli. Experiments were conducted in an anechoic chamber with a leading stimulus delivered from a loudspeaker at 45 degrees to the right of center and a lagging stimulus from 45 degrees left. Lead and lag stimuli were 4-ms bursts of Gaussian noise. In experiment 1, with lead and lag at equal levels and the lag delay fixed at 2 ms, the perceived location of the image produced by the lead-lag stimulus was estimated from subjects' left/right judgments relative to bursts from a "comparitor" loudspeaker whose position could be adjusted. In experiment 2, the dominance of the leading burst on perceived location was measured by determining the increase in level of the lagging burst necessary to produce an image estimated to be centered at 0 degree azimuth. Experiment 3 was concerned with echo threshold. Subjects reported whether or not they heard a sound in the vicinity of the lagging loudspeaker as the lag-burst delay was varied. In all three experiments, data were obtained for four to five stimulus levels in quiet and for three levels of background white noise from a loudspeaker at 180 degrees. The results revealed a substantial weakening effect of background noise on the precedence effect in experiments 2 and 3, and a nonsignificant effect in experiment 1.

SUMMARYPacket loss and delay are the major network impairments for transporting real-time voice over IP networks. In the proposed system, multiple descriptions of the speech are used to take advantage of the packet path diversity. A new objective method is presented for predicting the perceived quality of multi-stream voice transmission. Also proposed is a multi-stream playout buffer algorithm, together with an adaptive parameter adjustment scheme, that maximizes the perceived speech quality via delay-loss trading. Experimental results showed that, compared to FECprotected single-path transmission, the proposed multi-stream transmission scheme achieves significant reductions in delay and packet loss rates as well as improved speech quality. key words: voice over IP, E-model, playout buffer

The current experiment examined the influence of noise on the precedence effect, focusing on the importance of noise source location. Listeners seated in an anechoic chamber judged whether the image produced by a lead-lag pair of 4-ms noise bursts (2-ms delay) was to the left or right of midline. The lag loudspeaker was fixed at 45° to the left or right, while the lead loudspeaker was positioned at a variable number of degrees to the opposite side. The angle of the lead loudspeaker producing 50% judgements favoring the lead was used to estimate its perceptual weighting relative to the lag. This weighting, which was quantified using the c metric developed by Shinn-Cunningham et al. [ 2923–2932 (1993)], strongly favored the lead when the sounds were presented in quiet. The value of c was reduced markedly when background broadband noise was introduced from 0° or 180° angles, supporting previous findings of a weakened precedence effect in noise. When the background noise source was off-midline, or lead-lag pairs of noise sources were used, the effects of noise on c were complex and asymmetric. [Work supported by NIH ♯DC01625.]

Objective This study investigated the feasibility of obtaining ear impressions for hearing aids by using 3-dimensional high-resolution computed tomography (HRCT) images. Study Design Case series. Setting One referral tertiary center. Subjects and Methods Hearing-impaired adults who were fitted with 1 or 2 behind-the-ear hearing aid(s) and had undergone temporal bone HRCT for various ear pathologies were enrolled in this study. Earmolds were fabricated from the impressions obtained using the conventional ear canal silicone injection technique and the HRCT reconstructed technique. Outer ear canal resonance frequencies and amplitude in open ears and those measured with silicon and HRCT reconstructed earmolds were determined through real-ear gain measurements, including real-ear unaided gain (REUG) and real-ear occluded gain (REOG), for comparison. Results A total of 50 HRCT reconstructed earmolds were compared with 50 conventional silicon injection earmolds. The average value of open ear canal resonance amplitude (REUG) for each ear was 0.41 to 16.76 dB. No statistically significant difference in resonance amplitude (REOG) was observed between silicon and reconstructed earmolds (paired t test, P > .05). The mean insertion loss (REOG-REUG) at all frequencies also did not differ significantly between the two earmolds (paired t test, P > .05). Conclusion According to our real-ear measurements, acoustic characteristics of the HRCT reconstructed earmolds were compatible with those of the silicone injection earmolds. Despite concerns about increased cost and radiation exposure, the HRCT reconstructed technique is a clinically useful and applicable method and can reduce potential safety complications for difficult cases.