Hearing aid and method for signal processing in a hearing aid

Abstract

The hearing aid (2) has an input transducer (4), a signal processing unit (6), and an output transducer (8), wherein the signal processing unit (6) has a filter bank (14) for dividing an input signal (E, E') into a plurality of signal components (Sf) in different frequency bands, a processing unit (12) for processing the signal components (Sf), and a synthesis unit (18) for synthesizing the processed signal components (Sf) to form an output signal (A, A'). To limit the level of an output signal (A), a level detector (20) is arranged upstream of the synthesis unit (18), which is designed to determine a signal level (P) based on the signal components (Sf) and to output a level signal (Sp). A level limiter (24), to which the level signal (Sp) is transmitted, is arranged downstream of the synthesis unit (18) and is designed to limit the level of the output signal (A) as a function of the level signal (Sp).

Description

[0001] The invention relates to a hearing aid with an input transducer, a signal processing unit, and an output transducer. The signal processing unit comprises a filter bank for dividing an input signal into signal components in several different frequency bands, a processing unit for processing the signal components, and a synthesis unit for synthesizing the processed signal components into an output signal. The invention further relates to such a signal processing method.

[0002] Such a hearing aid and method can be found in EP 2 389 773 B1. This prior art, as well as the present invention, address the problem that, at high input signal levels, i.e., with loud sound sources, the signal processing in the hearing aid can result in an excessively high signal level being output at the end of the signal processing, so that the signal output to the user is perceived as unpleasant. High signal levels also lead to high energy consumption and high current peaks when the electrical signal is converted into an acoustic signal for the user. This, in turn, can impair the power supply and, for example, lead to voltage dips, which can cause the hearing aid to malfunction.

[0003] According to EP 2 389 773 B1, the signal level of an electrical input signal is determined before the input signal is fed to a filter bank and divided there into different signal components in different frequency bands (frequency channels). Specifically, temporary loud noises, so-called transients, within the input signal are detected. Depending on whether transients are detected, a calculation and, if necessary, an adjustment of an amplification factor is performed in the individual frequency bands (frequency channels). The various signal components of the various channels are then combined in a summing unit and provided as an electrical output signal, which is then converted into an acoustic output signal in an output transducer.

[0004] Based on this, the invention is based on the object of providing improved signal limitation for loud input signals, in particular in the presence of the aforementioned transients.

[0005] The object is achieved according to the invention by a hearing aid with an input transducer, a signal processing unit, and an output transducer. The signal processing unit has a filter bank for dividing an input signal into multiple signal components in different frequency bands and thus into different channels, a processing unit for processing the signal components, and a synthesis unit for synthesizing the processed signal components into an output signal. The output signal is then transmitted at least indirectly to the output transducer. The signal processing unit further has a level detector, which is designed to determine a signal level based on the signal components and to output a level signal. The level detector is arranged upstream of the synthesis unit.Furthermore, a level limiter is provided to which the level signal is transmitted and which is designed to limit the level of the output signal depending on the level signal.

[0006] The invention is further achieved by a method for signal processing, in particular in such a hearing aid, in which an input signal is divided into several signal parts in different frequency bands, the signal parts are processed, the processed signal parts are combined to form an output signal, a signal level is determined on the basis of the signal parts and a level signal is generated based on this, a level of the output signal is limited on the basis of the level signal.

[0007] It's important to note that the signal level is determined based on the signal components and thus only after the filter bank. This measure makes it possible to determine the signal level and thus whether signal limiting is necessary only after at least some signal processing steps have already been completed, allowing a more precise determination and assessment of whether the output signal level is too high.

[0008] It's also worth emphasizing that the level limiter is located downstream of the synthesis unit and affects the output signal composed of the processed signal components. The signal limiting is therefore broadband, meaning it affects the combined output signal and not just individual frequency bands. This prevents signal distortion due to different frequency-specific and thus channel-specific gain factors.

[0009] The level limiter is positioned downstream of the signal processing path and thus offset from the level detector in signal processing. Considering that a certain processing time is required for level detection, this ensures that level limiting occurs in a timely manner. The inherent delay in the (further) signal processing between the level detector and the level limiter is therefore appropriately exploited to reliably apply level limiting when the high level is present. Overall, this decouples level determination from level limiting in terms of time.

[0010] The signal processing unit is, in particular, a digital signal processing unit specifically designed as a digital signal processor. In this context, a filter bank is generally understood to be a processing unit that divides the electrical input signal supplied to the signal processing unit into several frequency bands and thus into several frequency channels. A signal component is analyzed and processed in each channel before the various signal components are reassembled.

[0011] The processing unit for processing the signal components therefore has a channel-specific processing unit for each frequency band, and thus for each frequency channel. Each of these channel-specific processing units typically has several channel-specific signal processing components, such as channel-specific filters or channel-specific amplifier components.

[0012] The filter bank typically transforms the input signal from the time domain to the frequency domain. Signal processing within the processing unit, and thus the processing of the signal components, therefore takes place in the frequency domain.

[0013] In general, the (electrical) input signal is initially provided to the signal processing unit in the time domain, which is then transformed into the frequency domain by the filter bank. Finally, the synthesis unit converts the signal from the frequency domain to the time domain. Therefore, the output signal is provided in the time domain following the synthesis unit.

[0014] By arranging the level detector before the synthesis unit and the level limiter after the synthesis unit, the fact that a certain processing time (delay) is required for the transformation from the frequency domain to the time domain is exploited, which is used for the level determination and especially to ensure that the level limitation takes place reliably at the desired time.

[0015] In a preferred embodiment, the level detector is arranged downstream of at least one signal processing section of the processing unit. This ensures that at least one and preferably several signal processing steps have already been performed within the processing unit, and thus in particular within the frequency domain processing, before the level determination is performed.

[0016] In a preferred embodiment, one of these signal processing parts is a (channel-specific) amplifier part and the level determination only takes place downstream of such a channel-specific amplifier part.

[0017] Overall, this ensures that the signal level is determined on the basis of previously processed signal components, so that the most reliable estimation and determination possible can be made as to whether the output signal is expected to be too high.

[0018] Preferably, the level detector is arranged directly upstream of the synthesis unit. The level detector is thus arranged downstream of the complete signal processing of the signal components. The level detector is therefore arranged downstream of the final signal processing component of the processing unit.

[0019] In a preferred embodiment, the level limiter is arranged downstream of an output processing unit designed to process the output signal output by the synthesis unit. This output processing unit is generally a signal processing unit downstream of the synthesis unit, which therefore performs, in particular, signal processing of the already composed electrical output signal. Within the scope of this output signal processing unit, for example, filtering and / or scaling of the signal in the time domain takes place.

[0020] In a preferred embodiment, the level detector and the level limiter are directly connected to each other, so that during operation the level signal is transmitted directly from the level detector to the level limiter. Direct connection or direct transmission means that no additional processing units for signal processing are installed on the signal path for the level signal; in particular, the direct and immediate connection eliminates any signal delay. The level detector is therefore directly connected to the level limiter via a direct, simple signal line, for example, a printed circuit board. This ensures the fastest possible signal transmission to the level limiter.

[0021] In a preferred embodiment, an input signal processing unit is further arranged upstream of the filter bank, which is designed to process the input signal upstream of the filter bank. In particular, an initial signal processing is performed in the time domain before the division into the various frequency bands is performed. Within the scope of this input signal processing unit, for example, filtering and / or scaling in the time domain takes place.

[0022] Preferably, therefore, supplementary signal processing steps for the respective overall signal in the time domain are carried out both on the input side and on the output side of the processing unit and thus before and after the signal processing in the frequency domain.

[0023] Preferably, the level detector and the level limiter are configured such that the level signal correlates with the signal level and such that, particularly after a threshold value for the signal level is exceeded, the level of the output signal is increasingly limited as the signal level increases. In this case, the level signal therefore also contains information about the level of the signal level determined by the level detector. In particular, continuous adjustment of the limit is provided, or alternatively, adjustment of the limit in discrete steps.

[0024] According to an alternative embodiment, for example, once a limit value for the signal level is exceeded, a fixed, predetermined limit, specifically a fixed limiting factor, is set.

[0025] Determining a signal level based on channel-specific signal components in the frequency domain is generally known. Typically, the individual signal components in the various channels are analyzed and evaluated. Specifically, for example, a channel-specific signal level is determined for each channel and checked for exceedance of a specific channel-specific limit. The level detector, for example, has a channel-specific level detector for each channel.

[0026] For example, a level signal to limit the level of the output signal is output when the channel-specific limit value is exceeded in a channel.

[0027] In a preferred embodiment, the level detector is designed to estimate a broadband signal level based on the signal components. This means that a common, expected signal level is determined based on several, and in particular all, signal components, which is present in the composite output signal after the synthesis unit and before the level limiter, and especially before the output signal processing unit.

[0028] An exemplary embodiment of the invention is explained in more detail below with reference to the single figure. This figure shows, using a simplified block diagram, an example of signal processing in a hearing aid.

[0029] A hearing aid 2 shown in the figure is designed, in particular, as a hearing aid device that is designed and configured to compensate for user-specific hearing impairments. Such a hearing aid 2 is adapted to the user-specific hearing impairments of a specific user through an adaptation process, for example, by a hearing aid acoustician. For this purpose, the values of various setting parameters are appropriately adjusted.

[0030] The hearing aid 2 generally comprises an input transducer 4, a digital signal processing unit 6, and an output transducer 8. An electrical, digital input signal E is generally provided via the input transducer 4 at the input of the signal processing unit 6. This digital input signal E is processed by the signal processing unit 6 and made available at the output of the signal processing unit 6 as a digital output signal A and transmitted to the output transducer 8.

[0031] Input transducer 4 and / or output transducer 8 are typically, but not necessarily, electroacoustic transducers that convert an acoustic signal into an electrical signal and vice versa. Specifically, input transducer 4 is a microphone, and output transducer 8 is a receiver / speaker.

[0032] In the illustrated embodiment, the input signal E is first subjected to a first signal processing step in an input processing unit 10. This first signal processing step occurs in the time domain.

[0033] A processing unit 12 is arranged downstream, in which signal processing takes place in the frequency domain. For this purpose, the processing unit 12 has a filter bank 14 on the input side, which divides the input signal E, in particular the processed input signal E' provided by the input processing unit 10, into several signal parts Sf in different frequency bands or frequency channels. A respective frequency channel is in the Figure 1 represented by a respective line within the processing unit 12. Within the processing unit 12, therefore, a frequency-specific or channel-specific processing of the input signal E, E' in the frequency domain takes place.

[0034] The processing unit 12 itself, in turn, has several signal processing sections 16 that apply various signal processing functions to the signal. In particular, one of these signal processing sections 16 is designed as an amplifier section. Each signal processing section 16 is typically divided into channel-specific signal processing sections, preferably identical to one another.

[0035] Following the processing unit 12, a synthesis unit 18 is arranged, in which the various signal components Sf are recombined to form a common output signal A, A`. The output signal emitted by the synthesis unit is designated by the reference symbol A`.

[0036] The processing unit 12 further comprises a level detector 20, which is designed to determine a particularly broadband signal level P. Based on the signal level P determined by the level detector 20, the latter outputs a level signal Sp.

[0037] In the exemplary embodiment, the output signal A` output by the synthesis unit 18 is transmitted to an output processing unit 22, in which further signal processing takes place, now again in the time domain.

[0038] In the FIGURE, three dashed areas I, II, III are shown within the signal processing unit, with the input-side area I and the output-side area III marking the signal processing in the time domain and the area II arranged in between marking the signal processing in the frequency domain.

[0039] A level limiter 24 is arranged downstream of the output processing unit 22. This is, in particular, part of a power amplifier not shown in detail here. The level signal Sp is transmitted directly from the level detector 20 to the level limiter 24. The level limiter 24 limits the level of the output signal A provided at the output of the signal processing unit 6 and transmitted to the output converter 8, if necessary.

[0040] The output signal A is then converted by the output converter 8, in particular a loudspeaker, preferably into an acoustic output signal and presented to the user.

[0041] The level detector 20 determines a broadband signal level P on the basis of several of the signal parts Sf, in particular on the basis of all signal parts Sf. This is generally a measure of an expected signal level in the output signal A' output by the processing unit 12 at its output.

[0042] To determine the signal level P, channel-specific signal levels of the individual signal components SF are determined and fused to form the signal level P.

[0043] The broadband signal level in the frequency domain is generated primarily by summing the linear signal powers (partial powers) of all frequency bands (squared magnitudes of the signal components Sf). Preferably, a correction factor is applied to each partial power at the output of the filter bank, preferably with a constant band overlap between the subbands. After summation, the broadband level is determined, for example, by taking the logarithm of the total linear signal power. This procedure is also known in the technical literature as a "modified periodogram."

[0044] If the signal level P determined in this way is above a predetermined, possibly user-specific limit value, the level signal Sp is sent to the level limiter 24 as an indication that the limit value has been exceeded.

[0045] In particular, the level signal Sp correlates with the determined signal level P, i.e., it contains information about the actual level of the determined signal level P. The limitation performed by the level limiter 24 when the limit value is exceeded correlates with the signal level P, i.e., the limitation increases continuously with increasing signal level P.

[0046] Overall, this achieves a suitable, reliable and fast limitation of the level of the output signal A in the case of transients or generally a high input level. List of reference symbols

[0047] 2 Hearing aid 4 Input converter 6 Signal processing unit 8 Output converter 10 Input processing unit 12 Processing unit 14 Filter bank 16 Signal processing section 18 Synthesis unit 20 Level detector 22 Output processing unit 24 Level limiter EInput signal E'Input signal at the input of the processing unit 12 AOutput signal A'Output signal at the output of the processing unit 12 SfSignal part SpLevel signal I, IIISignal processing in the time domain IISignal processing in the frequency domain

Claims

1. Hearing aid (2) with an input transducer (4), a signal processing unit (6) and an output transducer (8), wherein the signal processing unit (6) has a filter bank (14) for dividing an input signal (E, E') into several signal parts (Sf) in different frequency bands, a processing unit (12) for processing the signal parts (Sf) and a synthesis unit (18) for synthesizing the processed signal parts (Sf) to an output signal (A, A'), characterized in that a level detector (20) is arranged upstream of the synthesis unit (18), which is designed to determine a signal level (P) on the basis of the signal parts (Sf) and to output a level signal (Sp), and furthermore a level limiter (24) is arranged downstream of the synthesis unit (18), to which level signal (Sp) is transmitted and which is designed to limit the level of the output signal (A) as a function of the level signal (Sp).

2. Hearing aid (2) according to the preceding claim, characterized in that the level detector (20) is arranged downstream of at least one signal processing part (16) of the processing unit (12).

3. Hearing aid (2) according to the preceding claim, characterized in that the level detector (20) is arranged immediately before the synthesis unit (18).

4. Hearing aid (2) according to one of the preceding claims, characterized in that the level limiter (24) is arranged downstream of an output processing unit (22) which is designed to process the output signal (A') provided by the synthesis unit (18).

5. Hearing aid (2) according to one of the preceding claims, characterized in that the level detector (20) and the level limiter (24) are directly connected to each other for the immediate transmission of the level signal (Sp).

6. Hearing aid (2) according to one of the preceding claims, characterized in thatan input processing unit (10) is arranged in front of the filter bank (14), which is designed to process the input signal (E) in front of the filter bank (14).

7. Hearing aid (2) according to one of the preceding claims, characterized in that the level detector (20) and the level limiter (24) are designed such that the level signal (Sp) correlates to the signal level (P), and that with increasing signal level (P) an increasing limitation of the level of the output signal (A) takes place.

8. Hearing aid (2) according to one of the preceding claims, characterized in that the level detector (20) is designed to estimate a broadband signal level (P) on the basis of the signal parts (Sf).

9. Method for signal processing in a hearing aid (2), in particular according to one of the preceding claims, in which - an input signal (E, E') is divided into several signal parts (Sf) in different frequency bands, - the signal parts (Sf) are processed, - the processed signal parts (Sf) are combined to form an output signal (A, A'), characterized in that - a signal level (P) is determined on the basis of the signal parts (Sf) and a level signal (Sp) is generated based thereon, - a level of the output signal (A) is limited on the basis of the level signal (Sp).

10. Method according to the preceding claim, in which the determination of the signal level (P) takes place immediately before the combination of the signal parts (Sf).

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