Electrical audio signal processing systems and devices – Hearing aids – electrical – Wideband gain control
Reexamination Certificate
1998-01-29
2001-03-06
Kuntz, Curtis A. (Department: 2743)
Electrical audio signal processing systems and devices
Hearing aids, electrical
Wideband gain control
C381S312000, C381S317000, C381S370000, C455S232100, C455S234200
Reexamination Certificate
active
06198830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for the amplification of input signals of a hearing aid, wherein a compression of the signals picked up by the hearing aid ensues dependent of the acquirable signal level. The present invention is also directed to a circuit for the implementation of the aforementioned method.
2. Description of the Prior Art
There is usually an impaired sensitivity to volume given a hearing disorder of the inner ear. Soft signals are usually not perceived and must therefore be correspondingly amplified in the hearing aid, but loud signals are heard just as loud as in the case of normal hearing. Compression circuits are employed in hearing aids in order to adapt the amplification of the signals to the auditory sensation of a person with normal hearing. Such compression circuits contain an AGC (Automatic Gain Control) circuit that varies the amplification dependent on the signal level. Such AGC circuits have either an exactly defined behavior or can be modified by parameter settings (for example, compression ratio, cut-in point of the compression, time constant). These settings are determined in the individual adjustment of the hearing aid to the hearing-impaired person and are usually not changed during use of the hearing aid. Known compression algorithms implement either a level-limiting compression or a “full dynamic range” compression. In the level-limiting compression, the cut-in point of the compression usually lies at a relatively high level, at which level the signals are significantly compressed (high compression ratio). As a result, loud signals are prevented from being too highly amplified. In “full dynamic range compression”, by contrast, the cut-in point of the compression usually lies as low as possible, with the compression ratio being selected such that the loudness sensed by the hearing-impaired person is balanced over the entire level range. An input-output characteristic that is based on stationary signals forms the basis for known techniques for calculating the parameter settings of a dynamics compression. Particularly in the employment of a loudness scaling, the sensed loudness is determined for stationary signals and the required compensation by the hearing aid is calculated therefrom. Given chronologically variable, modulated signals, i.e., speech, however, the time behavior of the compression circuit leads to an effectively different compression behavior. As a result the loudness perceived by the hearing-impaired person cannot be optimally compensated for all signals.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and circuit of the type initially described with which an optimum dynamics compression can also be achieved given chronologically variable, modulated signals.
This object is achieved in the inventive method and circuit by assuring a dynamics compression conducting, a signal analysis in addition to the acquisition of the signal level, and the behavior of the dynamics compression is varied on the basis of the result of the signal analysis.
The invention makes it possible to implement an optimum dynamics compression for all conceivable noise/auditory situations without having to switch between various parameter settings with a program switch. The variable dynamics compression ensues automatically dependent on the result of the signal analysis of the input signals. The invention assures a simpler manipulation of the hearing aid by the hearing-impaired person and a saving of switches as well as, further, an improvement of the speech comprehension. Given speech signals overlaid with unwanted noise, further, the subjectively perceived noisiness can be reduced. The satisfaction of the hearing aid wearers can be significantly increased as a result and the length of time the hearing aids are worn can be effectively lengthened.
The signal analysis preferably ensues as a modulation frequency analysis of the input signal. The time variation of the envelope of the input signal is thereby spectrally analyzed.
The variation of the dynamics compression on the basis of the result of the signal analysis can ensue in various ways. The variation of the dynamics compression can be accomplished by modifying the time constant in the acquisition of the level of the input signal, i.e. the time constant in the level detector, or by variation of the compression ratio of the amplification element, particularly AGC amplification element.
Both of the above possibilities for variation can be simultaneously utilized. For example, long time constants and/or high compression ratios can be utilized given low modulation frequencies, for example given slowly varying signals. When high modulation frequencies occur, for example given rapidly varying signals, by contrast short time constants and/or smaller compression ratios can be employed. Other combinations of time constants and compression ratios can be applied.
Moreover, the cut-in point of the compression after the signal analysis has ensued can be utilized for the variation of the dynamics compression.
According to a further embodiment of the present invention, the input signals are resolved into a number N of frequency bands and individual signal analyses are undertaken referenced to each frequency band. Subsequently, the frequency bands are merged after the amplification. As a result, the entire frequency spectrum can be sampled and optimally edited for the dynamics compression.
There is also the possibility of selectively amplifying certain frequency bands, or signal frequencies occurring therein, in a “customized” manner. There is also the possibility of combining individual frequency bands for the signal analysis and/or for the implementation of the dynamics compression. Alternatively, the signal analysis can be limited to one frequency band, with the control of the AGC parameters in all frequency bands ensuing on the basis of this signal analysis.
The invention also allows a suppression of unwanted noise to be undertaken by implementing a partial band analysis in a number of frequency bands, with the modulation analysis being undertaken in each channel. The suppression of unwanted noise occurs by attenuating the signal in those channels in which the modulation analysis detects a high noise component.
A filter band analysis or filter band synthesis is preferably employed for the resolution of the input signals as well as for the merging of the frequency bands after the amplification. Instead, a Fourier analysis or wavelet analysis can be implemented.
Instead of the modulation frequency analysis, some other signal analysis that can likewise be employed for the adaptive variation of the dynamics compression can be used such as, for example, a cepstral analysis or a short-term spectral analysis (time-frequency analysis). The time-frequency patterns acquired with the last-cited short-term spectral analysis can be employed for the classification of the acoustic signals.
In addition to the adaptive modification of the parameters of the AGC circuit on the basis of the signal analysis, a manual variation of the parameters by the hearing aid wearer can also inventively ensue with values being changed over a continuous range or in steps.
The invention is particularly suited for the use of digital signal processing, however, it can also be realized in the framework of analog signal processing.
The inventive circuit includes a signal analysis module that is connected to the input signal path and to a level detector and/or to an AGC amplification element.
In view of the signal analysis that is undertaken, the signal analysis module—for varying the dynamics compression—effects a variation of the time constant in the level detector or a modification of the gain characteristic of the AGC amplification element, ideally a modification of both values.
A delay element can be arranged in the input signal path for the compensation of signal transit times in the calculation of the gain value.
REFERENCES:
patent: 3993862 (1976-1
Hohmann Volker
Holube Inga
Kollmeier Birger
Harvey Dionne
Kuntz Curtis A.
Schiff & Hardin & Waite
Siemens Audiologische Technik GmbH
LandOfFree
Method and circuit for the amplification of input signals of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and circuit for the amplification of input signals of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and circuit for the amplification of input signals of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2453068