EP1135968B1 - Method for producing a constant sound pressure level in hearing aids and corresponding hearing aid - Google Patents

Description

The invention relates to a hearing aid with the features of The preamble of claim 1 also relates to the invention a method for operating a hearing aid with the Features of the preamble of claim 7.

Hearing aids often have the task of being adjustable No uncomfortable threshold for signal amplification to exceed and thus generate constant sound pressure levels. This can be done with a signal amplitude control feedback structure can be achieved, whereby the (reinforced) Input signal is given to a level detector and its output value in a control loop with an attenuation of the output signal with increasing input signal strength is entered.

If there is a high gain within the control loop Phase shifts of approximately 180 ° so that instead the desired negative feedback is an undesirable positive feedback occurs.

From WO 97/28600 a "compander", i.e. Compressor / expander circuit, for use in a battery powered Device known. The device includes an input to Recording an analog input signal, signal processing means to generate a digital signal, which with the Envelope of the input signal corresponds, and means to link the digitized envelope with the analog one Input signal to an analog output signal ready to deliver. When compressing the analog input signal the output signal is proportional to the product of the input signal and the reciprocal of the envelope. When expanding of the analog input signal is the output signal proportional to the product of the input signal and the envelope.

From US 5,724,433 a circuit for automatic Gain control in a hearing aid known. The circuit includes an adaptive compression and filter circuit with a variety of channels with a common output are connected. The amplification of a channel is dependent of the output signal and a discomfort threshold for the channel in question. The gain setting of the channel concerned is increased as long as the output signal of the channel below a preset one Threshold lies and reduces as long as the output signal is above the threshold lies.

In a further embodiment, hearing aids are used in State of the art for generating constant sound pressure levels uses a forward structure with gain table. This has the disadvantage that the gain table with the stored gain values with greater gain grows disproportionately. In addition, in the transition area discrepancies between two stored gain values occur, which leads to an increased distortion factor of the signal being able to lead.

The invention has for its object a hearing aid and to offer a method for operating a hearing aid in which the sound pressure level at the output is adjustable Do not exceed discomfort threshold.

The task is for the hearing aid with the characteristics of the characteristic Part of claim 1 in conjunction with the Features of the generic term solved. Advantageous embodiments of the hearing aid are described in claims 2-6. For the procedure, the task is characterized by the characteristics of the characterizing part of claim 7 in conjunction solved with the features of the generic term. Further Process variants are described in claims 8-12.

The basic idea of the invention is to provide signal values Signals, the envelope values of which are adjustable Exceed the threshold value due to the envelope values to divide. This creates a signal with constant Envelope. This signal is sent to the hearing aid speaker output, the resulting signal has a constant SPL.

The invention is characterized in that at one Hearing aid the sound pressure level at the output an adjustable Threshold does not exceed and over a large one Fluctuation range of the sound pressure level at the entrance and / or a large gain range is kept constant, and this with little effort and with little if any Signal distortion.

In the hearing aid according to the invention, the envelope of the processing and to be limited in the sound pressure level Signals determined in an envelope generator. In one Dividers become quotients from the signal values of the processing signal and the associated envelope values determined. The signal values are thus at the output of the Dividieres in a limited range, for example in the range between -1 and +1. Because of the limited Rise time of realizable envelope generators can be in in practice it happens that signal values are briefly outside of the area enclosed by the envelope. According to one embodiment of the invention, such Signal values recorded and also in the limited Range of values shown. For example, each signal value outside the area enclosed by the envelope assigned a constant value. That from the individual Output signal values has composite output signal over a certain amplification range of the hearing aid essentially constant envelope.

The hearing aid according to the invention has, in particular, a digital one Signal processing with a DSP element. The Circuit expenditure of the hearing aid according to the invention in one advantageous embodiment by recognizing the sign the signal and envelope values to be processed be reduced so that only positive values are processed and negative values are inverted. This can be used as a divider a 1 quadrant divider can be used consists of a simple shift-subtract unit.

In order to reduce the risk of clipping, before the quotient formation the signal value of the signal to be processed reduced by an adjustable correction element.

The determined element is advantageously used in a comparison element Envelope value compared to a gain value. The latter can be the reciprocal of the greatest possible gain in the hearing aid. Now if the envelope value is the adjustable gain value falls below, means this means that the signal to be processed is below the set Discomfort threshold is and it becomes the gain parameter instead of the envelope value for further processing used, causing hypersensitivity to signal processing of the hearing aid is avoided.

In an advantageous embodiment, the signal value and the envelope value determined in a comparison element compared with each other to avoid that the value of the Quotients of signal value and envelope value the representable Number range from "-1" to "+1" exceeds.

If the quotient of the signal and envelope value from the amount forth exceeds the value "1", is via a switching element instead of the quotient determined, a fixed output value as Signal to be output determines what the predetermined Numerical range from "-1" to "+1" is observed.

In the method according to the invention, constant sound pressure levels generated by the quotient of the signal value and the envelope value of the signal value is formed. The output signal composed of the individual quotient values is limited in its sound pressure level and exhibits an essentially constant envelope.

In a variant of the method according to the invention, the Signal value to be output or processed the value the quotient of the signal value and the envelope value, if the Envelope value exceeds the signal value. It can be used in one digital signal processing the representable number range from "-1" to "+1" are adhered to.

If now the quotient of the signal value and the envelope value is the representable range of numbers, e.g. the amount exceeds the value "1", not the quotient, but a specifiable fixed output value within the representable Number range used as the signal value to be output.

Other process variants have already been linked explained with the hearing aid according to the invention or are based on of the embodiment shown.

The drawing figure shows a basic circuit diagram of the invention Hearing aid. Generally is under the term "Hearing aid" both a separate ITE or a BTE device like also an implantable hearing aid, generally a hearing aid to understand.

The basic circuit diagram shows core elements of the invention Hearing aid shown, further elements such as A / D and D / A converter are not shown.

The hearing aid has a microphone 1, a signal processing unit 2 and a speaker 13. The one to be processed Starting from microphone 1, the signal passes through a circuit unit 16, the above a certain input sound pressure level provides an output signal with a constant envelope. The level-limited output signal of the circuit unit 16 is then in the signal unit 12, which e.g. as a DSP element is executed, processed and the speaker 13 fed.

The value range of the signal to be processed lies in Embodiment between -1 and +1. When entering the Circuit unit 16 is the detector element 3 Sign of a signal value to be processed determined. If this is negative, there is one in the switching element 4 Sign inversion instead, otherwise it runs through processing signal value the switching element 4 without Inversion.

In the correction element 5, the value of the to be processed can Signals to avoid clipping with an adjustable Factor must be multiplied. For example, the factor ½ causes the reduction in the sound pressure level of the signal 6 dB. In addition, this factor can also be used for adjustment serve the discomfort threshold. In the invention Hearing aid first becomes a signal value of the one to be processed Signals in an envelope generator an envelope value determined. This comes with an adjustable gain characteristic 14 compared in the comparative element 7. As an output signal of the comparison element becomes the envelope value switched on when it reaches the gain characteristic 14 or exceeds.

If the gain characteristic value 14 is undershot, it is detected that that the envelope value is below the set one Inconvenience threshold and it is instead of the Envelope value the gain characteristic 14, which e.g. the Reciprocal of the greatest possible amplification of the hearing aid corresponds as the output signal of the comparison element 7 passed.

In the comparison element 9, the signal value and the output value of the comparison element 7 compared while in the divider 8, which advantageously as a 1-quadrant divider the quotient of the signal value and the output value of the comparison element 7 is determined.

If as a result of the comparison of values in the comparative element 9 it is determined that the baseline of the predicate 7 exceeds the signal value, the quotient is the result the division of the signal value and the output value of the comparison element 7 in the divider 8 via the switching element 10 passed on as its output signal.

However, if the signal value is the output value of the comparison element 7 and this by means of the comparative element 9 is determined, instead of the quotient of the signal value and output value of the comparison element 7 an adjustable Fixed output value 15 in the switching element 10 as its output signal advanced.

The fixed output value 15 exceeds the representable number range e.g. from "-1" to "+1" not and can therefore in the signal unit 12 can be processed further.

In general, the switching element 10 has a relay function and serves as a 1 out of 2 multiplexer.

If the signal value of the negative in the circuit unit 16 Half wave of a signal is processed, the positive Sign of the signal to be output after the switching element 10 after detection by the detector element 3 the switching element 11 can be inverted into a negative signal. Otherwise the output signal of the switching element passes through 10 the switching element 11 without sign correction Further processing in the signal unit 12.

According to the invention, a level-limited output signal is produced after the signal processing described in the circuit unit 16 for further processing in the signal unit 12.

The signal to be processed is in the exemplary embodiment it is the digital acoustic output signal of a Microphone. The value range of this signal is between -1 and +1. The invention is not in this range of values limited. After a corresponding adjustment of the circuit signals with any value range after the same principle can be processed. The signal can also appear the circuit unit for generating constant sound pressure levels a signal preprocessing unit (not shown) run through. This can be filtering or, for example Include reinforcement.

Claims (12)

1. Hearing aid comprising a microphone, a receiver and a signal processing unit with a circuit for producing constant sound pressure levels, whereby the circuit (16) has an envelope generator (6) for producing an envelope value of a signal value to be processed and a divider (8) for calculating the ratio of the signal value and the calculated envelope value as a signal to be output or further processed, characterised in that a comparator element (7) is provided for comparing the envelope value of the envelope generator (6) with a gain parameter (14), whereby further processing of the signal to be processed takes place as a function of the gain parameter if the envelope value falls below the gain parameter, and further processing of the signal to be processed takes place as a function of the envelope value if this envelope value reaches or exceeds the gain parameter.
2. Hearing aid according to Claim 1, characterised in that the divider (8) is a 1-quadrant divider.
3. Hearing aid according to Claims 1 or 2, characterised in that a corrector element (5) is provided for reducing the signal value of the signal to be processed in order to prevent clipping.
4. Hearing aid according to one of Claims 1 to 3, characterised in that the gain parameter can be adjusted.
5. Hearing aid according to one of Claims 1 to 4, characterised in that a comparator element (9) is provided for comparing the signal value with the calculated envelope value.
6. Hearing aid according to one of Claims 1 to 5, characterised in that a switch element (10) is provided for switching an output fixed value (15) or the output value of the divider (8) as a signal to be output by the circuit (16).
7. Method for operating a hearing aid comprising a microphone, a receiver and a signal processing unit with a circuit for producing constant sound pressure levels, in particular for operating a hearing aid according to one of Claims 1 to 6, characterised in that the envelope value is compared with a gain parameter and the signal to be processed is further processed as a function of the envelope value if the gain parameter is reached or exceeded and otherwise the signal to be processed is further processed as a function of the gain parameter.
8. Method according to Claim 7, characterised in that the ratio of the signal value and the envelope value of the signal value is calculated as a signal value to be output or further processed.
9. Method according to Claims 7 or 8, characterised in that the signal value is reduced, e.g. halved, before taking the ratio with the envelope value, in order to prevent the risk of clipping.
10. Method according to one of Claims 7 to 9, characterised in that a negative sign of the signal value is detected and inverted.
11. Method according to one of Claims 7 to 10, characterised in that the signal value to be output corresponds to the value of the ratio of the signal value and the envelope value if the envelope value exceeds the signal value.
12. Method according to one of Claims 7 to 11, characterised in that the signal value to be output corresponds to a predeterminable output fixed value if the envelope value corresponds to the signal value or falls below the latter.

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