Method and device for frequency-selective processing of an audio signal with low latency

A method for processing an input audio signal includes using a first analytical filter bank to divide the input audio signal in a first frequency splitting process into a plurality of first frequency bands. The first frequency bands of a first subgroup are divided in a further frequency splitting process by a further analytical filter bank into a plurality of frequency subbands. The divided input audio signal is frequency-selectively processed or amplified. The divided and processed input audio signal is then combined again into an output audio signal. A prediction is applied to the first frequency bands of the first subgroup and/or the frequency subbands derived therefrom, to compensate for latency differences between the first frequency bands and the frequency subbands as a result of the or each further frequency splitting process. A device or hearing aid for carrying out the method is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2021 205 251.7, filed May 21, 2021; the prior application is herewith incorporated by reference in its entirety.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a method for processing an input audio signal, in particular in a hearing aid, wherein:the input audio signal is divided into a plurality of first frequency bands in a first frequency splitting process by using a first analytical filter bank,the first frequency bands of a first subgroup of the first frequency bands is divided into a plurality of frequency subbands in at least one further frequency splitting process by using at least one further analytical filter bank,the input audio signal that is divided into the first frequency bands or the frequency subbands, is processed, in particular amplified, in a frequency-selective manner, andthe input audio signal that is divided into the first frequency bands or the frequency subbands and processed in a frequency-selective manner is then combined again into an output audio signal.

The invention also relates to a device, in particular in a hearing aid, including:a first analytical filter bank configured to divide the input audio signal into a plurality of first frequency bands in a first frequency splitting process,at least one further analytical filter bank downstream of the first analytical filter bank, configured to divide the first frequency bands of a first subgroup of the first frequency bands into a plurality of frequency subbands in at least one further frequency splitting process,a signal processing unit for frequency-selective processing, in particular amplification, of the input audio signal that has been divided into the first frequency bands or the frequency subbands, anda synthetic filter bank apparatus downstream of the signal processing unit, configured to combine the input audio signal that has been divided into the first frequency bands or the frequency subbands and processed in a frequency-selective manner into an output audio signal.

Such a method and such a device are known from European Patent EP 2 124 335 B1, corresponding to U.S. Pat. No. 8,150,081. The device is in particular a hearing aid.

The terms “hearing aid” or “hearing apparatus” generally refer to an electronic device that assists the hearing capacity of a person (referred to below as the “wearer” or “user”) who is wearing the hearing aid. The invention relates in particular to hearing aids that are configured to fully or partially compensate for hearing loss of a user with impaired hearing. Such a hearing aid is also known as a “hearing device.” In addition, there are hearing aids that protect or improve the hearing capacity of users with normal hearing, for example to enable an improved understanding of speech in complex hearing situations. Hearing aids further also include headphones or other sound reproduction devices that submerge an environmental noise in another audio signal (e.g. music or a telephone conversation) or that reduce the perceptibility of the environmental noise through active noise suppression.

Hearing aids in general, and hearing devices in particular, are in most cases configured to be worn at the head and in this case, in particular, in or at an ear of the user, in particular as a “behind the ear” (BTE) device or as an “in the ear” (ITE) device. In terms of their internal structure, hearing aids generally include at least one (acousto-electric) input transducer, a signal processor and an output transducer. During operation of the hearing aid, the, or each, input transducer receives airborne sound from the environment of the hearing aid and converts this airborne sound into an input audio signal (i.e. an electrical signal that transports the information regarding the environmental sound). The input audio signal or signals is or are processed in the signal processor (i.e. modified in respect of its sound information) in order to assist the hearing capacity of the user, in particular in order to compensate for a hearing loss of the user. The signal processing unit outputs a correspondingly processed audio signal (also known as the “output audio signal” or “modified sound signal”) to the output transducer.

In most cases, the output transducer is configured as an electro-acoustic transducer that converts the (electrical) output audio signal again into airborne sound, wherein this airborne sound—which has been modified in comparison with the environmental sound—is output into the hearing canal of the user. In the case of a hearing aid worn behind the ear, the output transducer, also known as the “earphone” (or “receiver”), is usually integrated into a housing of the hearing aid outside the ear. The sound that is output from the output transducer is guided in this case into the hearing canal of the user by using a sound tube. As an alternative to this, the output transducer can also be disposed in the hearing canal, and thus outside the housing that is worn behind the ear. Such hearing aids are also referred to as RIC devices (for “receiver in canal”). Hearing aids worn in the ear, having dimensions which are so small that they do not protrude outside above the hearing canal, are also referred to as CIC devices (for “completely in canal”).

In further configurations, the output transducer can also be implemented as an electromechanical transducer that converts the output audio signal into structure-born sound (vibrations), wherein this structure-born sound is, for example, output into the skull bone of the user. There are, furthermore, implantable hearing aids, in particular cochlear implants, and hearing aids having an output transducer which directly stimulates the auditory nerve of the user.

For the purposes of signal processing, the input audio signal is regularly divided in a hearing aid into a plurality of frequency bands by using an analytical filter bank. In other words, the input audio signal is converted into a plurality of partial band signals that are passed, separately from one another, into frequency channels, each of which is processed, in particular amplified, in a specific manner. By using a synthetic filter bank, the processed partial band signals are then again assembled into the output audio signal including all the frequency components.

An important aspect of the processing of an audio signal, in particular in a hearing aid, is, on the one hand, the latency, i.e. the time delay of the audio signal caused by the processing. The latency should appropriately be less than 10 milliseconds (ms), since a greater latency would noticeably impair the hearing experience of a human user of the hearing aid. On the other hand, for some, signal processing functions such as, for example, noise reduction or dynamic compression, a high frequency resolution is helpful, i.e. a division of the audio signal into a large number of frequency bands each having only a narrow bandwidth.

Those two demands, however, conflict with one another, since the product of time and frequency resolution is constant (Küpfmüller's uncertainty principle). In practice, the minimum technically appropriate bandwidth is thus limited by the maximum tolerable latency, as a result of which in some cases a satisfactory signal processing is made more difficult or is prevented.

Thus, for example, for a good noise reduction of voiced speech, a frequency interval between adjacent frequency bands that corresponds to at most half of the fundamental frequency would be desirable. Even for female voices, in which the fundamental frequency of voiced sounds lies typically between 200 hertz (Hz) and 300 Hz, the desirable frequency interval of between 100 Hz and 150 Hz can, however, not be achieved, since it would be associated with too high a latency. In conventional hearing aids, therefore, an acceptable, though not fully satisfactory, compromise between the highest possible frequency resolution and the lowest possible latency of between 200 Hz and 500 Hz is typically realized.

Filter banks in which the frequency bands have a non-uniform frequency interval, namely increasing continuously or in steps with rising frequency, are sometimes employed to solve this problem. A two-stage analytical filter bank apparatus for a hearing apparatus is thus disclosed in European Patent EP 2 124 335 B1, corresponding to U.S. Pat. No. 8,150,081, in which the audio signal to be processed is divided by a first filter bank into four first frequency bands and then further into 24 second frequency bands by second filter bank. Of the 24 second frequency bands, the lower 12 frequency bands have a significantly lower frequency interval and a lower bandwidth than the upper 12 frequency bands.

As a result of the non-uniform frequency distribution of the known analytical filter bank apparatus, the disadvantages resulting from the high frequency-splitting are reduced, since an increased latency only occurs in a partial region of the sound spectrum. This advantage is, however, obtained at the cost of a poorer sound quality, since the output audio signal is distorted as a result of different, greater latencies and different group transit times in the low-frequency and high-frequency frequency channels. In addition, each partial band in non-uniform filter banks typically has a different bandwidth. A possible under-sampling must, however, be oriented to the band with the highest bandwidth. This gives rise to a comparatively ineffective signal processing.

On the other hand, a method and a device for processing an audio signal in a hearing aid is described in European Patent Application EP 3 197 181 A1, corresponding to U.S. Pat. No. 10,142,741, wherein a plurality of signal blocks are formed in the time domain from the input audio signal. These time blocks are at least partially predicted in order to reduce the latency; in other words, the progress of the signal in these time blocks is extrapolated into the future. The predicted time blocks are then divided by the filter bank into frequency bands, and thus transformed into the frequency domain. As a result of the prediction, however, the known method also leads to a noticeable impairment of the sound quality.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method and a device for frequency-selective processing of an audio signal with low latency, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which enable a frequency-selective processing of an audio signal with low latency and high (sound) quality. A high frequency-resolution should be enabled in this case, in particular in a partial region of the audible sound spectrum.

With the foregoing and other objects in view there is provided, in accordance with the invention, a method for (frequency-specific) processing of an audio signal, in particular in a hearing aid, in which the input audio signal is first divided spectrally in a first analytical filter bank into a plurality of first frequency bands (first frequency splitting process). A first subgroup (subset) of the first frequency bands is divided in at least one further frequency splitting process by using at least one further analytical filter bank into frequency subbands (with narrower bandwidths than the first frequency bands). The input audio signal that is divided into the first frequency bands and, if relevant, in the frequency subbands, is processed, in particular amplified, in a frequency-selective manner. The input audio signal that is divided into the first frequency bands and, if relevant into the frequency subbands, and processed in a frequency-selective manner, is then combined again into an output audio signal.

According to the invention, a prediction is now applied to the more finely split part of the input audio signal (and preferably only to this part of the input audio signal), that compensates for, i.e. completely eliminates or at least reduces, a latency caused by the, or each, further frequency splitting process. In other words, latency differences between the frequency bands and the frequency subbands resulting from the, or from each, further frequency splitting process are compensated for by the prediction. In particular, the latency of the more finely frequency-divided part of the input audio signal is matched to the lower latency of a part of the input audio signal having a frequency which has been divided more coarsely.

In contrast to the method known from European Patent Application EP 3 197 181 A1, corresponding to U.S. Pat. No. 10,142,741, the prediction is applied in this case in the frequency domain. There exists a number of variant embodiments within the framework of the invention for the time point or the location at which the prediction is applied within the frequency domain. The prediction is thus either applied directly to the frequency-subbands and/or to those first frequency bands from which the frequency subbands are derived. The prediction can in this case be performed either before or after the signal processing, or even between two of in such a way that may be a plurality of processing steps. In the context of the invention the prediction can, finally, also take place in a plurality of sequential prediction steps.

A particularly fine frequency splitting process is enabled by the method described above in a partial region of the sound spectrum, while at the same time the distortion of the output signal normally entailed by non-uniform frequency splitting processes is avoided or at least reduced by the prediction. In comparison with the method known from European Patent Application EP 3 197 181 A1, corresponding to U.S. Pat. No. 10,142,741, however, the disadvantageous effect of the prediction on the sound quality is also reduced, since the prediction is only applied to a partial region of the sound spectrum. Overall, therefore, a high-frequency resolution in one partial region of the sound spectrum is achieved in combination with a particularly good sound quality.

In one preferred embodiment of the method, the frequency splitting process is carried out in two stages. A first subgroup (subset) of the first frequency bands is split in this case in a second frequency splitting process using a second analytical filter bank more finely into second frequency bands (i.e. frequency subbands of the second stage). Each first frequency band of the first subgroup is thus divided again into a plurality of these second frequency bands. The prediction is applied in this case to the second frequency bands, or to the first frequency bands of the first subgroup, in order to compensate for the latency caused by the second frequency split.

The basic concept of the method according to the invention, namely the finer frequency splitting process of a spectral part of the input audio signal, associated with a prediction of this more finely split spectral region to compensate for the latency caused by the finer frequency splitting process, is optionally extended to n-stage frequency splits (with n=3, 4, 5 . . . ). In general in this case, a subgroup of the i-th frequency bands (where i=2, 3, 4 . . . ) is subdivided into (i+1)th frequency bands of even narrower bandwidth. That part of the input audio signal that has been frequency-divided multiple times is in this case predicted in each case in the frequency domain in such a way that the latency caused by the multiple frequency division is compensated for in each case.

Thus, in a three-stage implementation of this method principle, each of the second frequency bands of a subgroup of the second frequency bands is divided in a third frequency splitting process by using a third analytical filter bank into a plurality of third frequency bands (i.e. frequency subbands of the third stage). The prediction is applied in this case to the third frequency bands and/or to the second frequency bands from which the third frequency bands have been derived, and/or to the first frequency bands from which the third frequency bands have been derived, in such a way that the latency caused by the second and third frequency splitting processes is compensated for.

The first subgroup of the first frequency bands is preferably selected in such a way that it covers a contiguous low-frequency range of the sound spectrum, in particular the bottom 2 to 3 kHz of the sound spectrum. The first subgroup of the first frequency bands is, in other words, preferably formed of a plurality of the first frequency bands having respective center frequencies which are immediately adjacent and that include the lowest first frequency band. This is particularly advantageous, in particular for processing audio signals that contain human speech. This is because on the one hand, the sound components of speech sound, in particular in the case of voiced sounds, dominate in this low frequency range, and on the other hand, the frequency resolution of human hearing is also particularly high at low frequencies.

Fundamentally, the method can be employed with a conventional multi-stage filter bank as is, for example, known from European Patent EP 2 124 335 B1, corresponding to U.S. Pat. No. 8,150,081. Preferably, the, or each, further analytical filter bank, however, only acts on the first subgroup of the first frequency bands. A second subgroup of the first frequency bands is, on the other hand, preferably subjected to the frequency-selective processing, in particular amplification, without any further frequency splitting process. On the whole, a particularly low latency is achieved in this way.

A particularly efficient frequency splitting process and processing of the input audio signal is achieved in an advantageous embodiment of the invention in that the first frequency bands have a consistent first bandwidth, i.e. one that is the same for all the first frequency bands. For the same reason—additionally or alternatively—the i-th frequency bands (where i=2, 3 . . . ) are preferably so configured that these i-th frequency bands each have a consistent bandwidth, i.e. one that is the same for all of the i-th frequency bands. The first bandwidth in this case is, in particular, an integral multiple of the second bandwidth; the second bandwidth, if it exists, is an integral multiple of the third bandwidth, and so forth.

Basically, the part of the input audio signal that is more finely divided in frequency is predicted linearly in the context of the invention. Preferably, however, the prediction applied to the first frequency bands of the first subgroup, or the frequency subbands derived therefrom, is a non-linear prediction.

In a particularly advantageous variant embodiment of the invention, one or more prediction algorithms are employed that can be adapted while the method is running, i.e. during the signal processing. In contrast to prediction algorithms that are configured or trained in advance, which are not adaptive (static) while the method is running, adaptive prediction algorithms are, on the one hand, very flexible and, on the other hand, sparing with resources and therefore particularly suitable for use in a hearing aid.

In appropriate embodiments of the invention, in particular at least one Hammerstein model, a recurrent neural network and/or an echo-state network is employed to carry out the prediction.

In order to reduce the negative influence of the non-uniform frequency splitting processes of the input audio signal and of the prediction of the sound quality of the output signal altogether much further, the method described previously is, in a development of the invention, only employed at certain times in situations in which it brings particular advantages, namely, in particular, when processing noise that contains voiced speech. The input audio signal is analyzed—across all frequency bands or in specific bands—for the presence of voiced speech for this purpose. The, or each, further frequency splitting process, and therefore also the prediction, are only performed on the signal path that leads to the output audio signal in at least one of the first frequency bands or frequency subbands when the presence of voiced speech is detected in the input audio signal. The, or each, further frequency splitting process and/or the prediction can optionally, however, also continue in the background of the signal processing in the absence of voiced speech without this having an effect on the output audio signal.

In addition or as an alternative, the accuracy (reliability) of the prediction can be ascertained for the same purpose—across all frequency bands or in specific bands. On the path leading to the output signal, the finer frequency splitting process of a portion of the input audio signal (i.e. the derivation of the frequency subbands), and therefore also the prediction, is again only performed in at least one of the first frequency bands or frequency subbands when the accuracy of the prediction satisfies a predefined criterion there, in particular exceeds a predefined threshold value. The, or each, further frequency splitting process and/or the prediction can optionally, however, also continue in the background of the signal processing when the prediction is inadequate, without this having an effect on the output audio signal.

With the objects of the invention in view, there is also provided a device for processing an input audio signal, in particular in a hearing aid, which includes an analytical filter bank apparatus with a first analytical filter bank and at least one further analytical filter bank. The first analytical filter bank is configured to divide the input audio signal into a plurality of first frequency bands. The at least one further analytical filter bank is downstream of the first analytical filter bank and is configured to divide each first frequency band of a first subgroup of the first frequency bands into a plurality of frequency subbands. As described above, the analytical filter bank apparatus optionally includes, in addition to a second analytical filter bank, a third analytical filter bank, further downstream, that splits the one subgroup of the second frequency bands yet more finely into third frequency bands as well, potentially, as yet one or multiple further downstream analytical filter banks.

The device further includes a signal processing unit for frequency-selective processing, in particular amplification, of the input audio signal divided into the first frequency bands or the frequency subbands, as well as a synthetic filter bank apparatus downstream of the signal processing unit that is configured to combine the input audio signal that has been divided into the first frequency bands and, where relevant, the frequency subbands, and processed in a frequency-selective manner to form an output audio signal.

According to the invention, the device includes at least one predictor that is configured to apply a prediction to the first frequency bands of the first subgroup and/or the frequency subbands derived from them, in order to compensate for latency differences between the first frequency bands and the frequency subbands as a result of the, or each, further frequency splitting process.

The signal processing unit is preferably implemented in a digital signal processor of the hearing aid. The signal processing unit can be realized within the context of the invention in the form of (non-programmable) electronic circuits. In this case the signal processor is configured, for example, as an ASIC or includes such a circuit. The signal processing unit is, alternatively, realized in the form of software. In this case, the signal processor is formed of a programmable electronic component. As a further alternative to this, the signal processing unit is formed by a combination of non-programmable circuits and software. The signal processor in this case is formed by a hybrid chip that includes at least one programmable component and at least one non-programmable component.

The synthetic filter bank apparatus is preferably configured with mirror symmetry to the analytical filter bank apparatus, and thus includes a corresponding counterpart for each analytical filter bank. The synthetic filter bank apparatus includes in particular a second synthetic filter bank that combines the second frequency bands after the signal processing again into first frequency bands, as well as a first synthetic filter bank that combines the first frequency bands into the output signal. In embodiments in which the analytical filter bank apparatus includes more than two analytical filter banks, the synthetic filter bank also preferably includes a corresponding plurality of synthetic filter banks.

The device according to the invention is in general provided and configured for automatically carrying out the method according to the invention described above. The embodiments and developments of the method described above correspond in this case to equivalent embodiments and developments of the apparatus. The embodiments of necessary and optional features of the method and their respective effects and advantages are therefore transferable to the device, and vice versa.

In preferred embodiments, the device is thus configured in such a way that:a second subgroup of the first frequency bands is supplied directly to the signal processing unit in order to subject the second subgroup of the first frequency bands to the frequency-selective processing without any further frequency splitting process,the first frequency bands and/or the subsidiary bands of the i-thstage (where I=2, 3, 4 . . . ) have a consistent first or i-thbandwidth, wherein the first bandwidth is in particular an integral multiple of the second bandwidth, and so forth,the at least one predictor is non-linear, and/orthe at least one predictor is adaptive at runtime, i.e. during the signal processing.The apparatus optionally includes a speech detection module that is configured to analyze the input audio signal for the presence of voiced speech, as well as a switching apparatus referred to as a “signal diverter” that is configured only to activate the, or each, further analytical filter bank when the voice detection module detects the presence of voiced speech in the input audio signal.

Alternatively or in addition, the device includes a switching apparatus (signal diverter) that is identical to or different from the switching apparatus described above, that is configured to activate and deactivate the, or each, further analytical filter bank depending on the accuracy (reliability) of the prediction. The accuracy of the prediction can basically be ascertained in the context of the invention by the switching apparatus itself by analyzing each of the partial band signals supplied to the first subgroup in the first frequency bands. Preferably however, a characteristic magnitude is ascertained by the, or each, predictor for the accuracy of the prediction, and is output to the switching apparatus that activates and deactivates the second analytical filter bank depending on this magnitude. In particular, a so-called “prediction gain” is employed as the characteristic magnitude for the accuracy of the prediction.

The analytical filter bank apparatus, the synthetic filter bank apparatus, the, or each, predictor and—if present—the speech detection module and/or the, or each, switching apparatus are preferably integrated into the signal processor of the device in the form of (non-programmable) hardware and/or software. In particular, the, or each, switching apparatus can, in the context of the invention, also be a software module.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the figures of the drawings, in which parts and values that correspond to one another are always given the same reference signs, and first, particularly, toFIG.1thereof, there is seen, as an example for a device according to the invention for processing an audio signal, a hearing device2, i.e. a hearing aid configured to assist the hearing capacity of a user with impaired hearing. In the example illustrated herein, the hearing device2is a BTE hearing device that can be worn behind an ear of a user.

The hearing device2includes at least one microphone6as an input transducer and one earphone8as an output transducer inside a housing4. The hearing device2further includes a battery10and an (in particular digital) signal processor12. Preferably the signal processor12includes both a programmable subunit (a microprocessor, for example) as well as a non-programmable subunit (an ASIC, for example).

The signal processor12is supplied with an electrical supply voltage U from the battery10.

In normal operation of the hearing device2, the microphone6receives airborne sound from the environment of the hearing device2. The microphone6converts the sound into an (input) audio signal I which contains information about the received sound. The input audio signal I is supplied to the signal processor12inside the hearing device2, which modifies this input audio signal I to assist the hearing capacity of the user.

The signal processor12outputs an output audio signal O, which contains information about the processed and thereby modified sound, to the earphone8.

The earphone8converts the output sound signal O into modified airborne sound. This modified airborne sound is transferred into the auditory canal of the user through a sound channel14that connects the earphone8to a tip16of the housing4, as well as through a flexible sound tube (not shown explicitly) that connects the tip16to an earpiece inserted into the auditory canal of the user.

The functional structure of the signal processor12is illustrated in more detail inFIG.2.

In a manner not shown in detail, the input audio signal I recorded by the microphone6is first digitized by an analog-digital converter integrated into the signal processor12or upstream of the signal processor12. The digitized input audio signal I is first supplied inside the signal processor12to an analytical filter bank apparatus20which, in the example illustrated inFIG.2, includes a first analytical filter bank22and a second analytical filter bank24downstream thereof.

By using the first analytical filter bank22, the input audio signal I is divided in a first frequency splitting process into a plurality of first frequency bands26, i.e. first frequency channels, each of which carries a partial band signal of the input audio signal I. For simplicity, just four first frequency bands26are illustrated inFIG.2. In a useful practical implementation of the invention, the first analytical filter bank22divides the input audio signal I into, for example, 32 first frequency bands26. The frequency bands26have a consistent (first) bandwidth of, for example, 500 Hz, and a consistent spectral spacing of 250 Hz.

The second analytical filter bank24only acts on a (first) subgroup28of the frequency bands26, covering a range from 2 to 3 kHz at the low-frequency edge of the sound spectrum. The subgroup28in this case includes a number of adjacent frequency bands26that contain the lowest (i.e. lowest frequency) first frequency band26. In the example illustrated inFIG.2, the subgroup28includes, for example, the bottom two of the total of four frequency bands26. In the practical implementation, the subgroup28includes, for example, the bottom 12 of the total of 32 first frequency bands26.

Each first frequency band26of the subgroup28is split by the second analytical filter bank24in a second frequency splitting process into multiple (for example, into two, according toFIG.2) second frequency bands30. The frequency bands30have a consistent (second) bandwidth of, for example, 125 Hz, and a consistent spectral spacing of 62.5 Hz.

A second subgroup32of the frequency bands26, which does not belong to the high-frequency frequency bands26belonging to the subgroup28, bypasses the second analytical filter bank24and is thus not subject to a second (and finer) frequency splitting process.

The respective partial band signals of the high-frequency frequency bands26of the subgroup32, as well as the frequency bands30, are processed (i.e. signal-modified) in a signal processing unit34. In the course of this processing, the respective partial band signal of one of the frequency bands26of the subgroup32, as well as one of those frequency bands30, are in particular amplified in accordance with an individual (i.e. with a predefined specific frequency) amplification factor. For the purposes of efficient signal processing, the signal processing unit34in the example according toFIG.2includes two subunits36and38for the high-frequency frequency bands26of the subgroup32, or for the frequency bands30, wherein the subunits36and38are each specifically configured for the different bandwidths of the supplied frequency bands26or30respectively.

The processed partial band signals of the high-frequency frequency bands26of the subgroup32and the frequency bands30are combined to form the output audio signal O by a synthetic filter bank apparatus40. The synthetic filter bank apparatus40is configured with mirror symmetry to the analytical filter bank apparatus20. It accordingly includes a second synthetic filter bank42that combines the second frequency bands30again to form the first frequency bands26of the subgroup28, as well as a first synthetic filter bank44that combines the first frequency channels26of the first subgroup28and of the subgroup32to form the output audio signal O.

Through the finer frequency splitting process performed by using the analytical filter bank24, a latency difference occurs between the low-frequency partial band signals of the frequency bands26of the subgroup28as compared with the high-frequency partial band signals of the frequency bands26of the subgroup32, which would, in the absence of further measures, lead to a distortion of the output audio signal O.

In order to compensate for this latency difference (i.e. to eliminate it entirely or at least to reduce it) a predictor46is connected into the signal path of the frequency bands30. The predictor46is preferably configured as a non-linear predictor that is continuously adaptable during operation of the hearing device2, in particular as a Hammerstein model. The predictor46has parameters specifically adapted to each supplied frequency band30.

In contrast to the method known from European Patent Application EP 3 197 181 A1, corresponding to U.S. Pat. No. 10,142,741, the prediction in the hearing device2takes place in the frequency domain, and is applied exclusively to the more finely frequency-divided low-frequency part of the sound spectrum. In the frequency domain, i.e. between the first analytical filter bank22and the first synthetic filter bank44, the predictor can, however, be disposed at various positions. In the example according toFIG.2, the predictor46is connected between the second analytical filter bank24and the subunits38of the signal processing unit34. InFIG.2, furthermore, three alternative positions are given for the predictor (indicated therein with the reference signs46′), namely:between the first analytical filter bank22and the second analytical filter bank24,between the subunit38of the signal processing unit34and the second synthetic filter bank42, andbetween the second synthetic filter bank42and the first synthetic filter bank44.

In one possible modification of the embodiment illustrated inFIG.2, the hearing device2contains multiple predictors46,46′ connected in series, disposed in particular at a plurality of the positions given in feet.2, each compensating for a part of the latency difference described above.

The output audio signal O output from the first synthetic filter bank44is converted back into an analog signal by a digital-analog converter (not shown in more detail) that is integrated into the signal processor12or is downstream of the signal processor12, and is supplied to the earphone8for output to the user of the hearing device2.

An alternative embodiment of the hearing device2is illustrated inFIG.3, in which the analytical filter bank apparatus20and the synthetic filter bank apparatus40are each built with three stages. In addition to the first analytical filter bank22and the second analytical filter bank24, the analytical filter bank apparatus20in this embodiment includes a third analytical filter bank50that acts on a (first) subgroup52of the frequency bands30. The subgroup52in turn covers a low-frequency part of the sound spectrum that altogether extends over the frequency band30. For example, the subgroup52in particular includes—in the example according toFIG.3—the bottom two of the total of four frequency bands30; in the practical implementation, the subgroup52includes, for example, the bottom six of the total of 12 second frequency bands30.

Each second frequency band30of the subgroup52is split by the third analytical filter bank50in a second, yet finer, frequency splitting process into multiple (for example, into two, according toFIG.3) third frequency bands54(third frequency splitting process). The frequency bands54have a consistent (third) bandwidth of, for example, 62.5 Hz, and a consistent spectral spacing of 31.25 Hz.

A second subgroup56of the frequency bands30, which does not belong to the high-frequency frequency bands30belonging to the subgroup52, bypasses the third analytical filter bank50and is thus not subject to a third frequency splitting process.

In the embodiment of the hearing device2according toFIG.3, the subunit38of the signal processing unit34only processes the respective partial band signals of the high-frequency frequency bands30of the second subgroup56. For the processing, in particular the frequency-selective amplification, of the partial band signals of the frequency bands54, the signal processing unit34also includes, according toFIG.3, a further subunit58that is configured for the bandwidth of the frequency bands54.

The synthetic filter bank apparatus40is, also in the embodiment according toFIG.3, configured with mirror symmetry to the analytical filter bank apparatus20. In addition to the first synthetic filter bank44and the second synthetic filter bank42it therefore also includes a third synthetic filter bank60that combines the third frequency bands54back into the second frequency bands30of the subgroup52after the signal processing.

In the embodiment of the hearing device2according toFIG.3, predictor46only acts on the respective partial band signals of the high-frequency frequency bands30of the second subgroup56. In order to predict the partial band signals of the low-frequency second frequency bands30of the first subgroup52and of the third frequency bands54, the hearing device2according toFIG.3includes a further predictor62. The predictor62is preferably of the same type as the predictor46, but is configured in such a way that it compensates for the latency difference of the partial band signals of the high-frequency first frequency bands26of the subgroup32caused by the second and third frequency splitting processes.

The predictor62can also be disposed at different positions between the second analytical filter bank24and the second synthetic filter bank42. Furthermore, in variants of the embodiment according toFIG.3, multiple predictors62can also be connected in series, each of which compensates for a part of the latency difference. In a further variant embodiment, the predictors46and62are connected in series with one another. In this case the predictor46is disposed between the first analytical filter bank22and the second analytical filter bank24, or between the second synthetic filter bank42and the first synthetic filter bank44. In these cases, the predictor62is configured in such a way that it only compensates for the latency difference caused by the third frequency splitting process.

FIG.4shows a further embodiment of the hearing device2, which corresponds substantially to the embodiment according toFIG.2. In contrast to the embodiment according toFIG.2, the second frequency splitting process of the low-frequency first frequency bands26of the subgroup28however only takes place when the input audio signal I contains voiced speech (i.e. voice sounds that are spoken or sung).

A speech detection module64is implemented for this purpose in the signal processor12. The speech detection module64detects the presence of voiced speech by analyzing the input audio signal I that has been divided into the first frequency bands26, and in particular the low-frequency parts thereof. In the illustrated example, the frequency bands26of the subgroup28are supplied as the input variable to the speech detection module64. The speech detection module64detects the presence of voiced speech in this case, in particular through the presence of a marked fundamental frequency and/or the occurrence of characteristic dominant frequencies (formants) that are characteristic of voiced speech. When voiced speech is detected in the input audio signal I, the voice detection module outputs a control signal S1.

In order to only perform the second frequency splitting process when voiced speech has been detected, a signal switch66is connected in the signal path of the frequency bands26of the subgroup28, and passes the partial band signals of the frequency bands26of the subgroup28either to the second analytical filter bank24or to the subunit36of the data processing unit34depending on the control signal S1. When the control signal S1is applied (and thus when voiced speech has been detected in the input audio signal I) the signal switch66passes the partial band signals of the frequency bands26of the subgroup28to the second analytical filter bank24. In this case, the function of the hearing device2ofFIG.4corresponds to the embodiment illustrated inFIG.2. If, on the other hand, the control signal S1is not applied to the signal switch66(meaning that voiced speech is not detected in the input audio signal I by the speech detection module64), the signal switch66instead passes the partial band signals of the frequency bands26of the subgroup28directly to the subunit36of the data processing unit34. In this case the partial band signals of all the first frequency bands26are processed without any further frequency splitting process, and amplified, in particular in a frequency-specific manner. Prediction, again, does not occur in this case.

In an alternative variant embodiment of the hearing device2ofFIG.4, the second frequency splitting process is not activated depending on the detection of voiced speech, but depending on the accuracy (reliability) of the prediction. In this case the predictor46outputs a magnitude Q that is characteristic for the accuracy of the prediction, in particular in such a way that is known as the “predictor gain” which is given in decibels by the variance σx2of the input signal of the predictor46in relation to the variance of the prediction error σe2.

If—as shown inFIG.4—a plurality of partial band signals is supplied to the predictor, the characteristic magnitude Q is calculated from the mean value, the minimum value or the maximum value of the individual, band-specific, predictor gains. Alternatively, the predictor gain of a partial band signal chosen as a reference is employed as the characteristic magnitude Q. In all of these cases, the value of the characteristic magnitude Q becomes higher the more accurately the predictor46can predict the profile of the supplied partial band signals.

The characteristic magnitude Q is compared with a predefined threshold value is by an evaluation module68implemented in the signal processor12(and shown inFIG.4with a dashed line). As long as the characteristic magnitude Q remains above the threshold value, the evaluation module68outputs a control signal S2to that is supplied to the signal switch66instead of the control signal S1.

When the control signal S2is applied (and thus when the accuracy of the prediction is sufficient) the signal switch66passes the partial band signals of the frequency bands26of the subgroup28to the second analytical filter bank24. In this case, the function of the hearing device2ofFIG.4again corresponds to the embodiment illustrated inFIG.2. If, on the other hand, the control signal S2is not applied to the signal switch66(meaning that the prediction does not show sufficient accuracy), the signal switch66instead passes the partial band signals of the frequency bands26of the subgroup28directly to the subunit36of the data processing unit34for a predefined period of time. In this case the partial band signals of all the first frequency bands26are again processed without any further frequency splitting process, and amplified, in particular in a frequency-specific manner. Prediction, again, does not occur in this case. Once the predefined period of time has elapsed, the second frequency splitting process, and therefore also the prediction, is reactivated in order to check the accuracy of the prediction again by using the evaluation module68.

The speech detection module64is not provided in the variant embodiment described above. The signal switch66is, accordingly, only controlled by the control signal S2.

In a further variant embodiment of the hearing device2according toFIG.4, both the speech detection module64and the evaluation module68are provided. The signal switch66is operated in this case both by the control signal S1as well as by the control signal S2. The control signals S1and S2are preferably combined in this case with AND logic, so that the second frequency splitting process is only activated by the signal switch66when both the control signal S1and the control signal S2are present, in other words when the presence of voiced speech is detected in the input audio signal I, and when the prediction has sufficient accuracy.

In a further variant of the hearing device2according toFIG.4not shown in more detail, the characteristic magnitude Q is calculated separately for each frequency band26of the first subgroup28, in particular through a determination of the respective, band-specific prediction, and compared with a respective, band-specific, threshold value. The evaluation module68in this case outputs the control signal S2in a band-specific manner only for the frequency band26or the frequency bands26, for which the band-specific predictor gain exceeds the respectively assigned threshold value. The signal switch66accordingly activates the second frequency splitting process selectively only for the frequency band26or the frequency bands26concerned. In this variant of the hearing device, the predictor46is preferably disposed between the signal switch66and the second analytical filter bank24.

In a further variant of the hearing device2according toFIG.4, not illustrated in more detail, the control signal S1is generated in a band-specific manner if the presence of voiced speech is detected in the respective frequency band26by the speech detection module64. In this case again, the signal switch66accordingly activates the second frequency splitting process selectively only for the frequency band26or the frequency bands26concerned.

In a further variant of the hearing device2according toFIG.4, not illustrated in more detail, the predictor46is only switched out of the signal path connecting the microphone6the earpiece8when a value of the characteristic magnitude Q falls below the threshold value, but continues to run in the background of the signal processing (without the prediction in this case having any effect on the output audio signal O). This is, for example, achieved in that the signal switch66is connected, with mirror symmetry to the illustration according toFIG.4, between the second synthetic filter bank42and the first synthetic filter bank44. In this case, the predictor46also outputs the characteristic magnitude Q continuously when the characteristic magnitude Q does not exceed the threshold value. Switching back the signal switch after the predefined period of time has elapsed to check the accuracy of the prediction, as described for the exemplary embodiment according toFIG.4, is not necessary in this case, and is therefore also not provided.

The components of the signal processor12illustrated inFIGS.2to4, namely the analytical filter bank apparatus20with the analytical filter banks22,24and, if relevant,50, the data processing unit34with the subunits36,38and, if relevant,58, the synthetic filter bank apparatus40with the synthetic filter banks42,44and, if relevant,60, the predictor46and, if relevant, the predictor62, as well as, if relevant, the speech detection module64, the signal switch66and the evaluation module68are preferably implemented as software modules that run in the signal processor12when the hearing device2is operating. Alternatively, one or a plurality of these components are formed by non-programmable electronic circuits.

The invention is particularly clear in the exemplary embodiments described above, but is, however, not restricted to these exemplary embodiments. Rather can further embodiments of the invention be derived from the claims and the above description. In particular, the individual features of the invention described with reference to the exemplary embodiments in the context of the claims can also be combined in other ways without leaving the scope of the invention.

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