Patent Application
20120039496
This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2010 039 303.7, filed Aug. 13, 2010; the prior application is herewith incorporated by reference in its entirety.
The invention relates to a method for operating a hearing device, which is embodied for wireless signal transmission of a data signal at a transmission frequency, by providing an audio signal as a pulsed signal, in which a plurality of pulses fall within a predefined time slot, wherein the frequency spectrum of the audio signal has a notch into which the transmission frequency is placed. Moreover, the invention relates to a corresponding hearing device with a transmission apparatus for wireless signal transmission and a signal processing apparatus for processing pulsed signals. Here, a hearing device is understood to mean any sound-emitting equipment that can be worn in or on the ear, more particularly a hearing aid, a headset, earphones, or the like.
Hearing aids are portable hearing devices used to support the hard of hearing. In order to make concessions for the numerous individual requirements, different types of hearing aids are provided, e.g. behind-the-ear (BTE) hearing aids, hearing aids with an external receiver (receiver in the canal [RIC]) and in-the-ear (ITE) hearing aids, for example concha hearing aids or canal hearing aids (ITE, CIC) as well. The hearing aids listed in an exemplary fashion are worn on the concha or in the auditory canal. Furthermore, bone conduction hearing aids, implantable or vibrotactile hearing aids are also commercially available. In this case, the damaged sense of hearing is stimulated either mechanically or electrically.
In principle, the main components of hearing aids are an input transducer, an amplifier and an output transducer. In general, the input transducer is a sound receiver, e.g. a microphone, and/or an electromagnetic receiver, e.g. an induction coil. The output transducer is usually configured as an electroacoustic transducer, e.g. a miniaturized loudspeaker, or as an electromechanical transducer, e.g. a bone conduction receiver. The amplifier is usually integrated into a signal processing unit. This basic design is illustrated in
In digital hearing aids, the input signals to the receiver are digitally converted and often subjected to pulse density modulation. Alternatively, the audio signals to be processed can for example also be subjected to pulse width modulation or pulse code modulation. However, the examples in the following text always relate to pulse density modulation (PDM).
Modern, digital hearing aids often also contain a wireless communication system, by which data can be interchanged wirelessly with external equipment. The data transmission of these communication systems typically takes place within a narrow frequency band in the megahertz range. Compared to this, a pulse-density-modulated audio signal has a very broad spectrum. At the points of maximum pulse frequency in the audio signal, the spectrum has the typical notches.
As a result of the broad spectrum resulting from the pulse density modulation of the audio signal there is interference with the transmission frequency of the wireless communication system of the hearing aid. This means that, from the point of view of the transmission system, the PDM signal occurs as disturbance and hence has a detrimental effect on the signal-to-noise ratio (SNR). In end effect this leads to a higher symbol error rate.
Until now, the center frequency of the wireless transmission system was placed into a notch of the spectrum (zero in the amplitude spectrum) of the audio signal. Such notches in the spectrum of the audio signal are found at all multiples of the maximum pulse frequency of the pulse-density-modulated audio signal. In these regions the spectral energy of the PDM signal is very low within a narrow band range. Firstly, such a notch is very narrow and secondly images of the baseband audio signal occur in each notch. In order to keep the interference between the pulse-density-modulated audio signal and the high-frequency data signal of the wireless transmission system as low as possible, use is often made of electromagnetic shielding.
A traditional approach to reducing the signal power at relatively high frequencies consists of using an analog low-pass filter (LPF); however, this is absolutely inappropriate in hearing-aid technology. Due to the frequency of the wireless transmission system, which is in the low megahertz range, the reactive elements, by which the required time constants can be achieved, would not only be relatively large-volume but also very expensive. Moreover, the use of a low-pass filter would also reduce the efficiency of the entire apparatus, which in end effect leads to a reduced battery life. Moreover, the output impedance of the driver increases and becomes more frequency dependent.
It is accordingly an object of the invention to provide a method for reducing interference and a hearing device which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which increases the signal-to-noise ratio in a hearing device from the point of view of the wireless transmission system.
According to the invention, the object is achieved by a method for operating a hearing device, which is embodied for wireless signal transmission of a data signal at a transmission frequency. The method includes the steps of providing an audio signal as a pulsed signal, in which a plurality of pulses fall within a predefined time slot. A frequency spectrum of the audio signal has a notch into which the transmission frequency is placed, and the pulses of the audio signal within the predefined time slot are shifted such that the energy of the frequency spectrum drops in the vicinity of the transmission frequency.
Moreover, according to the invention provision is made for a hearing device with a transmission apparatus for wireless signal transmission of a data signal at a transmission frequency. The hearing device has a signal processing apparatus for providing an audio signal as a pulsed signal, in which a plurality of pulses fall within a predefined time slot. A frequency spectrum of the audio signal has a notch into which the transmission frequency is placed, and the signal processing apparatus can be used to shift the pulses of the audio signal within the predefined time slot such that the energy of the frequency spectrum is reduced in the vicinity of the transmission frequency compared to the un-shifted state. The transmission typically takes place within a frequency band that is usually arranged around a predefined carrier frequency or transmission frequency.
The reorganization of the pulses within a time slot advantageously influences the spectrum of the audio signal (the input signal of the receiver). Now, the pulses can be shifted such that the spectral energy of the audio signal reduces further in the vicinity of the notches, and so, in end effect, there are fewer disturbances by the pulsed audio signal from the point of view of the wireless transmission system and hence the signal-to-noise ratio is improved.
The audio signal is preferably provided as a pulse-density-modulated signal. However, additionally it can also be provided as, for example, a pulse-width-modulated signal or a pulse-code-modulated signal, or the like. In any case the audio signal then has corresponding pulses, which can be reorganized within a specific time slot.
In one advantageous embodiment, at least some of the pulses in the predefined time slot are contiguously shifted together to form a block. As a result of this shifting together there are peaks in the spectrum with increased energy outside of the notches, and so the signal energy drops in the vicinity of the notches.
In particular, at least some of the pulses in the predefined time slot can be shifted to an edge of the time slot. By way of example, the pulses can be shifted to the left edge of the time slot, i.e. at the beginning of the time slot, by simple measures.
Moreover, it is expedient if the predefined time slot has between three and ten pulses, preferably four or five pulses. This can “pull” the energy in the spectrum sufficiently far away from a notch.
As already indicated above, the present invention can be used particularly advantageously in digital equipment that has a wireless communication apparatus.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for reducing interference and a hearing device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
The audio signal to be processed is modulated in a hearing aid or another hearing device with the aid of e.g. pulse width modulation.
In the example in
If all pulses are now shifted to e.g. the left edge of a slot, and if there is a substantially uniform distribution (“pulse” (HIGH) on average occur as often as “no pulse” (LOW)), i.e. p(HIGH)=p(LOW)=0.5, the resultant, modified signal has rectangular properties. In the frequency domain, the modified PDM signal 14 leads to discrete lines 15 with the spacing of f r=f_A/w, which represents the rectangle with the shifted together pulses in the time domain. Here, f_A represents the maximum pulse frequency.
In the present example, the duration w of the slot is set to the variable 4, which means that there are w−1=3 equidistantly spaced lines 15 between two notches 17. The first discrete line next to the frequency or frequency band 2f_A of the wireless transmission system is at f_A (2+1/w).
As a result of the fact that the power is the same in both the unmodified signal and the modified signal, the concentration of the power in discrete lines 15 necessarily results in a reduction of power around these. Up to the first discrete line 15 at f_A (2+−1/w), the power of the modified signal is reduced by half (−3 dB) compared to the unmodified signal. This can be gathered even more clearly from
Increasing the SNR for wireless communication by reducing the power of the PDM signal around the discrete lines offers the chance of increasing the packing density of a hearing device or a hearing aid. As a result of the improved electromagnetic compatibility of the wireless transmission system with the internal signal processing equipment of the hearing device, the audio and RF components can be arranged closer together in the layout. Moreover, costs can be saved to the effect that expensive shielding can be dispensed with.
Now, the only question that remains unanswered is whether the modification of the PDM or audio signal changes the hearing impression of a user of the hearing device. This can be answered in the negative using the illustration in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 039 303.7 | Aug 2010 | DE | national |
