111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20110103626Al
`
`(19) United States
`c12) Patent Application Publication
`Bisgaard et al.
`
`(10) Pub. No.: US 2011/0103626 A1
`May 5, 2011
`(43) Pub. Date:
`
`(54) HEARING INSTRUMENT WITH ADAPTIVE
`DIRECTIONAL SIGNAL PROCESSING
`
`(75)
`
`Inventors:
`
`Nikolai Bisgaard, Lyngby (DK);
`Rob Anton Jurjen DE Vries,
`Tilburg (NL)
`
`(73)
`
`Assignee:
`
`GN RESOUND A/S, Ballerup
`(DK)
`
`(21)
`
`Appl. No.:
`
`12/306,515
`
`(22)
`
`PCTFiled:
`
`Jun.25,2007
`
`(86)
`
`PCTNo.:
`
`PCT/DK07/00308
`
`§ 371 (c)(l),
`(2), ( 4) Date:
`
`Mar. 27, 2009
`
`Related U.S. Application Data
`(60) Provisional application No. 60/816,244, filed on Jun.
`23,2006.
`
`(30)
`
`Foreign Application Priority Data
`
`Jun. 23, 2006
`
`(DK) ........................... PA 2006 00852
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`H04R 25100
`(52) U.S. Cl. ........................................................ 3811313
`
`ABSTRACT
`(57)
`A hearing instrument includes a signal processor, and at least
`two microphones for reception of sound and conversion of the
`received sound into corresponding electrical sound signals
`that are input to the signal processor, wherein the signal
`processor is configured to process the electrical sound signals
`into a combined signal with a directivity pattern with at least
`one adaptive null direction 8, and wherein the signal proces-
`sor is further configured to prevent the at least one null direc-
`tion 8 from entering a prohibited range of directions, wherein
`the prohibited range is a function of a parameter of the elec-
`trical sound signals.
`
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`
`Sony v. Jawbone
`
`U.S. Patent No. 8,321,213
`
`Sony Ex. 1010
`
`

`

`Patent Application Publication May 5, 2011 Sheet 1 of 2
`
`US 2011/0103626 A1
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`

`Patent Application Publication May 5, 2011 Sheet 2 of 2
`
`US 2011/0103626 Al
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`

`

`US 2011/0103626 AI
`
`1
`
`May 5, 2011
`
`HEARING INSTRUMENT WITH ADAPTIVE
`DIRECTIONAL SIGNAL PROCESSING
`
`RELATED APPLICATION DATA
`[0001] This application is the national stage of Interna-
`tional Application No. PCT/DK2007/000308, filed on Jun.
`25, 2007, which claims priority to and the benefit of Denmark
`PatentApplicationNo. PA2006 00852, filed on Jun. 23,2006,
`and U.S. Provisional Patent Application No. 60/816,244, filed
`on Jun. 23, 2006, the entire disclosure of all of which is
`expressly incorporated by reference herein.
`
`FIELD
`[0002] The present application relates to a hearing instru-
`ment, such as a hearing aid, an implantable hearing prosthe-
`sis, a head set, a mobile phone, etc, with a signal processor for
`directional signal processing.
`
`BACKGROUND
`[0003]
`It is well-known to use information on the directions
`to sound sources in relation to a listener for distinguishing
`between noise sources and desired sound sources. Through-
`out the present specification, the term directional signal pro-
`cessing system means a signal processing system that is
`adapted to exploit the spatial properties of an acoustic envi-
`ronment. Directional microphones are available, but typically
`directional signal processing systems utilize an array of
`onmi-directional microphones.
`[0004] The directional signal processing system combines
`the electrical signals from the microphones in the array into a
`signal with varying sensitivity to sound sources in different
`directions in relation to the array. Throughout the present
`specification, a plot of the varying sensitivity as a function of
`the direction is denoted the directivity pattern. Typically, a
`directivity pattern has at least one direction wherein the
`microphone signals substantially cancel each other. Through-
`out the present specification, such a direction is denoted a null
`direction. A directivity pattern may comprise several null
`directions depending on the number of microphones in the
`array and depending on the signal processing.
`[0005] Directional signal processing systems are known
`that prevent sound suppression of sources in certain direc-
`tions of interest.
`[0006] For example, U.S. Pat. No. 5,473,701 discloses a
`method of enhancing the signal-to-noise ratio of a micro-
`phone array with an adjustable directivity pattern, i.e. an
`adjustable null direction, for reduction of the microphone
`array output signal level in accordance with a criterion
`wherein the reduction is performed under a constraint that the
`null direction is precluded from being located within a pre-
`determined region of space.
`[0007]
`It is an object to provide a system with an improved
`capability of suppressing sound sources from all directions.
`
`SUMMARY
`[0008] According to the present application, the above-
`mentioned and other objects are fulfilled by a hearing instru-
`ment with at least two microphones for reception of sound
`and conversion of the received sound into corresponding elec-
`trical sound signals that are input to a signal processor,
`wherein the signal processor is adapted to process the elec-
`trical sound signals into a combined signal with a directivity
`pattern with at least one adaptive null direction 8. The signal
`
`processor is further adapted to prevent the at least one adap-
`tive null direction 8 from entering one or more prohibited
`ranges of directions, wherein each prohibited range is a func-
`tion of a parameter of the electrical sound signals.
`[0009] More than one prohibited range may for example
`occur in situations with more than one desired signal arriving
`from different directions.
`[0010] Preferably, the at least two microphones are omni-
`directional microphones; however in some embodiments,
`some of the at least two microphones are substituted with
`directional microphones.
`[0011]
`It is an important advantage that suppression of
`desired sound sources are avoided while undesired sound
`sources may still be suppressed from any arbitrary direction.
`[0012] The hearing instrument may further comprise a
`desired signal detector for detection of desired signals, for
`example a speech detector for detection of presence of
`speech. Adjustment of the prohibited range of directions may
`be performed gradually over a first time interval when desired
`signals, such as speech, are detected after a period of absence
`of speech.
`[0013] Further, adjustment of the prohibited range(s) of
`directions may be performed gradually over a second time
`interval when a desired signal, such as speech, stops after a
`period of presence of the desired signal, e.g. speech.
`[0014] The prohibited range may include a predetermined
`direction, such as oo azimuth or another preferred direction.
`[0015] An estimate of the power of sound received by at
`least one of the at least two microphones may constitute the
`parameter, for example the averaged power of sound received
`by a front microphone may constitute the parameter, or the
`parameter may be a function of the estimate of the power of
`sound, e.g. the averaged power of sound.
`[0016] An estimate of the signal to noise ratio of sound
`received by at least one of the at least two microphones may
`constitute the parameter, or the parameter may be a function
`of the estimate of the signal to noise ratio.
`[0017] The hearing instrument may further comprise a
`desired signal detector, such as a speech detector, and a direc-
`tion of arrival detector, and the prohibited range may include
`the detected direction of arrival of a detected desired signal,
`such as speech, whereby suppression of the desired signal, is
`prevented.
`[0018]
`In an embodiment with a single prohibited range,
`the prohibited range may, in the presence of multiple desired
`signal sources, such as multiple speech sources, include the
`detected direction of arrival of the detected desired signal
`source closest to oo azimuth, or another preferred direction.
`[0019]
`In an embodiment with a single prohibited range,
`the prohibited range may, in the presence of multiple desired
`signal sources, such as speech sources, include the detected
`directions of arrival of all desired signal sources.
`[0020]
`In an embodiment with a plurality of prohibited
`ranges, some or all of the prohibited ranges may be centered
`on respective detected directions of desired signal sources.
`[0021] As explained for a single prohibited range, the width
`of a specific prohibited range of the plurality of prohibited
`ranges centered on the corresponding direction of the corre-
`sponding desired signal source may be controlled as a func-
`tion of a parameter of the electrical sound signals, e.g. power,
`signal-noise ratio, etc.
`[0022] A current null direction may reside inside the pro-
`hibited range( s) of directions upon adjustment of the prohib-
`
`4
`
`

`

`US 2011/0103626 AI
`
`2
`
`May 5, 2011
`
`ited range(s) of directions. The signal processor may further
`be adapted to move such a null direction outside the adjusted
`prohibited range(s).
`[0023] The signal processor may be configured for sub band
`processing whereby the electrical sound signals from the
`microphones are divided into a set of frequency bands B, and,
`in each frequency band B, or at least in some of the frequency
`bands B, the electrical sound signals are individually pro-
`cessed including:
`[0024]
`(1) processing the electrical signals into a combined
`signal with an individual directivity pattern with an individu-
`ally adapted null direction 8,, and
`[0025]
`(2) preventing the null direction 8, from entering one
`or more prohibited ranges of directions, wherein each prohib-
`ited range is a function of a parameter of the electrical sound
`signals.
`[0026] Subband processing allows individual suppression
`of undesired sound sources emitting sound in different fre-
`quency ranges.
`[0027] The signal processor may be adapted to perform
`directional signal processing selected from the group consist-
`ing of an adaptive beam former, a multi -channel Wiener filter,
`an independent component analysis, and a blind source sepa-
`ration algorithm.
`[0028]
`In accordance with some embodiments, a hearing
`instrument includes a signal processor, and at least two micro-
`phones for reception of sound and conversion of the received
`sound into corresponding electrical sound signals that are
`input to the signal processor, wherein the signal processor is
`configured to process the electrical sound signals into a com-
`bined signal with a directivity pattern with at least one adap-
`tive null direction 8, and wherein the signal processor is
`further configured to prevent the at least one null direction 8
`from entering a prohibited range of directions, wherein the
`prohibited range is a function of a parameter of the electrical
`sound signals.
`
`DESCRIPTION OF THE DRAWING FIGURES
`[0029] The above and other features and advantages will
`become more apparent to those of ordinary skill in the art by
`describing in detail exemplary embodiments thereof with
`reference to the attached drawings in which:
`[0030] FIG. 1 shows a simplified block diagram of a digital
`hearing aid according to some embodiments, and
`[0031] FIG. 2 schematically illustrates the directional sig-
`nal processing of the hearing aid of FIG. 1.
`
`DETAILED DESCRIPTION
`[0032] The embodiments will now be described more fully
`hereinafter with reference to the accompanying drawings.
`The claimed invention may, however, be embodied in differ-
`ent forms and should not be construed as limited to the
`embodiments set forth herein. Thus, the illustrated embodi-
`ments are not intended as an exhaustive description of the
`invention or as a limitation on the scope of the invention. In
`addition, an illustrated embodiment needs not have all the
`aspects or advantages shown. An aspect or an advantage
`described in conjunction with a particular embodiment is not
`necessarily limited to that embodiment and can be practiced
`in any other embodiments even if not so illustrated. Like
`reference numerals refer to like elements throughout.
`[0033] FIG. 1 shows a simplified block diagram of a digital
`hearing aid according to some embodiments. The hearing aid
`
`1 comprises one or more sound receivers 2, e.g. two micro-
`phones 2a and a telecoil2b. The analog signals for the micro-
`phones are coupled to an analog-digital converter circuit 3,
`which contains an analog-digital converter 4 for each of the
`microphones.
`[0034] The digital signal outputs from the analog-digital
`converters 4 are coupled to a common data line 5, which leads
`the signals to a digital signal processor (DSP) 6. The DSP is
`programmed to perform the necessary signal processing
`operations of digital signals to compensate hearing loss in
`accordance with the needs of the user. The DSP is further
`programmed for automatic adjustment of signal processing
`parameters in accordance with some embodiments.
`[0035] The output signal is then fed to a digital-analog
`converter 12, from which analog output signals are fed to a
`sound transducer 13, such as a miniature loudspeaker.
`In addition, externally in relation to the DSP 6, the
`[0036]
`hearing aid contains a storage unit 14, which in the example
`shown is an EEPROM (electronically erasable programmable
`read-only memory). This external memory 14, which is con-
`nected to a common serial data bus, can be provided via an
`interface 15 with programmes, data, parameters etc. entered
`from a PC 16, for example, when a new hearing aid is allotted
`to a specific user, where the hearing aid is adjusted for pre-
`cisely this user, or when a user has his hearing aid updated
`and/or re-adjusted to the user's actual hearing loss, e.g. by an
`audiologist.
`[0037] The DSP 6 contains a central processor (CPU) 7 and
`a number of internal storage units 8-11, these storage units
`containing data and programmes, which are presently being
`executed in the DSP circuit 6. The DSP 6 contains a pro-
`gramme-ROM (read-only memory) 8, a data-ROM 9, a pro-
`gramme-RAM (random access memory) 10 and a data-RAM
`11. The two first-mentioned contain programmes and data
`which constitute permanent elements in the circuit, while the
`two last-mentioned contain programmes and data which can
`be changed or overwritten.
`[0038] Typically, the external EEPROM 14 is considerably
`larger, e.g. 4-8 times larger, than the internal RAM, which
`means that certain data and programmes can be stored in the
`EEPROM so that they can be read into the internal RAMs for
`execution as required. Later, these special data and pro-
`grammes may be overwritten by the normal operational data
`and working programmes. The external EEPROM can thus
`contain a series of programmes, which in some embodiments
`are used only in special cases, such as e.g. start-up pro-
`grammes.
`[0039] FIG. 2 schematically illustrates the signal process-
`ing of a hearing instrument according to some embodiments.
`The illustrated hearing instrument has two microphones 20,
`22 positioned in a housing to be worn at the ear of the user.
`When the housing is mounted in its operating position at the
`ear of the user, one of the microphones, the front microphone
`20, is positioned in front of the other microphone, the rear
`microphone 22, and a horizontal line extending through the
`front and rear microphones defines the front direction, i.e.
`azimuth=0°, corresponding to the looking direction of the
`user of the hearing instrument.
`[0040]
`In another embodiment comprising a binaural hear-
`ing aid, the microphones 20, 22 may be positioned in separate
`housings, namely a housing positioned in the left ear and a
`housing positioned in the right ear of the user. The directional
`signal processing may then take place in either of the left or
`right hearing aid housings, or in both housing, or in a separate
`
`5
`
`

`

`US 2011/0103626 AI
`
`3
`
`May 5, 2011
`
`housing containing signal processing circuitry and intended
`to be worn elsewhere on the body of the user. The electrical
`signals may be communicated between the housings with
`electrical wires or wirelessly. The large distance between
`microphones in the left ear housing and the right ear housing
`may lead to a directivity pattern with a large directivity.
`[0041] The microphones 20, 22 convert received sound
`signals into corresponding electrical sound signals that are
`converted into digital sound signals 24, 26 by respective AID
`converters (not shown).
`[0042] Each of the digitized sound signals 24, 26 is input to
`a respective subtraction circuit 28, and a respective delay 32,
`34 with delay DH" Each delay 32, 34 delays the digitized
`sound signal 24, 26 by the amount of time used by a sound
`signal to propagate in the oo azimuth direction from the front
`microphone 20 to the rear microphone 22. Each subtraction
`circuit 28, 30 subtracts the respective delayed signal 36, 38
`from one microphone 20, 22 from the direct signal 26, 24 of
`the other microphone 22, 20. Each of the subtracted signals
`40, 42 has a fixed directional pattern 44, 46, a so-called
`cardioid pattern. The cardioid pattern 44 of the upper branch
`(a) has a null direction 48 at 180° azimuth, i.e. pointing in the
`rear direction of the user, and the cardioid pattern 46 of the
`lower branch (b) has a null direction 50 at oo azimuth, i.e.
`pointing in the front direction of the user.
`[0043] The subtracted signal 42 of the lower branch (b) is
`filtered by an adaptive filter 52 with a transfer function H, and
`the subtracted signal40 of the upper branch (a) is delayed by
`a delay 54 with a delay DH equal to the group delay of the
`adaptive filter 52, and subsequently the two signals 56, 58 are
`subtracted for formation of a combined signal 60 with a
`directivity pattern 62 with an adaptive null direction 8. An
`example of a resulting directivity pattern 62 is also shown in
`FIG. 2. The hatched area of the resulting directivity pattern 62
`illustrates the prohibited range of directions which in the
`illustrated example is symmetrical around oo azimuth. The
`arched arrows indicate that the prohibited range of directions
`vary as a function of a parameter of the electrical sound
`signals.
`It should be noted that in the illustrated embodiment
`[0044]
`of FIG. 2, the delay 34 and the subtraction circuit 28 may be
`omitted and still an output 60 with a directional pattern 62
`similar to the illustrated embodiment of FIG. 2 may be
`obtained due to corresponding changes in the operation of the
`adaptive filter 52.
`[0045] Further, both delays 32, 34 and subtraction circuits
`28, 30 may be omitted in the illustrated embodiment of FIG.
`2, and still an output 60 with a directional pattern 62 similar to
`the illustrated embodiment of FIG. 2 may be obtained due to
`corresponding changes in the operation of the adaptive filter
`52.
`In the illustrated embodiment, the filter 52 is con-
`[0046]
`figured to minimize the output power of the combined signal
`60 by the filter coefficient update circuit 64. The filter 52 may
`be a finite impulse response (FIR) filter with N taps.
`[0047] The adaptive filter controller 66 prevents the null
`direction 8 from entering a prohibited range of directions as a
`function of a parameter of the electrical sound signals.
`[0048] The adaptive filter controller 66 constrains the filter
`coefficients of the adaptive filter 52 in such a way that a
`directional null 8 remains outside the prohibited range of
`directions.
`[0049] For example, the adaptive filter 52 may have a single
`tap in which case the adaptive filter 52 is an amplifier with a
`
`gain G H' and the adaptive filter controller 66 constrains the
`gain G H to remain inside the range O~G H~Glimir The value
`of the threshold Glimit determines the prohibited range of
`directions. For example, when Glimit=1, the prohibited range
`of directions ranges from -90° azimuth to +90° azimuth.
`[0050] The adaptive filter controller 66 may freeze the filter
`coefficients, i.e. updating of the filter coefficients may be
`stopped temporarily, when the strongest sound source is
`located within the prohibited range of directions. This
`approach requires estimation of the direction of arrival
`(DOA) of the signal incident on the hearing instrument.
`[0051] A DOA estimate may be obtained by determination
`of an M point auto-correlation A of the front microphone
`signal 24 delayed by D and determination of an M point
`cross-correlation B of the front microphone signal24 delayed
`by D and the rear microphone signal 26:
`
`M-1
`A=~ (front(k- D- i))2
`i=O
`
`M-1
`B = ~ front(k- D- i)rear(k- i)
`i=O
`
`(1)
`
`(2)
`
`~=B/A can be used as an estimate of the direction of arrival of
`the dominant sound in the acoustic environment. When ~=B/
`A=1, theDOAis 0°.As ~ decreasestowardO, theDOAmoves
`towards 180° azimuth. Thus, the adaptation may be tempo-
`rarily stopped when
`(3)
`i)>o
`where a is determined in such a way that ~=B/A=awhen the
`DOA of e.g. a zero mean white noise source is a degrees
`azimuth, the prohibited range of directions extending from
`-a degrees azimuth to a degrees azimuth including oo azi-
`muth.
`It should be noted that with this DOA estimate, the
`[0052]
`prohibited range of directions will be frequency dependent,
`because the value of~=B/ A is both dependent on the direction
`of arrival and on the frequency of the signal. In some embodi-
`ments, with sub band processing with individual beamform-
`ing in each frequency band B,, individual thresholds a may be
`defined for each frequency band B,.
`[0053] The person skilled in the art will recognize that
`numerous other conventional methods are available to obtain
`an estimate of the DOA, including frequency independent
`estimates.
`[0054] The signal processing is not necessarily done on the
`same apparatus that contains (one or more of) the micro-
`phones. The signal processing may be performed in a separate
`device that is linked to the, possibly multiple apparatuses that
`contain the microphones via a wire, wireless or other connec-
`tion.
`In the following various examples are described of
`[0055]
`determining the prohibited range of directions as a function of
`a parameter of the electrical sound signals. In the examples,
`-a till a degrees azimuth constitutes the prohibited range of
`directions including oo azimuth.
`In some embodiments, the prohibited range of
`[0056]
`directions is a function of the short term average power P F
`(e.g. over the past 10 seconds) of the electrical signal24 from
`front microphone 20 in accordance with
`
`6
`
`

`

`US 2011/0103626 AI
`
`4
`
`(4)
`
`May 5, 2011
`
`(7)
`
`[0057] Hence, the prohibited range of directions narrows
`when the signal power p F increases and for p ?P max a=0°
`(front direction) and for P p<P min a=amax·
`[0058] The values of am=' P mim andP maxmaybesetduring
`manufacture of the hearing instrument, or, during a fitting
`session of the hearing instrument with the intended user.
`[0059]
`In one example, Pmin=45 dBsPL and Pm==110
`dBsPL· It should be noted that very loud sounds (above 110
`dB sPL) may be suppressed from any direction providing pro-
`tection against harmful sounds (e.g. when getting too close to
`a loudspeaker at a concert). For amax=180°, an omni-direc-
`tional pattern is obtained in relative quiet environments below
`45 dBsPL·
`[0060]
`In other embodiments, the prohibited range of direc-
`tions is a function of the signal-to-noise ratio SNR for the
`signal 40 at point (a) in FIG. 2 in accordance with
`
`CY = CYmax
`
`max(SNRmim rnin(SNR, SNRmaxl)- SNRmin
`SNRmax - SNRmin
`
`(5)
`
`[0061] Hence, the prohibited range of directions narrows
`when the signal-to-noise ration SNR increases and for
`SNR>SNRm=' a=amax and for SNR<SNRmim a=Oo (front
`direction).
`[0062] The values of a max' SNRmin' and SNRmax may be set
`during manufacture of the hearing instrument, or, during a
`fitting session of the hearing instrument to the intended user.
`[0063] SNR may be estimated utilizing a speech detector
`68, e.g. a modulation or speech probability estimator, or a
`modulation or speech activity detector, to detect presence of
`speech and calculate the average power P xofthe signal when
`speech is present. The average noise power P N in absence of
`speech is estimated using a minimum statistics approach. An
`estimate of the SNR is then given by
`
`(6)
`
`In some embodiments, the prohibited range of
`[0064]
`directions is a function of the azimuth direction of speech ~.
`Presence of speech is detected by the speech detector 68 that
`processes the signal 24 and the direction of arrival ~ is esti-
`mated by the direction of arrival detector 70, and the prohib-
`ited range of directions is adjusted to include ~. ~may change
`due to head or speaker movement. In the presence of multiple
`speech sources, the prohibited range of directions may be
`adjusted to include DOA of the speech source closest to oo
`azimuth or to include DOAs of all detected speech sources.
`[0065] The above-mentioned approaches may be com-
`bined.
`[0066] For example, in some embodiments, the prohibited
`range of directions is a function of the short term average
`power P F (e.g. over the past 10 seconds) of the electrical
`signal 24 from front microphone 20 in accordance with
`
`which is similar to equation ( 4) above with the exception that
`a varies between amax and asnr in equation (7) while a varies
`between amax and 0° in equation (4), and wherein
`
`CYsnr =
`
`and
`
`max(SNRtowthtd• rnin(SNR, SNRtnw))- SNRtow
`SNRtowthld- SNRtow
`
`(1 80- a:m;n)
`
`(8)
`
`(9)
`
`wherein
`SNR is the estimated signal-to-noise ratio at point (a) in FIG.
`1 over the past 10 seconds, e.g. obtained as described above,
`SNRshort is the estimated signal-to-noise ratio at point (a) in
`FIG. 1 over the past 0.05 seconds, e.g. obtained as described
`above,
`SNRshortmax is the maximum value of SNRshort over the past
`1 0 seconds, and
`DOAmax is the average value of the DOA over the 0.05 sec-
`onds block that resulted in SNRshortmax·
`[0067] For example, Pmax=60 dBsPD Pmin=45 dBsPD
`SNRmin=5 dB, SNRmax=15 dB, SNRzow=-10 dB, SNR-
`zowthid=-20 dB, and amax=180°.
`[0068]
`It should be noted that in this embodiment the pro-
`hibited range of directions is as narrow as possible around the
`direction to the speech source with the highest SNR. The
`prohibited range increases when the overall SNR is larger
`than the threshold SNRmin or smaller than the threshold SNR-
`low' and saturates into an onmi-directional pattern when the
`SNR is larger than the threshold SNRmax (e.g. when there is
`no noise) or lower than the threshold SNRzowthid (e.g. when
`there is no speech), or the overall signal power P F is smaller
`than the threshold p max' and also saturates into an omni-
`directional pattern when P F is smaller than the threshold P min
`(e.g. in quiet surroundings).
`[0069] Preferably, timing restrictions are also included in
`accordance with some embodiments so that frequent and
`abrupt changes of the prohibited range of directions are
`avoided.
`[0070] For example the prohibited range of directions may
`be prevented from narrowing in response to a short term
`presence of a noise source, such as reception of reverbera-
`tions. Short term presence may be defined as presence during
`less than 0.1 seconds.
`[0071] An adjustment of the prohibited range of directions
`may be performed gradually in a time interval when speech
`stops after a period of presence of speech. For example, a may
`be gradually increased to amax in a time interval of about 3
`seconds. Throughout the present specification, presence or
`absence of speech refer to the detection or non-detection of
`speech, respectively, of the system.
`[0072] A speech stop may be defined as the moment that no
`speech has been detected for e.g., 5 seconds, and a conversa-
`tion stop may be defined as the moment that no speech has
`
`7
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`US 2011/0103626 AI
`
`May 5, 2011
`
`5
`
`been detected for e.g., 30 seconds. Speech start and conver-
`sation start may be defined as the moment that speech is
`detected for the first time after a speech stop and a conversa-
`tion stop, respectively.
`[0073] A long term average may be defined as the average
`over e.g., 2 seconds. A short term average may be defined as
`the average over e.g., 50 milliseconds.
`In some embodiments, the prohibited range of
`[0074]
`directions is adjusted upon start of conversation according to
`the following:
`[0075] Calculation of the long term average DOA value
`during speech presence is performed; typically the calcula-
`tion requires 2 seconds of speech presence.
`[0076] Provided that the long term average DOA value
`during speech presence is not significantly different from the
`long term average DOA value during speech absence, a is
`increased to amax with the release time, e.g. in about 3 sec-
`onds. (This situation occurs when e.g. the noise and speech
`arrive from the same direction, in which case beamforming is
`not advantageous, or when the speaker is outside the Hall
`radius and the perceived noise field is diffuse, or when the
`SNRis low.)
`[0077] Provided that the long term average DOA value
`during speech presence is significantly different from the
`long term average DOA value during speech absence, the
`prohibited range of direction is adjusted in accordance with
`the following:
`[0078] When the short term average DOA value during
`speech presence remains above or around e.g. 80°, a is
`increased to amax in about 3 seconds. (In this case the listener
`is apparently not interested enough in the speech to turn his
`head, or he is e.g. driving a car and can not turn his head to the
`speaker.)
`[0079] When the short term average DOA value during
`speech presence does become significantly lower than 80°,
`the prohibited range of directions is adjusted to just include
`the minimum of the short term average DOA value over e.g.
`the past 2 seconds, plus a safety margin of about 20° in order
`to take head movements into a account. This is repeated until
`speech stop. Upon speech stop, a is adjusted to e.g. <Pmax+20°,
`where <Pmax is equal to the maximum of the short term average
`DOA values measured at a speech start over e.g. the last 3
`speech start events. (This prevents the user from missing any
`of the speech of interest, while a narrow beam is also obtained
`when the user has focused on the speaker. A situation like this
`can occur when the user is in a restaurant and is alternatively
`looking at the plate and at the person next or opposite to the
`user.)
`In the above example, preferably amax is 180° so
`[0080]
`is
`that an onmi-directional pattern is obtained when a
`increased to amax' since the onmi-directional pattern imparts
`a perception to the user of being connected to the environ-
`ment.
`[0081] amax equal to 90° maybe selected to maintain direc-
`tional suppression in the back region of the user.
`[0082] The prohibited range of directions may be broad-
`ened to such an extent that an existing null direction 8 ends up
`residing within the prohibited range.
`[0083] According to an aspect of some of the embodiments,
`the signal processor is adapted to move a null direction 8
`residing within a prohibited range for a certain time period,
`e.g. 1 second, or 10 seconds, outside the prohibited range.
`This may be done momentarily or over a period of time.
`
`[0084] A null position monitor may be provided for moni-
`toring the current null position. When the current null posi-
`tion resides within the adapting prohibited range of directions
`for more than, e.g., 1 second, the signal processor moves the
`null outside the prohibited range of directions.
`[0085] An estimate of the current null position may be
`obtained by averaging the direction of arrival during adapta-
`tion. When the rate of change of this average is similar to the
`rate of adaptation of the null, the average will be a good
`estimate of the current null position.
`[0086] The null may be moved outside the prohibited range
`of directions in many ways. For example, when the null
`resides within the prohibited range of directions for more
`than, e.g., 1 second, the adaptive filter H may be re-