Anna K. Nábělek

Monaural and binaural speech perception in reverberation for listeners of various ages

The Modified Rhyme Test (MRT) was processed through a room (volume 165 m3, reverberation time T = 0.4, 0.8, and 1.2 s). For both binaural and monaural earphone listening the tests were recorded with a manikin (Kemar) and equalization filters to compensate for the ear canal effect. Six groups of subjects, ten subjects each, had mean ages of 10, 27, 42, 54, 64 and 72 years and average hearing threshold levels. HTLs (for 0.5, 1, and 2 kHz) of 2.7, 5.6, 6.0, 10.9, 14.4, 17.5 dB, respectively. The individual scores for the MRT without reverberation were between 90% and 100% at 70 dB SPL. Children and the elderly required from 10 to 20 dB higher SPLs than young adults to obtain maximum scores. An analysis of variance showed that all the main effects: T, age, and monaural versus binaural listening were significant. The scores declined with T for all ages. The best scores were obtained by the young adults (27 year olds). The binaural scores were about 5% better than monaural scores. Factors contributing to the results and practical implications for amplification are discussed.

Perception of consonants in reverberation by native and non-native listeners.

Speech perception in reverberation was compared for native English speaking and non‐native listeners. The Modified Rhyme Test was recorded with reverberation times (T) of 0.4, 0.8, and1.2 s. Testing was monaural. The mean word identification scores without reverberation were similar for both groups. With T=0.8 and 1.2 s, non‐native listeners scored 10% lower than the native listeners. These results indicate that non‐native listeners who understand English very well in the absence of reverberation might have difficulty understanding speech in the presence of even moderate reverberation.

Reception of consonants in a classroom as affected by monaural and binaural listening, noise, reverberation, and hearing aids

Reception of consonants was studied with normal‐hearing subjects in a sound‐treated classroom, at reverberation times T ≃0.3 and 0.6 sec, to compare binaural and monaural reception, with and without hearing aids, in the presence of an impulsive noise (16 imp/sec) and a quasisteady noise (a babble of eight voices). The consonants were spoken in words inbedded in a rapidly spoken carrier phrase. The speech and noise sources subtended an angle of 60° on a circle 11 ft in radius centered on the listener, to give a large advantage for binaural reception. Binaural gain was taken as the difference in speech‐to‐noise ratios for 60% correct reception comparing binaural and monaural results. The binaural gain at short reverberation, with unaided listening, was 5 dB in the presence of the babble and 4 dB in the presence of the impulsive noise. The introduction of hearing aids and the increase in reverberation each caused the binaural gain to decrease to 3 dB. The small increase in reverberation caused a substantial ...

Identification of vowels in quiet, noise, and reverberation: Relationships with age and hearing loss

Vowel identification in quiet, noise, and reverberation was tested with 40 subjects who varied in age and hearing level. Stimuli were 15 English vowels spoken in a (b-t) context in a carrier sentence, which were degraded by reverberation or noise (a babble of 12 voices). Vowel identification scores were correlated with various measures of hearing loss and with age. The mean of four hearing levels at 0.5, 1, 2, and 4 kHz, termed HTL4, produced the highest correlation coefficients in all three listening conditions. The correlation with age was smaller than with HTL4 and significant only for the degraded vowels. Further analyses were performed for subjects assigned to four groups on the basis of the amount of hearing loss. In noise, performance of all four groups was significantly different, whereas, in both quiet and reverberation, only the group with the greatest hearing loss performed differently from the other groups. The relationship among hearing loss, age, and number and type of errors is discussed in light of acoustic cues available for vowel identification.

Pitch of tone bursts of changing frequency.

The pitch of tone bursts containing a linear change of frequency, either throughout 100% or for only a portion (5% and 25%) of the total burst duration, was studied. Pitch judgments for the tone bursts with the frequency change throughout the burst duration show that a single pitch can be assigned to the burst as long as the frequency change and duration are not too large. The single‐pitch character of such a glide deteriorates as the product of the burst duration and frequency change increases and seems to follow the change of spectra. For the bursts with short transitions, when the frequency change is not too large, the pitch assigned to the burst changes smoothly from the final to the initial frequency according to the delay of the transition onset. For larger frequency changes, bursts can be matched by either initial or final frequency, a case called separation, as distinguished from the more singular fusion. The change from fusion to separation corresponds to the change from spectra with one maximum ...

Vowel errors in noise and in reverberation by hearing-impaired listeners

The effects of noise and reverberation on the identification of monophthongs and diphthongs were evaluated for ten subjects with moderate sensorineural hearing losses. Stimuli were 15 English vowels spoken in a /b-t/ context, in a carrier sentence. The original tape was recorded without reverberation, in a quiet condition. This test tape was degraded either by recording in a room with reverberation time of 1.2 s, or by adding a babble of 12 voices at a speech-to-noise ratio of 0 dB. Both types of degradation caused statistically significant reductions of mean identification scores as compared to the quiet condition. Although the mean identification scores for the noise and reverberant conditions were not significantly different, the patterns of errors for these two conditions were different. Errors for monophthongs in reverberation but not in noise seemed to be related to an overestimation of vowel duration, and there was a tendency to weight the formant frequencies differently in the reverberation and quiet conditions. Errors for monophthongs in noise seemed to be related to spectral proximity of formant frequencies for confused pairs. For the diphthongs in both noise and reverberation, there was a tendency to judge a diphthong as the beginning monophthong. This may have been due to temporal smearing in the reverberation condition, and to a higher masked threshold for changing compared to stationary formant frequencies in the noise condition.

The influence of talker differences on vowel identification by normal‐hearing and hearing‐impaired listeners

Vowel identification was tested in quiet, noise, and reverberation with 20 normal-hearing subjects and 20 hearing-impaired subjects. Stimuli were 15 English vowels spoken in a /b-t/context by six male talkers. Each talker produced five tokens of each vowel. In quiet, all stimuli were identified by two judges as the intended targets. The stimuli were degraded by reverberation or speech-spectrum noise. Vowel identification scores depended upon talker, listening condition, and subject type. The relationship between identification errors and spectral details of the vowels is discussed.

Pitch of sound bursts with continuous or discontinuous change of frequency

In an earlier study [I. V. Nabělek, A. K. Nabělek, and I. J. Hirsh, J. Acoust. Soc. Am. 48, 536–553 (1970)] of the pitch of a sound burst with two frequencies connected by a linear frequency change (a glide), it was found that the pair of frequencies, initial and final, are sometimes perceptually fused and sometimes perceptually separated. In the present study, the pitch of the same kind of bursts is compared with the pitch bursts in which the glide is supplanted by a pause. The method of adjustment was used. Some differences in the pitch perception of bursts with glides and those with pauses were found. Prolongation of the glide made separation more difficult and fusion easier, while prolongation of the pause made separation easier and fusion more difficult. Prolongation of either the glide or the final frequency of the burst casued the pitch to be shifted toward the final frequency, while the prolongation of the pause (0–40 msec) did not change the pitch. For an explanation of this discrepancy it seems ...

Vowel boundaries for steady‐state and linear formant trajectories

Locations of boundaries and slopes of identification functions were tested for /I-epsilon/ vowel continua with steady-state and linearly changing formant trajectories. In experiment 1, the boundaries and slopes for arbitrarily selected trajectory directions were determined for ten normal-hearing and ten hearing-impaired subjects in three listening conditions: Quiet, noise, and reverberation. The boundaries did not depend upon the group of subjects or the listening condition. A boundary shift was found for stimuli with F1 changing in a downward direction relative to boundaries for stimuli with either only F1 or with both F1 and F2 changing in an upward direction. The slope of the identification function for stimuli with F1 changing in a downward direction was shallower than the slopes for stimuli with steady-state formants or stimuli with F1 changing in an upward direction. The slopes obtained from the hearing-impaired subjects were shallower than those of the normal-hearing subjects and were shallower in noise than in either quiet or reverberation. In experiment 2, boundaries and slopes for the trajectory directions found in the natural vowels /I/ and /epsilon/, F1 changing in an upward direction and F2 in a downward direction, were determined for nine normal-hearing subjects in two listening conditions, quiet and reverberation. The boundary for stimuli with both F1 and F2 changing in directions characteristic for natural vowels was shifted relative to the boundary for stimuli with steady-state formants. The directions of the boundary shifts in experiments 1 and 2 indicated a perceptual emphasis on the initial sections of changing F1 and F2. Sound quality of the end-point /I/ and /epsilon/ stimuli depended upon F1 and F2 trajectories. For both vowels, the best quality judgments were found for the stimuli with natural F1 and F2 trajectory directions. The quality judgments were weakly correlated with the slopes of identification functions, with better quality judgments being associated with steeper slopes.

Comparison of amplification systems in an auditorium

Intelligibility of speech at two positions in a large auditorium was compared for the public address system (PA) and two assistive listening systems: Frequency modulation of radio frequencies (FM) and modulation of infrared light waves (IR). Listening groups were: normal-hearing adults, hearing-impaired, hearing aid users, elderly, and non-native. Word-identification scores were obtained with the Modified Rhyme Tests. Analysis of variance indicated that the main effects of systems, groups, and listening position were significant. Also significant were the two-way interactions. For all groups, the assistive listening systems provided better scores than the PA system. The difference between the two systems was statistically significant, but very small. It can be concluded that both listening systems provide improved speech intelligibility for various types of listeners.