EP1489883A2 - Adaption automatique des microphones - Google Patents

Adaption automatique des microphones Download PDF

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Publication number
EP1489883A2
EP1489883A2 EP04010368A EP04010368A EP1489883A2 EP 1489883 A2 EP1489883 A2 EP 1489883A2 EP 04010368 A EP04010368 A EP 04010368A EP 04010368 A EP04010368 A EP 04010368A EP 1489883 A2 EP1489883 A2 EP 1489883A2
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Prior art keywords
matching
acoustical
converters
signal
unit
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German (de)
English (en)
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EP1489883A3 (fr
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Hans-Ueli Roeck
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Sonova Holding AG
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Phonak AG
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
    • H04R25/40—Arrangements for obtaining a desired directivity characteristic
    • H04R25/407—Circuits for combining signals of a plurality of transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R29/00—Monitoring arrangements; Testing arrangements
    • H04R29/004—Monitoring arrangements; Testing arrangements for microphones
    • H04R29/005—Microphone arrays
    • H04R29/006—Microphone matching

Definitions

  • the present invention is directed on a method for matching at least two acoustical to electrical converters which generate, respectively, electrical output signals. Signals which depend on the electrical output signals of the converters are computed to result in a result signal.
  • the transfer characteristic between an acoustical signal impinging upon the at least two converters and the result signal is dependent on direction of arrival - DOA - of the acoustical signal upon the at least two converters.
  • Beamformers Acoustical pickup arrangements which have a transfer characteristic between acoustical input and electrical output, the amplification thereof being dependent on the DOA of acoustical signals on the acoustical inputs of such devices are called “beamformers" and are widely used as e.g. for hearing devices, be it outside-the-ear hearing devices or in-the-ear hearing devices, be it for such hearing devices to improve and facilitate normal hearing or be it for such hearing devices for therapeutic appliances, i.e. to improve hearing capability of hearing impaired persons. Further, beamformers may also be applied for hearing protection devices, whereat the main target is to protect an individual from excessive acoustical loads.
  • the addressed transfer characteristic when represented in polar coordinates, is of one or more than one lobe and has accordingly one or more minima, called “Nulls”, at specific values of DOA.
  • Beamformers may be conceived just by acoustical to electrical converters which per se have a beamforming characteristic.
  • the present invention deals with other cases where at least two spaced apart acoustical to electrical converters are used, signals dependent on their electrical output signals being computed to generate a result signal. It is by such computing that the desired beam characteristic is generated, between the acoustical input signals and the result signal. Often the at least two converters have omni-directional characteristics and it is only by the addressed computing that beamforming is achieved. Nevertheless, converters which have intrinsic beamforming ability may also be used but the desired transfer characteristic is conceived finally by the addressed computing.
  • a beam characteristic is realized by computing the electrical output signals of at least two acoustical to electrical converters or from more than two of such converters, whether a desired beam characteristic is accurately achieved depends from how accurately the involved converters provide for assumed predetermined transfer characteristics between their acoustical inputs and their electrical outputs.
  • the desired beam characteristic is designed based on the assumption of identical transfer characteristics of the converters involved. Obviously, in such case the converters are made to be matched if the real transfer characteristics between acoustical input signals and respective possibly mutually adjusted electrical output signals are identical.
  • the process of matching the converters means mutually adjusting their electrical output signals so that the respective real transfer characteristics differ less than without such mutual adjusting and become, due to the mutual adjustment, in the ideal case, identical.
  • omni-directional converters which are mutually spaced by a predetermined distance, mutually delaying the output signals of the converters and subtracting the mutually delayed electrical signals which results in an overall beam characteristic which, with omni-directional converters, is of cardoid, hypercardoid, bidirectional or some other shape.
  • Directivity of the resulting beam characteristic depends on one hand from the mutual distance of the converters, on the other hand from the possibly adjustable, thereby often automatically adjustable mutual delay, and from the accuracy with which the converters are matched.
  • the electrical output signals of two microphone converters are fed via controlled matching amplifier units to a computing unit.
  • the output signal of the computing unit has, with respect to acoustical input signals, a beam characteristic.
  • the output signal powers resp. magnitudes of the matching amplifier units are averaged and the averaged signals compared by difference forming.
  • the comparing result signal is fed to an analyzing and controller unit which controls the matching amplifier units. Thereby, the matching is performed in a negative feedback structure up to the comparing result of the two averaged signals vanishes. If this occurs the two input converters are considered to have been matched.
  • the output signals of two microphones are computed.
  • a result signal establishes with respect to the acoustical input signals a beamforming transfer characteristic.
  • Each of the electrical output signals of the microphones is fed to a respective minimum estimation unit, the outputs thereof to a division unit.
  • the result of the division controls a matching unit, namely a multiplying unit.
  • the US 2001/0038699 teaches to disable the directivity of the transfer characteristic, i.e. the beam characteristic of a two-microphone-based beamformer whenever "only noise" situation is recognized, thereby disabling one of the two microphones to reduce overall noise and maintaining only one microphone operative.
  • the present invention departs from the following recognitions:
  • a beamforming device or beamformer which is based on at least two acoustical to electrical input converters, signals dependent on the output signals of these converters being computed, e.g. by delay-and-subtract operation, is applied in non-free field acoustical surrounding, such non-free field surrounding presents per se acoustical signal attenuation which varies as a function of spatial angle at which the acoustical source is seen from the acoustical input of the device.
  • Such non-free field acoustical transfer characteristic called "in-situ" characteristic, which varies with DOA is often important to be maintained as an informative entity.
  • the head-related transfer function HRTF provides for an acoustic in-situ transfer characteristic between an acoustical source and the at least two converters, which differs from individual to individual and which varies significantly with varying DOA. If a sound source is thought to travel on a circular locus around an individual's head, the in-situ transfer characteristic between the acoustical source and individual's ear may vary by more than 10 dB as a function of DOA. The individual exploits such DOA dependency for localizing acoustical sources. Thus, such characteristic should not be spoiled by converter matching.
  • the method for matching at least two acoustical to electrical converters comprises matching the at least two converters for acoustical signals in dependency of an impinging direction of arrival within a range of direction of arrival upon said converters, said range being determined before performing said matching.
  • the range of DOA of acoustical signals for which matching is performed is selected so that the in-situ transfer characteristic is known and in advance, as an example, is known to be neglectable.
  • Techniques to evaluate the DOA of acoustical signals impinging on at least two acoustical to electrical converters of a beamforming device are known.
  • DOA evaluation is also strongly linked to time delay estimation for which numerous methods like cross-correlation, MUSIC, etc. are well known in the art. M. Brandstein “Microphone arrays", Springer, ISBN 3-540-41953-5 gives a nice overview over such methods. US 20010031053 shows another method for DOA estimation which is leaned on processes found in nature.
  • a range of DOA which is most suited to be exploited according to the present invention is where the desired transfer characteristic has minimum gain, i.e. around a "Null". This because signals impinging from the respective direction shall - according to the desired "Null" - be cancelled. Therefore, a realization form of the method according to the present invention, whereat the transfer characteristic has a minimum for a value of DOA, comprises matching the at least two converters for acoustical signals which impinge within the range determined before matching which includes such value of DOA.
  • Beamformers are further known which make use of at least two acoustical/electrical converters, signals dependent from their output signals being computed by a first computing and at least a second computing.
  • the at least two computings result in respective first and second result signals.
  • a first transfer characteristic between an acoustical signal impinging on the at least two converters and the first result signal and which is dependent on DOA is differently dependent on DOA than a second transfer characteristic between the acoustical input signal and the second result signal.
  • Such beamforming devices are e.g. realized by the so-called Griffith Jim-based beamformers as exemplified e.g. in the US 5 473 701 to AT&T.
  • matching is performed independently for the addressed first and at least one second computing, for acoustical signals which respectively impinge from ranges of DOA determined before matching upon the at least two converters. These ranges may be selected to be equal or to be different.
  • matching is performed selectively in frequency bands determined before matching, whereby in a further embodiment of the invention analog to digital and time-domain to frequency-domain conversion is performed between the electrical output of the at least two converters and computing.
  • a method for suppressing feedback between an acoustical output of an electrical/acoustical output converter arrangement and an acoustical input of an acoustical/electrical input converter arrangement of a hearing device is addressed.
  • acoustical signals impinging on an input converter arrangement are converted into a first electrical signal by a controllably variable transfer characteristic which is dependent on the angle (DOA) at which the acoustical signals impinge on the input converter arrangement.
  • DOA angle
  • the acoustical/electrical input converter arrangement as addressed in the Attachment A wherein acoustical signals impinging on the input converter arrangement are converted into a first electrical signal by a controllably variable transfer characteristic which is dependent on the angle at which the acoustical signals impinge on the input converter arrangement, accords in the present description to the at least two acoustical to electrical converters, computing and generating the result signal.
  • the result signal is operationally connected via a processing unit to an electrical/acoustical output converter arrangement.
  • the teaching according to the Attachment A addresses a method for suppressing feedback between the output of such electrical/acoustical output converter arrangement and the input of the at least two converters as addressed in the present description.
  • the at least two input converters are to be matched during operation, i.e. automatically, whereby in fact the real transfer characteristic is adjusted.
  • Attachment A of an adaptive beamformer unit This accords with the definition in Attachment A of an adaptive beamformer unit.
  • the result signal is operationally connected to an output electrical/acoustical converter as of a hearing device and there is provided, as described in the Attachment A in details, a feedback compensator, the input of which being operationally connected to the input of the output converter arrangement, the output of which being fed back, the complex task of estimating the feedback signal to be suppressed by the feedback compensator e.g. by correlation leads to the fact that the feedback compensation process has a relatively long adaptation time constant to adapt from one feedback situation to be suppressed to another by appropriately varying the loop gain of the feedback loop. As described in the Attachment A such an adaptation time constant is customarily in the range of hundreds of msec.
  • the matching process which is addressed in the present application defines as well for an adaptation time constant of the adaptive beamformer.
  • the adaptation time constant for "matching adaptation” is significantly shorter than the adaptation time constant as realized by the feedback compensator. Therefore, and if according to one aspect of the present invention a feedback compensator is provided as explained in detail in the addressed Attachment A , the same problems arise as also explained in the addressed Attachment A , namely the problem that the feedback compensator may not follow quick changes of feedback situations which are caused by the short adaptation time constants of matching adaptation.
  • the addressed result signal is operationally connected to an electric input of an electrical to acoustical converter and which comprises feeding back an electric feedback compensating signal which is dependent on an input signal to the electrical to acoustical converter and superimposing the fed-back signal to the result signal, wherein further the adaptation rate of matching according to the present invention is controlled in dependency of the loop gain along the feedback signal path.
  • the present invention under a second aspect by providing for a method for matching at least two acoustical to electrical converters, signals dependent on the electrical output signals of the converters being computed to result in a result signal and wherein the transfer characteristic between an acoustical signal impinging upon the at least two converters and the result signal is dependent on direction of arrival of the acoustical signal on the at least two converters, wherein matching of the converters is performed with a matching time constant ⁇ , for which there is valid: 0 ⁇ ⁇ ⁇ 5 sec.
  • a beamforming device comprises at least two acoustical to electrical converters and at least one computing unit, the electrical output of the converters being operationally connected via a matching unit to inputs of the at least one computing unit. Thereby, the output of the beamforming device is operationally connected to the output of the at least one computing unit.
  • the computing unit further generates a signal which is indicative of DOA of an acoustical signal which impinges on the at least two converters.
  • the device further comprises a matching control unit which generates a matching control signal which is operationally connected to a control input of the matching unit.
  • the signal which is indicative of DOA is further operationally connected to a control input of the matching control unit, which further has at least two inputs which are operationally connected to respective outputs of the at least two converters, in feedback structure downstream the matching unit, in feed-forwards structure upstream the matching unit.
  • a beamforming device comprising at least two acoustical to electrical converters and at least one computing unit, the electrical output of said converter being operationally connected via a matching unit to inputs of said at least one computing unit, the output of said beamforming device being operationally connected to the output of said at least one computing unit, a matching control unit generating a matching control signal operationally connected to a control input of the matching unit, said matching unit comprising at least two inputs operationally connected to the outputs of said at least two converters upstream or downstream said matching unit and wherein said matching control unit generates the matching control signal so as to match the at least two converters with a matching time constant ⁇ for which there is valid: 0 ⁇ ⁇ ⁇ 5 sec.
  • the matching time constant ⁇ is: 0 ⁇ ⁇ ⁇ 1 sec.
  • a number of acoustical to electrical converters as shown two such converters 1a and 1b, have electrical outputs A 1a , A 1b which are operationally connected to inputs E 3a and E 3b of a matching unit 3.
  • signals which are applied to the inputs E 3a and E 3b are adjusted with respect to at least one of their characteristics, e.g. with respect to frequency response, amplitude and/or phase response or other characteristic features.
  • Respective adjusting members are provided in unit 3, e.g. as shown in channel a or b or in both channels a and b.
  • the outputs A 3a and A 3b are operationally connected to inputs E 7a and E 7b of a computing unit 7 which has an output A 7 and an output A DOA .
  • beamforming is computed from the signals applied to the inputs E 7a , E 7b e.g. by delay-and-subtract computing.
  • the result of beamforming is fed to output A 7 as a result signal of the beamforming operation.
  • the direction of arrival DOA of acoustical signals impinging upon the converters 1a and 1b is computed from the signals applied to E 7a , E 7b resulting in an output signal fed to output A DOA of computing unit 7 which is indicative of DOA of the addressed acoustical signals.
  • DOA performing monitoring of the DOA is e.g. realized as described in the WO 00/33634 which was already mentioned above or as taught by the following publications: M. Brandstein "Microphone arrays", Springer, ISBN 3-540-41953 or US 2001003053.
  • a DOA of computing unit 7 there is generated a signal which is indicative of the direction of arrival DOA.
  • This signal is operationally connected to a comparator unit 9, where it is checked, whether the instantaneously evaluated DOA signal is within a range ⁇ DOA around a value DOA S . Determination, whether the actual DOA signal is within this range DOA S ⁇ DOA is performed by comparing the DOA indicative signal from the output A DOA with a signal range which is preset at input E 9C of unit 9. Whenever it is detected in unit 9 that the prevailing DOA signal is within the predetermined range, unit 9 generates at an output A 9 a control signal which is operationally connected to a control input E 11C of a matching control unit 11.
  • the matching control unit 11 has two further inputs E 11a and E 11b which are operationally connected to the electric output A 1a and A 1b of the respective converters.
  • the signals applied to the input E 11a and E 11b are compared as shown in block 11 e.g. by difference forming and an output signal is generated at output A 11 of matching control unit 11, which is dependent on the result of such comparison.
  • the signal applied to control input E 11c enables the comparison result dependent signal to become effective via output A 11 on adjustment control input E 3c of matching unit 3, controlling the adjustant members provided in matching unit 3.
  • the at least two signals which are fed to the computing unit 7 at E 7a and E 7b are adjusted to become less different.
  • fig. 1 shows a feed forwards structure
  • same technique may be realized in a feed-back structure (not shown) by connecting the inputs E 11a and E 11b not to the outputs of the converters 1a and 1b upstream unit 3, but instead to the outputs A 3a and A 3b downstream matching unit 3.
  • Representation (a) shows as an example the transfer characteristic in polar representation of an omnidirectional converter as of converter 1a of fig. 1.
  • Representation (b) shows such transfer characteristic again as an example of the second converter as of 1b of fig. 1.
  • beamforming within computing unit 7 leads e.g. to the cardoid transfer characteristic as shown in representation (c) which is e.g. realized by the delay-and-subtract method.
  • the instantaneously prevailing DOA is estimated as shown in representation (d) to be ⁇ .
  • DOA S 0, at which a "Null" of the desired transfer characteristic as of representation (c) is expected.
  • matching of the converters via matching control unit 11 it is possible to softly weigh the effect of the comparing result computed in matching control unit 11 upon the adjusting members in matching 3 e.g. as a function of deviation between estimated DOA and DOA S as determined before performing matching. Such weighing may e.g. be realized so that such effect becomes the weaker resp. the matching frozen the more that the estimated DOA deviates from DOA S .
  • fig. 3 a further embodiment of a device according to the present invention operating according to the method of the invention is shown.
  • the same reference numbers are used in fig. 3 as in fig. 1 for elements which have already been described in context with fig. 1.
  • the unit comprising the converters 1a, 1b, matching unit 3, computing unit 7, matching control unit 11, provides for an adaptive beamformer unit 20 A , whereby being adapted by adjusting the overall transfer function by converter matching.
  • the output A 7 of the adaptive beamformer 20 A is operationally connected to a superimposing unit 20 AP .
  • the output of the superimposing unit 20 AP is input to processing unit 14 AP , the output thereof being operationally connected to the input of an electrical to acoustical converter arrangement 16 AP .
  • the combined structure of beamformer 20A, processing unit 14 AP and electrical to acoustical converter arrangement 16 AP is a structure typical e.g. in hearing device applications.
  • a compensator unit 18 AP has an input operationally connected to the input of the converter arrangement 16 AP and an output operationally connected to one input of the superimposing unit 20 AP .
  • the negative feedback loop with compensator unit 18 AP provides for compensation of acoustical feedback from the acoustical output of converter arrangement 16 AP to the acoustical input of the converters 1a, 1b.
  • the compensator unit 18 AP has an output A GAP , whereat a signal is generated which is indicative of the loop gain of the negative feedback loop.
  • This loop gain may e.g. be estimated by multiplying the linear gains along the loop which primarily consists of the compensator unit 18 and of processing unit 14 AP or by adding these gains in dB.
  • the loop gain indicative signal at output A GAP is fed to a control input C 12RAP of the adaptive beamformer 20 A and therein to a control input of matching control unit 11.
  • the matching adaptation rate at matching unit 3 and via matching control unit 11 is slowed down at least down to the adaptation rate of compensator unit 18 AP in dependency of the prevailing feedback effect and thus of the loop gain of compensator unit 18 AP .
  • fig. 4 a further embodiment of the present invention is shown. Again, reference numbers which were already used in context with fig. 1 or 3 are used for elements which have already been described. According to the embodiment of fig. 4 the outputs A 1a and A 1b of the at least two converters 1a and 1b are operationally connected to a first matching unit 3 I and to a second matching unit 3 II .
  • the outputs of the two matching units 3 I and 3 II are operationally connected to respective computing units 7 I and 7 II .
  • a first result signal At the output A 7I there appears a first result signal.
  • a first transfer characteristic which is differently dependent on DOA than a second transfer characteristic which prevails between the acoustical input signal upon converters 1a and 1b and a signal generated at output A 7II of the second computing unit 7 II .
  • Matching of the converters with respect to first beamformer I is performed via unit 9 I , matching control unit 11 I in analogy to the one beamformer technique of fig. 1. Further in complete analogy matching of the converters 1a and 1b with respect to the second beamformer II is performed via unit 9 II , matching control unit 11 II .
  • a feedback structure is shown in that the outputs of the respective matching units 3 I and 3 II are fed for comparison purposes to the matching control units 11 I and 11 II .
  • signal processing may be performed in analog or digital or hybrid technique.
  • Converter matching selectively in frequency bands which are determined before performing matching is simplified by signal processing in the frequency domain.
  • converter matching is only then performed when an acoustical signal impinges on the input converters within a range of DOA and this range may be selected in an optimum direction with an eye on in-situ situation, it is achieved that automatic in-situ converter matching is feasible without affecting the effects of the in-situ acoustic situation.
  • time constant ⁇ may be even selected to be: 0 ⁇ ⁇ ⁇ 1 sec. or even to be 0 ⁇ ⁇ ⁇ 100 msec.
  • a beamformer technique is addressed under a second aspect which makes use of at least two acoustical to electrical converters and where converter matching is performed with matching time constants ⁇ for which the addressed ranges are valid.
  • the present invention deals with a method for suppressing feedback between an acoustical output of an electrical/acoustical output converter arrangement and an acoustical input of a acoustical/electrical input converter arrangement of a hearing device, wherein acoustical signals impinging on the input converter arrangement are converted into a first electrical signal, by a controllably variable transfer characteristic and which is dependent on the angle at which said acoustical signals impinge on the input converter arrangement.
  • the first electrical signal is processed and a resulting signal is applied to the output converter.
  • an electrical feedback-compensating signal generated in dependency of the result signal which is applied via a feedback signal path upstream the processing.
  • a unit to which the output of the input converter arrangement is input and which provides a signal transfer characteristic to its output which has an amplification dependent on spatial angle at which acoustical signals impinge on the acoustic input of the input converter arrangement is called a beamformer unit.
  • the transfer characteristic in polar representation is called the beam.
  • An adaptive beamformer unit is a beamformer unit, the beam generated therefrom being controllably variable.
  • the feedback-compensation process Due to the complex task of estimating the feedback-signal to be suppressed e.g. by correlation at the feedback-compensator, the feedback-compensation process has a relatively long adaptation time constant to adapt from one feedback situation to be suppressed to another by appropriately varying its gain.
  • Such an adaptation time constant is customarily in the range of hundreds of milliseconds.
  • a behind-the-ear hearing device 3 with an input converter arrangement 5 applied at the pinna 1 of an individual experiences feedback to be suppressed from a distinct direction as shown at d1.
  • An in-the-ear hearing device 7 according to Fig. 2 which has, as an example, a vent 9 and two acoustical ports 11 to the input converter arrangement, experiences feedback signals to be suppressed from the distinct directions d2.
  • a further approach for suppressing feedback is to install high signal attenuation between the input and the output converter of the device for signals which impinge on the input converter under such distinct spatial angles. This accords with applying a beamformer technique generating a beam having zero or minimum amplification at such angles.
  • Hearing devices which have adaptive beamformer ability are known e.g. from the WO 00/33634.
  • feedback compensation techniques as e.g. known from the EP 0 656 737 with adaptive beamformer technique as e.g. known from the WO 00/33634 and thereby to place minimum amplification of the beam at those angles which are specific for feedback signals to be suppressed impinging on the input converter. This especially because these angles are clearly different from the target direction range within which maximum amplification of the beam is to be variably set.
  • the adaptation time constant of an adaptive beamformer unit is considerably smaller, in the range of single to few dozen milliseconds, than the adaption time constant of a feedback-compensator which is, as mentioned above, in the range of hundreds of milliseconds.
  • a beamformer unit is provided, the input thereof being operationally connected to two mutually distant microphones of an input converter arrangement.
  • two feedback compensators are provided with inputs operationally connected to the input of the output converter arrangement. The respective output signals are superimposed to the respective output signals of the two microphones.
  • a third approach is proposed in M. Brandenstein et al. as mentioned and in W. Herbold et al. "Computationally efficient frequency domain combination of acoustic echo cancellation and robust adaptive beamforming".
  • a generalised side lobe cancelling technique for the beamformer is used whereat only a not-adaptive beamformer is placed upstream the compensation feedback path, thus eliminating the adaptation time problem as well as double computational load. Nevertheless, by this approach placing minimum amplification of the beam in the direction of feedback signal arrival may not be realised.
  • a method for suppressing feedback between an acoustical output of an electrical/acoustical output converter arrangement and an acoustical input of an acoustical/electrical input converter arrangement of a hearing device wherein acoustical signals impinging on the input converter arrangement are converted into a first electric signal by a controllably variable transfer characteristic which is dependent on the angle at which said acoustical signals impinge on said input converter arrangement.
  • the first electric signal is processed and a resulting signal is applied to the output converter arrangement.
  • the feedback to be suppressed is compensated by a feedback compensating signal which is generated in dependency of the resulting signal and is fed back by a feedback signal path to a location along the signal path upstream the processing.
  • the feedback-compensating signal is fed back to the first electric signal - thus downstream the beamformer - and the adaptation rate of converting to variations of the transfer characteristic - and thus of beamforming - is controlled in dependency of gain along the compensator feedback signal path.
  • the adaptation rate of the adaptive beamformer unit the speed with which the beamformer unit reacts on an adaptation command to change beamforming operation as e.g. changing target enhancement or noise suppression direction.
  • the adaptation rate accords with an adaptation time constant to change from one beamforming polar pattern to another.
  • the compensator thereby estimates the prevailing situation of feedback to be suppressed e.g. by a correlation technique between the signal applied to the output converter arrangement and the signal received from the input converter arrangement as e.g. described in the EP 0 656 737.
  • the adaptation rate of the compensator accords with an adaptation time constant too. Whenever the loop gain along the compensating feedback signal path increases, this is caused by an increasing amount of feedback to be suppressed and thus to be compensated.
  • the adaptation rate of the beamformer unit is to be slowed down so that the compensator feedback signal may model the response of the beamformer unit too.
  • the adaptation rate of converting i.e. of beamforming is slowed down with increasing loop gain along the feedback signal path.
  • amplification of the transfer characteristic representing beamforming is minimized at one or more than one specific angles which accord to angles at which the feedback to be suppressed predominantly impinges on the input converter arrangement.
  • the compensator may still model the beamformer without losing the established minimum or minima in the direction of the said specific angles.
  • the feedback to be suppressed is a narrow band acoustical signal, thus in a further improvement of the method according to the present invention, it is not necessary - so as to deal with a feedback to be suppressed - to control and especially to slow down the adaptation rate of beamforming conversion in the entire frequency range beamforming is effective at, but it suffices to controllably adapt the adaptation rate of the beamforming conversion at frequencies which are significant for the feedback signal to be suppressed. Therefore, in a further preferred embodiment of the present invention, controlling of the adaptation rate of the beamforming conversion is performed frequency selectively.
  • the principal according to the present invention may be applied at hearing devices where signal processing is performed in analog technique, it is preferred to perform the method in devices where signal processing is performed digitally.
  • at least signal processing in the beamforming conversion as well as along the feedback compensation path is performed in frequency domain, whereby time domain to frequency domain conversion may be realised in a known manner, be it by FFT, DCT, wavelet transform or other suitable transforms.
  • the respective reconversion for the signal applied to the output converter arrangement is performed with the respective inverse processes.
  • the adaptation rate is controlled at selected frequencies in dependency of the compensator gain at these selected frequencies.
  • beamforming is only effective with respect to the feedback to be suppressed at specific frequencies or at a specific frequency band on the one hand the control of the adaptation rate of beamforming is in fact only to be performed at these specific frequencies or for the addressed frequency band. Further, selecting minimum amplification at the specific feedback impingement angles must be provided at the beamformer only for the specific frequencies or for the frequency band of the feedback to be suppressed too. Thus, this leads to the recognition that in fact beamforming may be subdivided in beamforming for frequencies which are not significant for the feedback to be suppressed and beamforming for frequencies or the frequency band which is specific for the feedback signal to be suppressed.
  • beamforming in the addressed specific frequencies may be performed and its adaptation rate controlled independently from tailoring beamforming at frequencies which are not specific for the feedback signal to be suppressed.
  • This beamforming may be performed at adaption rates which are independent from feedback compensation and thus faster and which generates a beam which is not dealing with the specific impinging angles of the feedback signal to be suppressed.
  • performing controlling of beamforming is done selectively at frequencies which are significant for the feedback to be suppressed.
  • Further preferred minimalising the amplification of the beamforming transfer characteristic is only done at specific angles in a frequency selection manner.
  • two independent beamforming actions are superimposed, a first dealing with the generically desired beamforming behaviour, a second dealing with feedback suppression as concerns frequencies and as concerns beamshaping. It becomes possible e.g. to switch off first beamforming, thereby maintaining the second and thereby preventing acoustical feedback to become effective.
  • the method according to the present invention may be applied to behind-the-ear hearing devices or to in-the-ear hearing devices, monaural or binaural systems, and further may be applied to such devices which are conceived as ear protection devices i.e. protecting the human ear from excess acoustical load, or to hearing improvement devices be it just to improve or facilitate hearing by an individual, or in the sense of a hearing aid, to improve hearing of a hearing impaired individual.
  • ear protection devices i.e. protecting the human ear from excess acoustical load
  • hearing improvement devices be it just to improve or facilitate hearing by an individual, or in the sense of a hearing aid, to improve hearing of a hearing impaired individual.
  • a hearing device which comprises:
  • Fig. 3 there is schematically shown, by means of a signal flow-/functional block-diagram a device according to the present invention, whereat the method according to the invention is realised.
  • the device comprises an input acoustical/electrical converter arrangement 10, which cooperate with a beamformer unit 12.
  • the conversion characteristics of the input converter arrangement 10 together with signal processing in beamformer unit 12 provides a beamformer characteristic between acoustical input E 10 to input converter arrangement 10 and electrical output A 12 of the beamformer unit 12.
  • the beamformer unit 12 has an adaptation control input C 12A and ⁇ adaptation rate control input C 12R .
  • the transfer characteristic between E 10 and A 12 has an amplification which is dependent on the angle ⁇ at which acoustical signals impinge on the acoustical port of input converter 10.
  • ⁇ the angle at which acoustical signals impinge on the acoustical port of input converter 10.
  • the transfer characteristic in polar representation the beam B, may be varied with respect to its characteristics as e.g. with respect to target direction, maximum amplification etc. as shown in dotted line within block 12.
  • Variation of the beam characteristic B is controlled by control input C 12A which latter is, as shown in dotted line, normally connected to a processing unit 14 for adapting the beam characteristic B e.g. to prevailing acoustical situations automatically or program controlled or by an individual wearing the hearing device.
  • Beamforming units which may be adapted are known. One example thereof is described in the WO 00/33634.
  • Variation of the beam characteristic B may also be caused at the beamformer itself, i.e. by beamformer internal reasons.
  • the input C 12A and control signals applied thereto are merely a schematic representation of beam characteristic variation ability or occurrence.
  • the electrical output of beamforming unit 12, A 12 is operationally connected to an input E 14 , of the signal processing 14 unit whereat input signals are processed and output at an output A 14 operationally connected to an electric input E 16 of an output electrical to acoustical converter arrangement 16 so as to provide desired ear protections or hearing improvement to the individual carrying such device.
  • ear protecting ability the ability of reducing or even cancelling acoustical signals which impinge on the input converter arrangement 10, so as to protect individual's hearing or even provide the individual with silent perception in non-vanishing acoustical surroundings.
  • hearing improvement we understand the improvement of individual's hearing in an acoustical surrounding, be it for customary applications of normal hearing individual or be it in the sense of hearing aid to improve individual's impaired hearing.
  • acoustical feedback AFB between the acoustical output of the output converter 16 and acoustical input E 10 of the input converter arrangement 10.
  • a feedback compensator 18 whereat the prevailed acoustical feedback AFB, which is to be suppressed, is estimated e.g. with a correlation technique, correlating the signal applied to output converter 16 with a signal dependent on the output of input converter 10 as shown in dashed line at A.
  • the gain G of compensator 18 is estimated so a to compensate for the AFB by negative feedback.
  • compensator unit 18 By means of compensator unit 18, a signal as predicted is fed back to the input of processor unit 14 downstream the output of beamformer unit 12 so as to compensate for the feedback AFB.
  • the compensator unit 18 has an input E18 which is operationally connected to the output A 14 of the processing unit 14 and has an output A 18 which is superimposed to the output E 12 of beamformer unit 12, the result of such superimposing being input to input E 14 of processing unit 14.
  • the compensator unit 18 which computes estimation of the acoustical feedback to be suppressed, has an adaptation rate in the range of several hundred ms and is thus considerably slower than the adaptation rate of beamforer unit 12.
  • the compensator 18 will not be able to accurately rapidly deal with the varied situation with respect to acoustical feedback AFB.
  • the loop gain may at be least estimated e.g. by multiplying the linear gains along the loop, primarily consisting of the compensator 18 and the processing unit 14 in Fig. 3 or by adding these gains in dB.
  • adaptation rate control of beamformer unit 12 is performed in dependency of the loop gain along the feedback loop with compensator unit 18.
  • the rate control input C 12R to beamforming unit 12 is operationally connected to a loop gain output A G of unit 18.
  • the direction with which acoustical feedback signals AFB to be suppressed impinge on the acoustical port of the input converter 10 is specific. Therefore, at the beamformer unit 12, there is generated a beam characteristic B AFB , as shown in Fig. 4, which has minimum amplification for these specific angle or, as shown e.g. for an in-the-ear hearing device, at two specific angles ⁇ AFB .
  • B AFB beam characteristic B AFB
  • acoustical feedback AFB to be suppressed occurs substantially within a specific frequency band.
  • This frequency band is dependent, among others, on the specific output converter 16 used, the type of device e.g. in-the-ear or outside-the-ear device. Therefore, in a further improved embodiment, overall feedback suppression may be performed within that specific frequency band, thereby leaving beamforming in frequencies not within this specific frequency band unaffected and tailored according to needs different from acoustic feedback suppression.
  • beamforming B AFB for minimum amplification of acoustical feedback AFB to be suppressed is performed frequency selectively for frequencies f AFB of the acoustical feedback signal AFB.
  • Beamforming for frequencies f AFB which are not significantly present in the acoustical feedback AFB is performed by a second beamforming B AFB which may be selected independently from B AFB .
  • Frequency selective feedback compensation and adaptation beamforming may easily be realised, if at least beamforming in unit 12 as well as compensation in unit 18 are performed in frequency domain respectively in sub-bands. Beamforming is then realised at the frequencies f AFB with minimum amplification at the specific angles ⁇ AFB , whereas beamforming at other frequencies f AFB is performed according to other needs. Consequently the adaptation rate of beamforming in unit 12 is only controlled by the gain of compensator unit 18 at the frequencies f AFB .
  • beamforming B AFB may be maintained active to suppress feedback also in such "quiet" mode.
  • the loop gain, as estimated in compensator unit 18, may be compared with a threshold value and adaptation rate control at C 12R is only established, if the instantaneous loop gain at least reaches such threshold.
  • the control of the adaptation rate may then be lowered to practically zero, which means that beamforming is switched off for frequencies F AFB .
  • This establishes a hard on/off-switching of beamforming in the F AFB frequency-range.
  • such switching may be performed steadily which may be realised on the one hand by lowering the adaptation rate of B AFB steadily and/or by reducing beamforming amplification of B AFB steadily.
EP04010368A 2004-04-30 2004-04-30 Adaption automatique des microphones Withdrawn EP1489883A3 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2040486A2 (fr) * 2007-09-18 2009-03-25 Starkey Laboratories, Inc. Procédé et appareil pour la correspondance du microphone d'un appareil auditif directionnel portable utilisant la voix du porteur
EP2360951A1 (fr) * 2010-01-29 2011-08-24 Phonak Ag Procédé pour faire correspondre adaptativement les microphones d'un système d'écoute et système d'écoute

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002030150A2 (fr) * 2000-10-04 2002-04-11 Widex A/S Prothese auditive avec adaptation des transducteurs d'entree
US20020176587A1 (en) * 2001-05-23 2002-11-28 Hans-Ueli Roeck Method of generating an electrical output signal and acoustical/electrical conversion system
WO2003015460A2 (fr) * 2001-08-10 2003-02-20 Rasmussen Digital Aps Systeme de traitement sonore comprenant un generateur d'ondes a reponses de directivite et de gradient arbitraires

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002030150A2 (fr) * 2000-10-04 2002-04-11 Widex A/S Prothese auditive avec adaptation des transducteurs d'entree
US20020176587A1 (en) * 2001-05-23 2002-11-28 Hans-Ueli Roeck Method of generating an electrical output signal and acoustical/electrical conversion system
WO2003015460A2 (fr) * 2001-08-10 2003-02-20 Rasmussen Digital Aps Systeme de traitement sonore comprenant un generateur d'ondes a reponses de directivite et de gradient arbitraires

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2040486A2 (fr) * 2007-09-18 2009-03-25 Starkey Laboratories, Inc. Procédé et appareil pour la correspondance du microphone d'un appareil auditif directionnel portable utilisant la voix du porteur
EP2040486A3 (fr) * 2007-09-18 2010-10-20 Starkey Laboratories, Inc. Procédé et appareil pour l'adaptation du microphone d'un appareil auditif directionnel portable utilisant la voix du porteur
US8031881B2 (en) 2007-09-18 2011-10-04 Starkey Laboratories, Inc. Method and apparatus for microphone matching for wearable directional hearing device using wearer's own voice
US9210518B2 (en) 2007-09-18 2015-12-08 Starkey Laboratories, Inc. Method and apparatus for microphone matching for wearable directional hearing device using wearer's own voice
EP2360951A1 (fr) * 2010-01-29 2011-08-24 Phonak Ag Procédé pour faire correspondre adaptativement les microphones d'un système d'écoute et système d'écoute
US8588441B2 (en) 2010-01-29 2013-11-19 Phonak Ag Method for adaptively matching microphones of a hearing system as well as a hearing system

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