Directional Microphone System Research Articles

AutoAdaptive: A Noise Level-Sensitive Beamformer for MED EL Cochlear Implant Patients.

When cochlear implant (CI) listeners use a directional microphone or beamformer system to improve speech understanding in noise, the gain in understanding for speech presented from the front of the listener coexists with a decrease in speech understanding from the back. One way to maximize the usefulness of these systems is to keep a microphone in the omnidirectional mode in low noise and then switch to directional mode in high noise. The purpose of this experiment was to assess the levels of speech understanding in noise allowed by a new signal processing algorithm for MED EL CIs, AutoAdaptive, which operates in the manner described previously. Seven listeners fit with bilateral CIs were tested in a simulation of a crowded restaurant with speech presented from the front and from the back at three noise levels, 45, 55, and 65 dB SPL. The listeners were seated in the middle of an array of eight loudspeakers. Sentences from the AzBio sentence lists were presented from loudspeakers at 0 or 180° azimuth. Restaurant noise at 45, 55, and 65 dB SPL was presented from all eight loudspeakers. The speech understanding scores (words correct) were subjected to a two-factor (speaker location and noise level), repeated measures, analysis of variance with posttests. The analysis of variance showed a main effect for level and location and a significant interaction. Posttests showed that speech understanding scores from front and back loudspeakers did not differ significantly at the 45- and 55-dB noise levels but did differ significantly at the 65-dB noise level-with increased scores for signals from the front and decreased scores for signals from the back. The AutoAdaptive feature provides omnidirectional benefit at low noise levels, i.e., similar levels of speech understanding for talkers in front of, and in back of, a listener and beamformer benefit at higher noise levels, i.e., increased speech understanding for signals from in front. The automatic switching feature will be of value to the many patients who prefer not to manually switch programs on their CIs.

The effects of adaptive directional microphone on auditory evoked cortical P300 response and speech performance in cochlear implant users

Objective: The aim of this study was to evaluate the possible benefits of an adaptive directional microphone in noise by using auditory P300 and speech recognition scores (SRSs) in cochlear implant subjects.Design: The P300 and speech recognition scores were obtained (a) in quiet with an omnidirectional microphone (Quiet OM), (b) in noise with an omnidirectional microphone (Noise OM) and (c) in noise with an adaptive directional microphone (Noise BEAM) to compare the microphone effects.Study sample: Thirty-five cochlear implant subjects (22.87 ± 1.30 years)Results: The latencies of the P2, N2 and P3 responses as the discrimination potentials were significantly prolonged in the Noise OM condition compared with those obtained in the Quiet OM and Noise BEAM conditions (p < 0.05). The latencies of all responses in the Quiet OM and Noise BEAM conditions were similarly obtained (p > 0.05). SRSs were significantly lower in the Noise OM condition than in the Quiet OM and Noise BEAM condition (p < 0.05).Conclusions: During noise, the adaptive directional microphone system provided a discrimination ability similar to that seen in quiet settings for cochlear implant users.

The Effect of Hearing Aid Technologies on Listening in an Automobile

Communication while traveling in an automobile often is very difficult for hearing aid users. This is because the automobile/road noise level is usually high, and listeners/drivers often do not have access to visual cues. Since the talker of interest usually is not located in front of the listener/driver, conventional directional processing that places the directivity beam toward the listener's front may not be helpful and, in fact, could have a negative impact on speech recognition (when compared to omnidirectional processing). Recently, technologies have become available in commercial hearing aids that are designed to improve speech recognition and/or listening effort in noisy conditions where talkers are located behind or beside the listener. These technologies include (1) a directional microphone system that uses a backward-facing directivity pattern (Back-DIR processing), (2) a technology that transmits audio signals from the ear with the better signal-to-noise ratio (SNR) to the ear with the poorer SNR (Side-Transmission processing), and (3) a signal processing scheme that suppresses the noise at the ear with the poorer SNR (Side-Suppression processing). The purpose of the current study was to determine the effect of (1) conventional directional microphones and (2) newer signal processing schemes (Back-DIR, Side-Transmission, and Side-Suppression) on listener's speech recognition performance and preference for communication in a traveling automobile. A single-blinded, repeated-measures design was used. Twenty-five adults with bilateral symmetrical sensorineural hearing loss aged 44 through 84 yr participated in the study. The automobile/road noise and sentences of the Connected Speech Test (CST) were recorded through hearing aids in a standard van moving at a speed of 70 mph on a paved highway. The hearing aids were programmed to omnidirectional microphone, conventional adaptive directional microphone, and the three newer schemes. CST sentences were presented from the side and back of the hearing aids, which were placed on the ears of a manikin. The recorded stimuli were presented to listeners via earphones in a sound-treated booth to assess speech recognition performance and preference with each programmed condition. Compared to omnidirectional microphones, conventional adaptive directional processing had a detrimental effect on speech recognition when speech was presented from the back or side of the listener. Back-DIR and Side-Transmission processing improved speech recognition performance (relative to both omnidirectional and adaptive directional processing) when speech was from the back and side, respectively. The performance with Side-Suppression processing was better than with adaptive directional processing when speech was from the side. The participants' preferences for a given processing scheme were generally consistent with speech recognition results. The finding that performance with adaptive directional processing was poorer than with omnidirectional microphones demonstrates the importance of selecting the correct microphone technology for different listening situations. The results also suggest the feasibility of using hearing aid technologies to provide a better listening experience for hearing aid users in automobiles.

Influence of directionality and maximal power output on speech understanding with bone anchored hearing implants in single sided deafness

Bone-anchored hearing implants (BAHI) are routinely used to alleviate the effects of the acoustic head shadow in single-sided sensorineural deafness (SSD). In this study, the influence of the directional microphone setting and the maximum power output of the BAHI sound processor on speech understanding in noise in a laboratory setting were investigated. Eight adult BAHI users with SSD participated in this pilot study. Speech understanding in noise was measured using a new Slovak speech-in-noise test in two different spatial settings, either with noise coming from the front and noise from the side of the BAHI (S90N0) or vice versa (S0N90). In both spatial settings, speech understanding was measured without a BAHI, with a Baha BP100 in omnidirectional mode, with a BP100 in directional mode, with a BP110 power in omnidirectional and with a BP110 power in directional mode. In spatial setting S90N0, speech understanding in noise with either sound processor and in either directional mode was improved by 2.2-2.8dB (p=0.004-0.016). In spatial setting S0N90, speech understanding in noise was reduced by either BAHI, but was significantly better by 1.0-1.8dB, if the directional microphone system was activated (p=0.046), when compared to the omnidirectional setting. With the limited number of subjects in this study, no statistically significant differences were found between the two sound processors.

METHOD AND APPARATUS FOR PRODUCING ADAPTIVE DIRECTIONAL SIGNALS

The invention relates to adaptive directional systems, and more particularly to a method and apparatus for producing adaptive directional signals. The invention may be applied to the provision of audio frequency adaptive directional microphone systems for devices such as hearing aids and mobile telephones. The method involves constructing the adaptive directional signal (46) from a weighted sum of a first signal (42A) having an omni-directional polar pattern and a second signal (42B) having a bi-directional polar pattern, wherein the weights are calculated to give the combined signal a constant gain in a predetermined direction and to minimise the power of the combined signal. The mehtod has particular application in producing signals in digital hearing aids, the predetermined direction being in the forward direction with respect to the wearer.

Two home-brewed microphone assemblies for performing arts spaces

Two decades ago, MCH pressed into service a binaural head (rather identical to one of its principals) comprised of a human skull, paraffin wax and anatomically-correct pinnae. This has been found useful in our concert hall tuning exercises. Separately, during tuning exercises, acousticians on our team reported possible percussion echoes during amplified events at Los Angeles' new 1700-seat Valley Performing Arts Center. Anticipating a deeper forensic exercise rapidly looming, a highly directional parabolic microphone system was cobbled from ad hoc parts to quickly confirm (or not) the reports, identify problem surfaces and potential solutions, if required. The curious-appearing, but effective devices are described and their use discussed.

Hearing Aid With Directional Microphone System, And Method For Operating A Hearing Aid

The invention relates to a hearing aid with a signal processing unit and at least two microphones which can be coupled together to form directional microphone systems of a different order, where microphone signals emitted by directional microphone systems of a different order can be coupled together in a weighting dependent on the frequency of the microphone signals. The invention further relates to a method for operating a hearing aid of this type.

Automatic microphone equalization in a directional microphone system with at least three microphones

Microphone equalization is implemented in a directional microphone system of the second or a higher order with at least three omnidirectional microphones. Initially, the signal levels of the microphone signals generated by the three omnidirectional microphones are compensated. The phase is subsequently varied in one of the three microphone signals until the signal levels of the directional microphones of the first order that are formed from the three omnidirectional microphones, are also compensated.

Using a signal cancellation technique involving impulse response to assess directivity of hearing aids

The directional microphone systems of modern digital hearing aids are capable of changing their spatial directivity pattern and/or the microphone mode in response to changes in the properties of environmental sounds. These adaptive/automatic features make measurement of a hearing aid's directivity in a given test environment very difficult. Assessing the directivity of such systems requires a signal that can record the system's response while not changing the system's directivity. This paper proposes a method using a signal cancellation technique involving impulse responses to acoustically assess a hearing aid's directivity (referred to as the IR method). The impulse is presumed to be undetectable to the adaptive/automatic system because it contains little energy and a short response could be recorded before the system actually reacts. In the current study, the IR method was evaluated by testing five adaptive/automatic directional hearing aids in noise of various intensities. The results revealed that the IR method was an accurate and repeatable way to assess slow-acting directional systems in noise of varying intensities and fast-acting systems in noise of high intensities.

Speech perception with hearing aids: Effects of noise reduction and directional microphone systems on amplified signals

Our objective was to measure the variations of speech reception threshold (SRT) in noise induced by hearing aids with or without noise reduction (NR) and directional microphone systems (DM). Data were collected from 10 normal hearing volunteers wearing bilateral hearing aids and tested in a sound field of speech and noise. SRT was measured in function of: 1) speech source azimuth (0°,90°,180°); 2) background noise (monophonic vs. quadraphonic); 3) amplification (unaided vs. linearly aided); 4) amplification mode (linear, NR, DM, NR + DM). Compared using a hearing aid linear setting, NR does not improve the SRT in monophonic noise, while it improves the SRT by 2–3dB in quadraphonic noise with frontal and lateral speech. DM in monophonic noise improves frontal SRT (1dB) and worsens lateral and posterior SRT, while in quadraphonic noise frontal SRT is further advantaged and the DM negative effect disappears. With both devices activated a stronger positive effect is evident for frontal SRT in both noise field...

Speech-in-noise enhancement and sound localization with improved binaural hearing instruments

Multi-microphone noise reduction schemes have become standard in commercial hearing aids and cochlear implants. Recent studies with bilateral hearing aids have shown that common adaptive directional microphone systems tend to distort localization cues, leading to inappropriate and reduced spatial awareness for bilateral hearing aid users. Here we show that binaural multi-microphone signal processing based on multi-channel Wiener filter (MWF) are capable of combining noise reduction with the preservation of directional hearing. Physical simulations and perceptual results from 10 listeners have been studied for different noise source scenarios, in different reverberant conditions, and for a number of signal processing schemes using up to 4 microphone inputs (2 each side). An overview is given of the localization performance and the speech reception benefits in these different listening conditions for the different noise reduction strategies. An adaptive directional microphone system (ADM) is used as a reference system. Signal processing based on MWF does, unlike ADM, provides a combination of noise reduction and preservation of spatial awareness. Moreover, in some conditions it even offers an improved spatial release from masking. The MWF outperforms the ADM in terms of localization and noise reduction if signals are not arriving from the most forward field of view.

Hearing aid device, comprising a directional microphone system and a method for operating a hearing aid device

The invention relates to a hearing aid device, comprising a signal processing unit (14) and at least two microphones (1, 2, 3) which can be coupled together to form directional microphone systems of a different order, whereby microphone signals (11, 12, 13) transmitted by directional microphone systems of a different order can be coupled together according to the weighting of the frequency of the microphone signals. The invention also relates to a method for operating a hearing aid device of this type.

Evaluation of the Benefit for Cochlear Implantees of Two Assistive Directional Microphone Systems in an Artificial Diffuse Noise Situation

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. 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. 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. 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.

Predictive Measures of Directional Benefit Part 1: Estimating the Directivity Index on a Manikin

In this investigation, a method for computing a directivity index (DI) on a manikin for directional microphones in hearing aids was proposed and evaluated comparatively to other conventional methods. Test devices included first- and second-order directional microphones. Signal presentation, implemented in an anechoic chamber, involved a single noise source rotated completely around the directional microphone in a hearing aid, in free field and on a manikin, at a defined radius. The area covered was equivalent to the approximate surface area of a sphere. It was anticipated that an equal angular resolution of 10 degrees (elevation and azimuth) would effectively estimate the DI of first-, second-, and higher-order directional microphone systems located in a hearing aid on a manikin. A total of 450 spatially varied presentation points were analyzed, each weighted in reference to direction of arrival on the directional microphone. Empiric differences between the DI derived from the 3D-DI method proposed in this investigation and the conventionally derived 2D-DI method DI on a manikin were as large as 3.8 dB in the higher frequencies, depending on the device under test. The magnitude of these differences was dependent on the device under test microphone location. The further the microphone was placed into the ear of the manikin, the larger the empiric differences.

Directional-microphone and method for signal processing in same

Provided is a directional-microphone system, as well as a method for signal processing in such a directional-microphone system, wherein a particularly controllable second-order directional-microphone pattern is ensured while the number of figure-of-eight microphones required to generate such pattern is minimized.

Post-processing scheme for adaptive directional microphone system with noise/interference suppression

The present invention provides an adaptive directional microphone system for enhancing an acoustic signal from a second direction and for reducing an acoustic signal from at least a first direction different from the second direction, the system comprising: an omni-directional microphone and a directional microphone being arranged in a closely acoustically-coupled way; an adaptive filtering circuit system for generating a first error e1(n) corresponding to an acoustic signal in which the acoustic signal from the first direction is reduced; and a post-processing filter system for producing a second error signal e2(n) corresponding to an acoustic signal in which the acoustic signal from the second direction is enhanced as compared to the acoustic signal related to the first error signal e1(n).

Comparative Performance of an Adaptive Directional Microphone System and a Multichannel Noise Reduction System

The amplification outcomes of two hearing aid prescriptions, NAL-NL1 and Digital Perception Processing (DPP), of nine moderate to moderately severe hearing-impaired adults were compared in the same digital hearing instrument. NAL-NL1 aims at optimizing speech intelligibility while amplifying the speech signal to a normal overall loudness level (Dillon, 1999). DPP focuses on restoring loudness based on normal and impaired cochlear excitation models (Launer and Moore, 2003). In this comparison, DPP resulted in better sentence recognition performance than the NAL-NL1 algorithm in the signal-front/noise-side condition, and the two prescriptions gave similar performance in the signal-front/noise-front condition. Subjective evaluations by the participants using the Abbreviated Profile for Hearing Aid Benefit and sound quality comparisons did not give conclusive results between the two prescriptions. With each hearing aid prescription, the ability of the hearing aid circuitry to reduce the effects of noise was evaluated by a sentence-in-noise test in three conditions: (1) adaptive directional microphone (DAZ), (2) multichannel noise reduction system (FNC), and (3) a combination of FNC and DAZ (FNC + DAZ). In the signal-front/noise-side condition, DAZ and FNC + DAZ gave better performance than FNC in nearly all participants, whereas in the signal-front and noise-front evaluation, the conditions revealed no significant differences.

Microphone array having a second order directional pattern

A directional microphone system is disclosed, which comprises circuitry for low pass filtering a first order signal, and circuitry for high pass filtering a second order signal. The system further comprises circuitry for summing the low pass filtered first order signal and the high pass filtered second order signal. A method of determining whether a plurality of microphones have sufficiently matched frequency response characteristics to be used in a multi-order directional microphone array is also disclosed. For a microphone array having at least three microphones, wherein one of the microphones is disposed between the other of the microphones, a method of determining the arrangement of the microphones in the array is also disclosed.

Method and apparatus for suppressing an acoustic interference signal in an incoming audio signal

In order to suppress at least one interference signal in an incoming audio signal using a directional microphone system having at least two microphones, that directional microphone signal which has the lowest interference signal component is selected from two or more directional microphone signals that have been produced by weighted combination from the signals of the microphones, with the weighting in each case determining a direction-dependent sensitivity. If a sensitivity distribution has a minimum in the direction of the interference signal source, then a low signal energy is detected, which characterizes a lower interference signal component.

Speech Recognition and Comfort Using Hearing Instruments with Adaptive Directional Characteristics in Asymmetric Listening Conditions

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). 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. 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. 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.