Patent Application
20090279724
This application claims priority of German application No. 10 2008 022 533.9 DE filed May 7, 2008, which is incorporated by reference herein in its entirety.
The invention relates to a method for operating a hearing device and a microphone system comprising at least two omnidirectional microphones emitting microphone signals.
Speech in noise-filled environments is a frequently known problem of hearing-impaired persons, which here require a signal-to-noise ratio of one to 10 dB in order to achieve the same speech intelligibility as persons with normal hearing. Moreover the natural directional effect of the outer ear is lost in the case of coverage using behind-the-ear hearing devices. The rehabilitation using hearing devices is thus not only to include the individual compensation of the hearing loss by means of amplification and dynamic compression but also the reduction of noises, in order to bring about a significant improvement in the speech intelligibility in noisy situations. Modern digital hearing devices exhibit noise suppression methods, which satisfy the hearing device-specific requirements in terms of efficiency, sound quality and artifact freedom.
Directional microphones in this way rank among noise suppression methods which were established several years ago and clearly lead to improvements in the speech intelligibility in auditory situations, in which the wanted signal and the interference signals come from different directions. In modern hearing devices, the directional effect is generated by differential processing of two or more adjacent microphones with omnidirectional characteristics. In “Störgerauschreduktion bei Hörsystemen der Gegenwart”, [Noise reduction in present day hearing systems] Chapter “Directional microphone systems”, 5th DGA Annual Convention 2002, differential 1st and 2nd order systems as well as systems with adaptive directional characteristics are described.
With the increasing development of hearing devices, the useable frequency range to be processed by hearing devices also increases. Shadowings and reflections of the acoustic waves on the head of the hearing device wearer cause the directional effect of known directional microphones to reduce significantly, so that acoustically wide-band interference signals, which are actually to be deleted by the directional microphone, are only suppressed in the lower frequency range. The interference signal as a result sounds very high-pass-like. This effect compromises the subjective perception of the hearing device wearer and/or the quality of the directional microphone.
The object of the invention is to overcome this disadvantage and to specify a method for operating a hearing device as well as microphone system, which offer a subjectively improved directional effect.
According to the invention, the set object is achieved with the method and the microphone system of the independent claims.
In accordance with the invention, a method for operating a hearing device comprising at least two omnidirectional microphones is specified. The microphones emit microphone signals and are electrically interconnected with one another in order to form a directional characteristic. A damping for the upper frequency range of the microphone signals is determined from the lower frequency range of the microphone signals. This is advantageous in that wideband interference signals are effectively damped.
In one development, the interconnected microphones can emit a signal with directional characteristics and the damping can be determined from a comparison of the signal with directional characteristics and the lower frequency range of a microphone signal. A directional effect is also achieved as a result in the case of high frequencies.
In a further embodiment, the upper frequency range of a microphone signal can be exposed to damping. Furthermore, the damped upper frequency range of a microphone signal can be added to the signal with directional characteristics. This gives the impression of a wideband directional microphone.
In a further embodiment, the upper frequency range of a combination of microphone signals can be exposed to the damping.
The damped upper frequency range of the combination of microphone signals can be advantageously added to the undamped signal with directional characteristics. In special ambient situations, this may result in improved results.
Furthermore, the upper frequency range of the signal with directional characteristics can be exposed to the damping and the damped upper frequency range of the signal with directional characteristics can be added to the undamped signal with directional characteristics.
The invention also specifies a microphone system for a hearing device comprising at least a first and a second omnidirectional microphone. The microphones emit microphone signals. The microphone system includes at least one first means, which separates the microphone signals into upper and lower frequency ranges, at least one second means, which forms a microphone signal with directional characteristics from the lower frequency ranges of the microphone signals, a third means, which determines a signal damping from a comparison of the lower frequency range of the microphone signal of the first microphone with the microphone signal comprising directional characteristics, and a fourth means, which damp the upper frequency range of the microphone signal of the first microphone with the determined signal damping.
In one development, the first means may include a crossover network, the second means a directional microphone unit, the third means a damping estimation module and/or the fourth means an adjustable damping element.
In a further embodiment, the microphone system may also include a fifth means, which adds the damped upper frequency range of the microphone signal of the first microphone and the microphone signal with directional characteristics.
The fifth means can preferably include an adder.
The invention also specifies a hearing device with an inventive microphone system.
Further details and advantages of the invention are apparent from the explanations which follow of several exemplary embodiments with reference to schematic drawings, in which;
A signal RA with directional characteristics leaves the directional microphone unit 7 and is fed into an input of a damping estimation unit 8. The lower frequency range RL1 of the first microphone signal R1 is fed to a further input of the damping estimation unit 8. A damping signal D is determined in the damping estimation unit 8 by comparing the signal RA with directional characteristics and the lower frequency range RL1 of the first microphone signal R1 with the aid of an estimation algorithm. A damping signal D leaves the estimation unit 8 at an output of the damping estimation unit 8 and is fed to an input of the controllable damping element 9.
According to the value of the damping signal D, the upper frequency range RH1 of the first microphone signal R1 is damped. The upper frequency range RHD of the first microphone signal R1 corresponding to the damping signal D leaves by way of an output of the damping element 9 and is fed to an input of a second adder 10. The signal RA with directional characteristics is fed to an additional input of a second adder 10. The two signals RHD, RH are added up in a second adder 10. A total signal HS leaves the second adder 10 by way of an output. The total signal HS is either fed directly to a receiver 11 or via a digital signal processing unit (not shown).
The inventive arrangement causes the wide-band frequency range which is recorded by the microphones to be separated into a lower and upper range. The differential directional microphone operates in the lower range, while the estimated damping is applied in the upper range. The estimated damping is estimated from a comparison of the omnidirectional signal and of the signal processed by the directional microphone and is possibly modified again. The estimated damping is applied in the upper frequency range in order to generate the impression of a wideband directional microphone.
As the majority of natural signals, such as speech or music, extend from the lower frequencies to the high frequencies, an estimation for the suppression of the signals existing there can be carried out in the lower frequency range by means of the directional microphone. The estimated damping, which is to take effect in the case of high frequencies, is directionally/omnidirectionally derived significantly from the performance ratio. In addition however, expert knowledge can also be introduced by way of a corresponding characteristic curve. The estimated damping is modified further in order to avoid artifacts.
As the high frequencies barely contribute to speech intelligibility and can also be poorly differentiated by a hearing device wearer, the subjective impression develops that the directional microphone would also operate in the high frequencies. This effect is particularly noticeable in the case of a pure wanted signal from the front and a pure interference signal from the rear. Here in the case of the wanted signal, the signal is reproduced at full volume and the pure interference signal is however damped across the whole frequency range.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 022 533.9 | May 2008 | DE | national |
