Speech Intelligibility In Noisy Environments Research Articles

Spectral Dynamics Recovery for Enhanced Speech Intelligibility in Noise

Speech intelligibility in noisy environments decreases with an increase in the noise power. We hypothesize that the differences of subsequent short-term spectra of speech, which we collectively refer to as the speech spectral dynamics, can be used to characterize speech intelligibility. We propose a distortion measure to characterize the deviation of the dynamics of the noisy modified speech from the dynamics of natural speech. Optimizing this distortion measure, we derive a parametric relationship between the signal band-power before and after modification. The parametric nature of the solution ensures adaptation to the noise level, the speech statistics and a penalty on the power gain. A multi-band speech modification system based on the single-band optimal solution is designed under a total signal power constraint and evaluated in selected noise conditions. The results indicate that the proposed approach compares favorably to a reference method based on optimizing a measure of the speech intelligibility index. Very low computational complexity and high intelligibility gain make this an attractive approach for speech modification in a wide range of application scenarios.

Effect of Speech Degradation on Top-Down Repair: Phonemic Restoration with Simulations of Cochlear Implants and Combined Electric–Acoustic Stimulation

The brain, using expectations, linguistic knowledge, and context, can perceptually restore inaudible portions of speech. Such top-down repair is thought to enhance speech intelligibility in noisy environments. Hearing-impaired listeners with cochlear implants commonly complain about not understanding speech in noise. We hypothesized that the degradations in the bottom-up speech signals due to the implant signal processing may have a negative effect on the top-down repair mechanisms, which could partially be responsible for this complaint. To test the hypothesis, phonemic restoration of interrupted sentences was measured with young normal-hearing listeners using a noise-band vocoder simulation of implant processing. Decreasing the spectral resolution (by reducing the number of vocoder processing channels from 32 to 4) systematically degraded the speech stimuli. Supporting the hypothesis, the size of the restoration benefit varied as a function of spectral resolution. A significant benefit was observed only at the highest spectral resolution of 32 channels. With eight channels, which resembles the resolution available to most implant users, there was no significant restoration effect. Combined electric–acoustic hearing has been previously shown to provide better intelligibility of speech in adverse listening environments. In a second configuration, combined electric–acoustic hearing was simulated by adding low-pass-filtered acoustic speech to the vocoder processing. There was a slight improvement in phonemic restoration compared to the first configuration; the restoration benefit was observed at spectral resolutions of both 16 and 32 channels. However, the restoration was not observed at lower spectral resolutions (four or eight channels). Overall, the findings imply that the degradations in the bottom-up signals alone (such as occurs in cochlear implants) may reduce the top-down restoration of speech.

Possible implications of interaural mismatch in the place-of-stimulation on spatial release from masking in cochlear implant listeners

Recent research suggests that bilateral cochlear implant (CI) users have improved speech intelligibility in noisy environments compared to unilateral CI users. This may not be surprising given that in normal hearing (NH) listeners, binaural hearing allows them to localize sounds and this ability allows them to benefit from a spatial release from masking (SRM). However, SRM benefits are much less in CI users and vary amongst users. This may be due to the interaural mismatch in the place-of-stimulation across the ears in CI users and occurs due to differences in neural survival and electrode implantation depth across the ears, leading to different parts of the cochlea being excited by electrodes of the same number. Data will be presented that shows that with increasing interaural mismatch, CI users typically heard lateralized or multiple sounds. In some CI users, interaural mismatches greater than 3 mm leads to an inability to use binaural cues. These effects may impact a CI user's ability to obtain SRM. Pr...

Soundscape analysis: Need for (automatic) source separation.

The use of psychoacoustics for soundscape analysis is imperative to predict the soundscape from an acoustical point of view. Psychoacoustic parameters as functions of intensity, time structure, and spectral content play an important role with respect to several sensations and yield information with greater differentiation than usually applied indicators within the community noise context. But, with respect to a comprehensive analysis of a soundscape, the exact source constellation must be known. Based on the performance of the human hearing system including intelligent signal processing, a listener can easily focus on a certain source and suppress the noise of other sources, which considerably influences the general appreciation of the whole soundscape. For example, this ability is permanently used to improve speech intelligibility in noisy environments. Therefore, an acoustical soundscape analysis should not just deal with the overall noise, but rather the (psycho-)acoustical properties of the different sources present in a soundscape must be investigated separately. Different methods are conceivable in realizing source separation in complex noise scenarios. The paper will present a few case studies demonstrating the opportunities in separating the contributions of several sound sources within a soundscape.

Aplicação do teste de lateralização sonora em idosos

The ability to determine the direction of a sound source is based on the fact that sounds reach both cars at different times, phase, intensity and/or frequency. The perception of a sound source favors speech intelligibility in noisy environments. To identify the minimum time of interaural delay--produces lateralization to the car which the stimulus reached first--through ascendant and descendent techniques, using the Sound Lateralization Test in elderly individuals with normal hearing thresholds in the frequencies which are most important for speech comprehension. The Lateralization Test was used in 30 individuals with ages above 60 years, who presented hearing thresholds up to 25 dBHL in 500, 1000 and 2000 Hz and with no air-bone gap. Mean times of interaural delay in sound lateralization were: a) ascending technique: 125.56 sec. (female) and 83.61 sec. (male); b) descending technique: 95.06 sec. (female) and 61.68 sec (male). There is no difference between the mean time of interaural delay in sound lateralization obtained with the ascending or descending technique regarding the variable initial tested ear (right or left ear); the mean time of interaural delay in sound lateralization is smaller in males, when considering both ascendant and descendent techniques; the mean time of interaural delay in sound lateralization obtained with the descendent technique is smaller than that obtained with the ascendant technique; individuals who present hearing losses beginning at 3000 Hz have smaller mean times of interaural delay in sound lateralization than normal hearing individuals in both techniques.

Evaluation of auditory processing disorders after whiplash injury

Whiplash patients often have many subjective complaints, such as headaches, concentration difficulties, fatigue, neck pain and vertigo. Objective assessment of these complaints is difficult and neurological and neuropsychological signs of damage are not obvious. Other complaints frequently expressed after whiplash injury are diminished speech intelligibility in noisy environments and decreased tolerance to ‘loud’ sounds. In the present study, the latter complaints were evaluated with behavioural auditory tests. A test battery for auditory processing disorders was administered to 22 chronic whiplash patients with normal peripheral hearing. The test battery consists of seven tests: a sentences-in-noise test, pattern recognition tests, words-in-noise test, dichotic digit test, filtered speech test, binaural fusion test and backward masking tests. The uncomfortable loudness level (UCL) was also assessed using speech material. In addition, a questionnaire on auditory handicap was administered. The results were...

SVD-Based Optimal Filtering for Noise Reduction in Dual Microphone Hearing Aids: A Real Time Implementation and Perceptual Evaluation

In this paper, the first real-time implementation and perceptual evaluation of a singular value decomposition (SVD)-based optimal filtering technique for noise reduction in a dual microphone behind-the-ear (BTE) hearing aid is presented. This evaluation was carried out for a speech weighted noise and multitalker babble, for single and multiple jammer sound source scenarios. Two basic microphone configurations in the hearing aid were used. The SVD-based optimal filtering technique was compared against an adaptive beamformer, which is known to give significant improvements in speech intelligibility in noisy environment. The optimal filtering technique works without assumptions about a speaker position, unlike the two-stage adaptive beamformer. However this strategy needs a robust voice activity detector (VAD). A method to improve the performance of the VAD was presented and evaluated physically. By connecting the VAD to the output of the noise reduction algorithms, a good discrimination between the speech-and-noise periods and the noise-only periods of the signals was obtained. The perceptual experiments demonstrated that the SVD-based optimal filtering technique could perform as well as the adaptive beamformer in a single noise source scenario, i.e., the ideal scenario for the latter technique, and could outperform the adaptive beamformer in multiple noise source scenarios.

Speech recognition in noise for cochlear implantees with a two-microphone monaural adaptive noise reduction system.

In this study the performance of a noise reduction strategy applied to cochlear implants is evaluated. The noise reduction strategy is based on a 2-channel adaptive filtering strategy using two microphones in a single behind-the-ear hearing aid. Four adult LAURA cochlear implant users (Peeters et al., 1993) took part in the experiments. The tests included identification of monosyllabic CVC (consonant-vowel-consonant) words and measurements of the speech reception threshold (SRT) of lists of numbers, in background noise presented at 90 degrees relative to the 0 degrees frontal direction of the speech. Percent correct phoneme scores for the CVC words at signal to noise ratios (SNRs) of -5, 0, and +5 dB in steady speech-weighted noise at 60 dB SPL and SRTs for numbers in speech-weighted steady and nonsteady ICRA noise were both obtained in conditions with and without the noise reduction pre-processing. Physical SNR improvements of the noise reduction system are evaluated as well, as a function of the direction of the noise source. Highly significant improvements in speech understanding, corresponding on average to an SNR improvement of about 10 dB, were observed with this 2-channel adaptive filtering noise reduction strategy using both types of speech-noise test materials. These perceptual evaluations agree with physical evaluations and simulations of this noise reduction strategy. Taken together, these data demonstrate that cochlear implantees may increase their speech intelligibility in noisy environments with the use of multimicrophone noise reduction systems.

The impact of head angle on monaural and binaural performance with directional and omnidirectional hearing aids.

To evaluate the impact of head turn and monaural and binaural fittings on the sentence reception thresholds of hearing-impaired listeners wearing directional and omnidirectional hearing aids. Sentence reception thresholds were measured for 20 listeners fit monaurally and binaurally with behind-the-ear hearing aids set in both directional and omnidirectional modes. All listeners exhibited symmetrical, sloping, sensorineural hearing loss. The aided performance across these four fittings was evaluated for three different head and body angles. The three angles reflected body turns of 0 degrees, 15 degrees, and 30 degrees as measured relative to the primary sound source, with 0 degrees denoting the listener directly facing the sound source. Listeners were instructed to keep their heads in a fixed horizontal position and turn their heads and bodies to face visual targets at the three test angles. Sentences from the Hearing in Noise Test presented with a background of five, spatially separated, uncorrelated samples of cafeteria noise served as test material. All testing was performed in a moderately reverberant (Rt = 631 msec) "living room" environment. Participants generally performed significantly better when fit with directional versus omnidirectional hearing aids, and when fit binaurally versus monaurally across test conditions. The measured "binaural advantage" was reduced with increasing head angle. Participants performed significantly better with a 30 degree head angle than when directly facing the primary speaker. This "head turn advantage" was most prominent for monaural (versus binaural) conditions. Binaural and head turn advantages were not significantly different across directional and omnidirectional modes. These data provide additional support for the use of directional hearing aids and binaural amplification to improve speech intelligibility in noisy environments. The magnitude of these advantages was similar to that reported in previous investigations. The data also showed that hearing aid wearers achieved significantly better speech intelligibility in noise by turning their heads and bodies to a position in which they were not directly facing the sound source. This head turn advantage was in good agreement with the increase in Directivity Index with head turn and reflected the fact that hearing aids are generally most sensitive to sounds arriving from angles other than directly in front of the hearing aid wearer. Although these data suggest that many monaural hearing aid wearers may significantly improve speech intelligibility in noise through the use of head turn, the interaction between this advantage and the potential loss of visual cues with head turn is unknown.

Speech Intelligibility Enhancement by Interaural Magnification.

Hearing-impaired persons suffer from loss of speech intelligibility in noisy environments as well as from a decrease in binaural performance (e.g., interaural time and intensity discrimination). In order to improve speech intelligibility for spatially separated signal and noise sources by compensating for the reduced binaural performance, we implemented an algorithm increasing binaural dissimilarity on a digital signal processor. This algorithm is a modification of the proposal by Durlach & Pang (J. Acoust. Soc. Am. 1986; 80: 1849-1850). Speech discrimination experiments were performed under simulated spatial conditions with recordings of the speech material and the interfering noise source using a dummy head. With increasing complexity of the spatial masking condition, the binaural advantage as well as the benefits from the algorithm decreased for normal listeners. For four sensorineurally hearing-impaired listeners, only one spatial condition was tested. In addition, a battery of binaural tests (binaural masking level difference, interaural time and intensity discrimination) was performed. The results indicate that the benefits from the signal-processing technique are correlated with the remaining binaural performance.