Noise reduction results of an adaptive filtering technique for dual-microphone behind-the-ear hearing aids

OBJECTIVE: The performance of an adaptive beam-former in a 2-microphone, behind-the-ear hearing aid for speech understanding in noisy environments was evaluated. Physical and perceptual evaluations were carried out. This was the first large-scale test of a wearable real-time implementation of this algorithm. The main perceptual research questions of this study were related to the influence on the noise reduction performance of (1) the spectro-temporal character of the jammer sound, (2) the jammer sound scene, (3) hearing impairment, and (4) the basic microphone configuration in the hearing aid. Four different speech materials were used for the perceptual evaluations. All tests were carried out in an acoustical environment comparable to living room reverberation. DESIGN: The adaptive beamformer was implemented in Audallion, a small, body-worn processor, linked to a Danasound 2-microphone behind-the-ear aid. The strategy was evaluated physically in different acoustical environments. Using speech reception threshold (SRT) measurements, the processing was evaluated perceptually and the different research questions addressed with three groups of subjects. Groups I, II, and III consisted of 10 normal-hearing, 5 hearing-impaired, and 7 normal-hearing persons, respectively. The tests were carried out in three spectro-temporally different jammer sounds (unmodulated and modulated speech weighted noise, multitalker babble) and in three different noise scenarios (single noise source at 90 degrees, noise sources at 90 degrees and 270 degrees relative to speaker position, diffuse noise scene). Two microphone configurations were compared: a device equipped with two omnidirectional microphones and a device equipped with one hardware directional and one omnidirectional microphone. In each of these conditions, the adaptive beamformer and the directional and omnidirectional microphone configurations were tested. RESULTS: The improvement in signal-to-noise ratio from the use of the adaptive beamformer did not depend on the spectro-temporal character of the jammer sounds and the speech materials used, although the absolute levels of the SRTs varied appreciably for different speech-noise combinations. The performance of the adaptive noise reduction depended on the jammer sound scene. CONCLUSIONS: No difference in signal-to-noise ratio improvement was observed between hearing-impaired and normal-hearing listeners, although individual SRT levels may differ. On average, an SRT improvement of 7.7 and 3.9 dB for a single noise source at 90 degrees and 5.9 and 3.4 dB for two noise sources at 90 degrees and 270 degrees was obtained for both normal-hearing and hearing-impaired listeners, using the adaptive beamformer and the directional microphone, respectively, relative to the omnidirectional microphone signal. In diffuse noise, only small improvements were obtained.     

Using hearing aid adaptive directional microphones to enhance cochlear implant performance

The goal of this study was to investigate whether adaptive microphone directionality could enhance cochlear implant performance. Speech stimuli were created by fitting a digital hearing aid with programmable omnidirectional (OM), fixed directional (FDM), or adaptive directional (ADM) microphones to KEMAR, and recording the hearing aid output in three noise conditions. The first condition simulated a diffused field with noise sources from five stationary locations, whereas the second and third condition represented one or three non-stationary locations in the back hemifield of KEMAR. Speech was always presented to 0° azimuth and the overall signal-to-noise ratio (SNR) was +5 dB in the sound field. Eighteen postlingually deafened cochlear implant users listened to the recorded test materials via the direct audio input of their speech processors. Their speech recognition ability and overall sound quality preferences were assessed and the correlation between the amount of noise reduction and the improvement in speech recognition were calculated. The results indicated that ADM yielded significantly better speech recognition scores and overall sound quality preference than FDM and OM in all three noise conditions and the improvement in speech recognition scores was highly correlated with the amount of noise reduction. Factors influencing the noise level are discussed.     

Speech intelligibility in noisy environments with one- and two-microphone hearing aids

In this study speech intelligibility in background noise was evaluated with 10 binaural hearing-aid users for hearing aids with one omnidirectional microphone and a hearing aid with a two-microphone configuration (enabling an omnidirectional as well as a directional mode). Signal-to-noise ratio (SNR) measurements were carried out for three different types of background noise (speech-weighted noise, traffic noise and restaurant noise) and two kinds of speech material (bisyllabic word lists and sentences). The average SNR improvement of the directional microphone configuration relative to the omnidirectional one was 3.4 dB for noise presented from 90 degrees azimuth. This improvement was independent of the specific type of noise and speech material, indicating that one speech-in-noise condition may yield enough relevant information in the evaluation of directional microphones and speech understanding in noise.     

正常听力受试者佩戴不同组合全向性与方向性麦克风的效果比较

目的 比较噪声环境下全向性麦克风与自适应方向性麦克风的不同组合佩戴方式对听力正常成年人言语识别率的影响,从而选择最佳的组合佩戴方式.方法 选择20例(40耳)听力正常青年人(男、女各10例)分别按照双耳全向性麦克风模式(组合1),双耳自适应方向性麦克风模式(组合2),一耳全向性麦克风、一耳自适应麦克风模式(组合3)3种方式,在信噪比变化的漫射声场中进行言语识别率测试,从而进行助听效果的评估.结果 组合1、2、3三种方式测出的L50值(50%言语识别率的信噪比)分别为-3.55±2.37 dB,-7.15±2.18 dB,-5.40±2.35 dB,三者之间两两比较差异均有显著统计学意义(P<0.05).结论 噪声环境下无论双耳佩戴自适应方向性麦克风模式还是一耳佩戴自适应方向性麦克风、另一耳佩戴全向性麦克风,其言语识别能力均高于双耳佩戴全向性麦克风模式,且双耳佩戴自适应方向性麦克风模式的言语识别率高于一耳自适应麦克风、一耳全向性麦克风模式.     

Effect of signal-to-noise ratio on directional microphone benefit and preference

This study examined speech intelligibility and preferences for omnidirectional and directional microphone hearing aid processing across a range of signal-to-noise ratios (SNRs). A primary motivation for the study was to determine whether SNR might be used to represent distance between talker and listener in automatic directionality algorithms based on scene analysis. Participants were current hearing aid users who either had experience with omnidirectional microphone hearing aids only or with manually switchable omnidirectional/directional hearing aids. Using IEEE/Harvard sentences from a front loudspeaker and speech-shaped noise from three loudspeakers located behind and to the sides of the listener, the directional advantage (DA) was obtained at 11 SNRs ranging from -15 dB to +15 dB in 3 dB steps. Preferences for the two microphone modes at each of the 11 SNRs were also obtained using concatenated IEEE sentences presented in the speech-shaped noise. Results revealed that a DA was observed across a broad range of SNRs, although directional processing provided the greatest benefit within a narrower range of SNRs. Mean data suggested that microphone preferences were determined largely by the DA, such that the greater the benefit to speech intelligibility provided by the directional microphones, the more likely the listeners were to prefer that processing mode. However, inspection of the individual data revealed that highly predictive relationships did not exist for most individual participants. Few preferences for omnidirectional processing were observed. Overall, the results did not support the use of SNR to estimate the effects of distance between talker and listener in automatic directionality algorithms.     

Investigating Speech Recognition and listening effort with different device configurations in adult cochlear implant users

Objectives: The purpose of this study was to investigate speech recognition in noise and listening effort among a group of adults with cochlear implants (CIs). Two main research questions were addressed. First, what are the effects of omni versus directional microphone configuration on speech recognition and listening effort for noisy conditions? Second, what is the effect of unilateral versus bimodal or bilateral CI listening on speech recognition and listening effort in noisy conditions?

Design: Sixteen adults (mean age 58 years) with CIs participated. Listening effort was measured using a dual-task paradigm and also using a self-reported rating of difficulty scale. In the dual-task measure, participants were asked to repeat monosyllabic words while at the same time press a button in response to a visual stimulus. Participants were tested in two baseline conditions (speech perception alone and visual task alone) and in the following experimental conditions: (1) quiet with an omnidirectional microphone, (2) noise with an omnidirectional microphone, (3) noise with a directional microphone, and (4) noise with a directional microphone and with a second sided CI or hearing aid. When present, the noise was fixed with a +5?dB signal-to-noise ratio. After each listening condition, the participants rated the degree of listening difficulty.

Results: Changing the microphone from omni to directional mode significantly enhanced speech recognition in noise performance. There were no significant changes in speech recognition between the unilateral and bimodal/bilateral CI listening conditions. Listening effort, as measured by reaction time, increased significantly between the baseline and omnidirectional quiet listening condition though did not change significantly across the remaining listening conditions. Self-perceived listening effort revealed a greater effort for the noisy conditions, and reduced effort with the move from an omni to a directional microphone.

Conclusions: Directional microphones significantly improve speech in noise recognition over omnidirectional microphones and allowed for decreased self-perceived listening effort. The dual task used in this study failed to show any differences in listening effort across the experimental conditions and may not be sensitive enough to detect changes in listening effort.     

Better speech perception in noise with an assistive multimicrophone array for hearing AIDS

OBJECTIVE: To evaluate the improvement in speech intelligibility in noise obtained with an assistive real-time fixed endfire array of bidirectional microphones in comparison with an omnidirectional hearing aid microphone in a realistic environment. DESIGN: The microphone array was evaluated physically in anechoic and reverberant conditions. Perceptual tests of speech intelligibility in noise were carried out in a reverberant room, with two types of noise and six different noise scenarios with single and multiple noise sources. Ten normal-hearing subjects and 10 hearing aid users participated. The speech reception threshold for sentences was measured in each test setting for the omnidirectional microphone of the hearing aid and for the hearing aid in combination with the array with one and three active microphones. In addition, the extra improvement of five active array microphones, relative to three, was determined in another group of 10 normal-hearing listeners. RESULTS: Improvements in speech intelligibility in noise obtained with the array relative to an omnidirectional microphone depend on noise scenario and subject group. Improvements up to 12 dB for normal-hearing and 9 dB for hearing-impaired listeners were obtained with three active array microphones relative to an omnidirectional microphone for one noise source at 90 degrees . For three uncorrelated noise sources at 90 degrees, 180 degrees, and 270 degrees, improvements of approximately 9 dB and 6 dB were obtained for normal-hearing and hearing-impaired listeners, respectively. Even with a single noise source at 45 degrees, benefits of 4 dB were achieved in both subject groups. Five active microphones in the array can provide an additional improvement at 45 degrees of approximately 1 dB, relative to the three-microphone configuration for normal-hearing listeners. CONCLUSIONS: These improvements in signal-to-noise ratio can be of great benefit for hearing aid users, who have difficulties with speech understanding in noisy environments.     

Evaluation of the benefit for cochlear implantees of two assistive directional microphone systems in an artificial diffuse noise situation

OBJECTIVE: People with cochlear implants have severe problems with speech understanding in noisy surroundings. This study evaluates and quantifies the effect of two assistive directional microphone systems compared to the standard headpiece microphone on speech perception in quiet surroundings and in background noise, in a laboratory setting developed to reflect a situation whereby the listener is disturbed by a noise with a mainly diffuse character due to many sources in a reverberant room. DESIGN: Thirteen postlingually deafened patients, implanted in the Leiden University Medical Centre with the Clarion CII device, participated in the study. An experimental set-up with 8 uncorrelated steady-state noise sources was used to test speech perception on monosyllabic words. Each subject was tested with a standard headpiece microphone, and the two assistive directional microphones, TX3 Handymic by Phonak and the Linkit array microphone by Etymotic Research. Testing was done in quiet at a level of 65 dB SPL and with decreasing signal-to-noise ratios (SNR) down to -15 dB. RESULTS: Using the assistive directional microphones, speech recognition in background noise improved substantially and was not affected in quiet. At an SNR of 0 dB, the average CVC scores improved from 45% for the headpiece microphone to 67% and 62% for the TX3 Handymic and the Linkit respectively. Compared to the headpiece, the Speech Reception Threshold (SRT) improved by 8.2 dB SNR and 5.9 dB SNR for the TX3 Handymic and the Linkit respectively. The gain in SRT for TX3 Handymic and Linkit was neither correlated to the SRT score with headpiece nor the duration of CI-use. CONCLUSION: The speech recognition test in background noise showed a clear benefit from the assistive directional microphones for cochlear implantees compared to the standard microphone. In a noisy environment, the significant benefit from these assistive device microphones may allow understanding of speech with greater ease.     

Speech recognition and comfort using hearing instruments with adaptive directional characteristics in asymmetric listening conditions

OBJECTIVE: Hearing instruments with adaptive directional microphone systems attempt to maximize speech-to-noise ratio (SNR) and thereby improve speech recognition in noisy backgrounds. When instruments with adaptive systems are fitted bilaterally, there is the potential for adverse effects as they operate independently and may give confusing cues or disturbing effects. The present study compared speech recognition performance in 16 listeners fitted bilaterally with the Phonak Claro hearing instrument using omni-directional, fixed directional, and adaptive directional microphone settings as well as mixed microphone settings (an omni-directional microphone on one side and an adaptive directional microphone on the other). DESIGN: Under anechoic conditions, speech was always presented from a loudspeaker directly in front of the listener (0 degree azimuth) whereas noise was presented from one or two loudspeakers arranged either symmetrically (0, 180, 90 + 270 degrees) or asymmetrically (170 + 240 degrees and 120 + 190 degrees) in the horizontal plane. Adaptive sentence recognition in noise measurement was supplemented by quality ratings. RESULTS: With symmetrical omni-directional settings (Omni/Omni), performance was poorer than a control group of 14 listeners with normal hearing tested unaided: Aided listeners required 4.3 dB more favorable SNR for criterion performance. In all loudspeaker arrangements in which directional characteristics could be exploited, performance with symmetrical adaptive microphones (Adapt/Adapt) was similar to the control group. The mixed microphone settings did not appear to confer any particular disadvantage for speech recognition from their asymmetric nature, always giving scores significantly better than Omni/Omni. Quality rating scores were consistent with speech recognition performance, showing benefits in terms of clarity and comfort for the Adapt/Adapt and Fixed/Fixed microphone conditions over the Omni/Omni and mixed microphone conditions wherever directional characteristics could be used. Similarly, the mixed microphone conditions were rated more comfortable and quieter for the noise than Omni/Omni. CONCLUSIONS: It is concluded that bilateral hearing instruments with adaptive directional microphones confer benefits in terms of speech recognition in noise and sound quality. Independence of the two adaptive control systems does not appear to cause untoward effects.     

Evaluation of an adaptive,directional-microphone hearing aid

The effectiveness of adaptive directional processing for improvement of speech recognition in comparison to non-adaptive directional and omni-directional processing was examined across four listening environments intended to simulate those found in the real world. The test environment was a single, moderately reverberant room with four loudspeaker configurations: three with fixed discrete noise source positions and one with a single panning noise source. Sentence materials from the Hearing in Noise Test (HINT) and Connected Speech Test (CST) were selected as test materials. Speech recognition across all listening conditions was evaluated for 20 listeners fitted binaurally with Phonak Claro behind-the-ear (BTE) style hearing aids. Results indicated improved speech recognition performance with adaptive and non-adaptive directional processing over that measured with the omnidirectional processing across all four listening conditions. While the magnitudes of directional benefit provided to subjects listening in adaptive and fixed directional modes were similar in some listening environments, a significant speech recognition advantage was measured for the adaptive mode in specific conditions. The advantage for adaptive over fixed directional processing was most prominent when a competing noise was presented from the listener's sides (both fixed and panning noise conditions), and was partially predictable from electroacoustically measured directional pattern data.     

Effects of frequency modulation (FM) transmitter microphone directivity on speech perception in noise

Frequency modulation (FM) technology can significantly improve the speech perception ability of individuals with sensorineural hearing loss (SNHL) in background noise. Previous investigations have demonstrated that the microphone design of the FM transmitter can have a significant impact on this improved speech perception. The purpose of this investigation was to compare 3 types of FM transmitter microphone designs: (a) wide angle (omnidirectional microphone), which amplifies sounds coming from all directions around the microphone equally; (b) zoom (1 directional microphone), which provides less amplification to signals coming from the rear, and (c) superzoom (2 directional microphones), which provides less amplification to signals originating from the rear and the sides. Fifteen adults with bilateral slight to moderately severe SNHL participated. Speech perception was assessed using the Hearing in Noise Test (M. Nilsson, S. Soli, and J. Sullivan, 1994). Speech spectrum shaped noise served as the noise competition. Results revealed that the best speech perception in noise was obtained when the FM transmitter was used in the zoom setting. The poorest performance was obtained when the FM transmitter was in the wide-angle mode. The clinical implications of these results are discussed.     

A directional remote-microphone for bimodal cochlear implant recipients

Abstract

To evaluate whether speech recognition in noise differs according to whether a wireless remote microphone is connected to just the cochlear implant (CI) or to both the CI and to the hearing aid (HA) in bimodal CI users. The second aim was to evaluate the additional benefit of the directional microphone mode compared with the omnidirectional microphone mode of the wireless microphone. This prospective study measured Speech Recognition Thresholds (SRT) in babble noise in a ‘within-subjects repeated measures design’ for different listening conditions. Eighteen postlingually deafened adult bimodal CI users. No difference in speech recognition in noise in the bimodal listening condition was found between the wireless microphone connected to the CI only and to both the CI and the HA. An improvement of 4.1?dB was found for switching from the omnidirectional microphone mode to the directional mode in the CI only condition. The use of a wireless microphone improved speech recognition in noise for bimodal CI users. The use of the directional microphone mode led to a substantial additional improvement of speech perception in noise for situations with one target signal.     

Multi-microphone technology for severe-to-profound hearing loss

In this study the potential benefit of hearing instruments with multi-microphone technology was investigated in laboratory and in field tests for users with severe-to-profound hearing loss. Twenty-one experienced hearing aid users were fitted with high-power multi-microphone hearing instruments (Phonak PowerZoom P4 AZ). The following evaluations were performed: (i) adaptive speech test (SRT for HSM sentence test) in quiet and in noise with their own instrument and the test instrument in the omnidirectional (basic program) and directional mode (party noise profound+zoom algorithm). (ii) Paired comparisons of loudness, sound quality and speech intelligibility for both the omni and zoom program. (iii) Questionnaires on satisfaction and self-assessment of communication in different listening conditions (Oldenburg Inventory). Only 10 subjects achieved 50% correct (SRT) on the sentence test in noise (speech 0 degrees/noise 180 degrees) with both their own instrument and the test instrument in the omnidirectional mode. However, 15 subjects succeeded in the SRT measurement in the directional mode. The average SRT improvement of the directional over the omnidirectional mode was 13.7 dB. Loudness was judged 'medium loud' for both listening programs. Sound quality and intelligibility were rated significantly better for the zoom program. Compared to their own instrument users' satisfaction with the test instrument was significantly higher, especially in noisy listening situations.     

Improving speech intelligibility in background noise with an adaptive directional microphone

Omnidirectional, supercardioid, and adaptive directional microphones (ADM) were evaluated in combination with the ADRO amplification scheme for eight participants with moderate sloping hearing losses. The ADM produced better speech perception scores than the other two microphones in all noise conditions. Participants performed the Hearing in Noise Test sentences at -4.5 dB SNR or better, which is similar to the level achievable with normal hearing. The Speech, Spatial and Qualities of Hearing Scale indicated no disadvantages of using the ADM relative to the omnidirectional microphone in real-life situations. The ADM was preferred over the omnidirectional microphone in 54% of situations, compared to 17% preferences for the omnidirectional microphone, and 29% no preference. The combination of the ADM to improve SNR, and ADRO to keep the signal output comfortable and audible provided near-normal hearing performance for people with moderate hearing loss. The ADM is the recommended microphone configuration for ADRO hearing aids.     

Noise reduction technologies implemented in head-worn preprocessors for improving cochlear implant performance in reverberant noise fields

The purpose of this study was to investigate whether a multichannel adaptive directional microphone and a modulation-based noise reduction algorithm could enhance cochlear implant performance in reverberant noise fields. A hearing aid was modified to output electrical signals (ePreprocessor) and a cochlear implant speech processor was modified to receive electrical signals (eProcessor). The ePreprocessor was programmed to flat frequency response and linear amplification. Cochlear implant listeners wore the ePreprocessor-eProcessor system in three reverberant noise fields: 1) one noise source with variable locations; 2) three noise sources with variable locations; and 3) eight evenly spaced noise sources from 0° to 360°. Listeners' speech recognition scores were tested when the ePreprocessor was programmed to omnidirectional microphone (OMNI), omnidirectional microphone plus noise reduction algorithm (OMNI?+?NR), and adaptive directional microphone plus noise reduction algorithm (ADM?+?NR). They were also tested with their own cochlear implant speech processor (CI_OMNI) in the three noise fields. Additionally, listeners rated overall sound quality preferences on recordings made in the noise fields. Results indicated that ADM+NR produced the highest speech recognition scores and the most preferable rating in all noise fields. Factors requiring attention in the hearing aid-cochlear implant integration process are discussed.     

The effects of changes in head angle on auditory and visual input for omnidirectional and directional microphone hearing aids

Improving the signal-to-noise ratio (SNR) for individuals with hearing loss who are listening to speech in noise provides an obvious benefit. Although binaural hearing provides the greatest advantage over monaural hearing in noise, some individuals with symmetrical hearing loss choose to wear only one hearing aid. The present study tested the hypothesis that individuals with symmetrical hearing loss fit with one hearing aid would demonstrate improved speech recognition in background noise with increases in head turn. Fourteen individuals were fit monaurally with a Starkey Gemini in-the-ear (ITE) hearing aid with directional and omnidirectional microphone modes. Speech recognition performance in noise was tested using the audiovisual version of the Connected Speech Test (CST v.3). The test was administered in auditory-only conditions as well as with the addition of visual cues for each of three head angles: 0 degrees, 20 degrees, and 40 degrees. Results indicated improvement in speech recognition performance with changes in head angle for the auditory-only presentation mode at the 20 degrees and 40 degrees head angles when compared to 0 degrees. Improvement in speech recognition performance for the auditory + visual mode was noted for the 20 degrees head angle when compared to 0 degrees. Additionally, a decrement in speech recognition performance for the auditory + visual mode was noted for the 40 degrees head angle when compared to 0 degrees. These results support a speech recognition advantage for listeners fit with one ITE hearing aid listening in a close listener-to-speaker distance when they turn their head slightly in order to increase signal intensity.     

Comparisons of speech recognition in noise by mildly-to-moderately hearing-impaired children using hearing aids and FM systems

Four hearing aid arrangements (monaural-omnidirectional, monaural-directional, binaural-omnidirectional, binaural-directional) and a number of FM system-personal hearing aid combinations (including direct input, neck loop, and silhouette inductor--monaural and binaural--and environmental microphone on and off) were evaluated in a school classroom on nine children with mild-to-moderate sensorineural hearing losses. Two measures of speech recognition in noise were employed. First, the signal-to-noise ratio (S/N) yielding 50% identification of spondees was determined using a simple up-down adaptive procedure. Second, word recognition scores were obtained for three amplification arrangements at two different S/Ns (+6 and +15 dB). The average FM advantage over a personal hearing aid was equivalent to a 15-dB improvement in S/N. Activation of the hearing aid microphone caused most of the FM advantage to disappear. The benefit offered by the FM system decreased as the environmental S/N increased but remained significant even at +15 dB. Significant improvement also was found with the use of directional as compared to omnidirectional microphones, both in the hearing aids and FM teacher microphone.     

Quantification of directional benefit across different polar response patterns

The purpose of this study was to assess the relationship between the directivity of a directional microphone hearing aid and listener performance. Hearing aids were fit bilaterally to 19 subjects with sensorineural hearing loss, and five microphone conditions were assessed: omnidirectional, cardioid, hypercardioid, supercardioid, and "monofit," wherein the left hearing aid was set to omnidirectional and the right hearing aid to hypercardioid. Speech perception performance was assessed using the Hearing in Noise Test (HINT) and the Connected Speech Test (CST). Subjects also assessed eight domains of sound quality for three stimuli (speech in quiet, speech in noise, and music). A diffuse soundfield system composed of eight loudspeakers forming the corners of a cube was used to output the background noise for the speech perception tasks and the three stimuli used for sound quality judgments. Results indicated that there were no significant differences in the HINT or CST performance, or sound quality judgments, across the four directional microphone conditions when tested in a diffuse field. Of particular interest was the monofit condition: Performance on speech perception tests was the same whether one or two directional microphones were used.