The invention shall now be described by examples and with the help of figures. They show:
FIG. 1 by means of a simplified signal flow/functional block diagram the method according to the present invention performed for beam-forming processing an input audio signal which is generated by an input acoustical-to-electrical converter arrangement;
FIG. 2 the processing according to FIG. 1 under a more generalized aspect;
FIG. 3 in a representation in analogy to that of FIG. 1, processing of the output signal of an acoustical-to-electrical converter arrangement in the two domains specifically for mismatch compensation, and
FIG. 4 under a more generalized aspect, the processing as realized by the embodiment of FIG. 3.
In FIG. 1 there is shown by means of a simplified functional block/signal flow diagram a specific embodiment according to the present invention, wherein signal processing is beam-forming at a or for a hearing device. There is provided an input acoustical-to-electrical converter arrangement 1, which, generically, generates an output electric audio signal Sin, input signal for subsequent processing. This signal is dependent from acoustical signals impinging on a converter array of the at least two converters 1a and 1b of the arrangement 1.
In the embodiment of FIG. 1 the output audio signal Sin of the acoustical-to-electrical converter arrangement 1, consisting of two electric signal Sa and Sb according to the two specific converters 1a and 1b, is separated into two parts Sin1 and Sin2. Specifically the two parts Sin1 and Sin2 are formed by the higher-frequency components and of the lower-frequency components respectively of both signals Sa and Sb. Thus, the output signal of converter 1 with the two components Sa and Sb is separated by respective highpass and lowpass filters HPa, HPb and LPa, LPb, into the two parts of higher-frequency content and of lower-frequency content. The second part Sin2 of the output signal of converter 1, consisting of the low-frequency components as filtered by the lowpass filters LPa and LPb, is fed specifically as the signals SLPa and SLPb to a beam-forming unit 3, wherein, in time-domain processing P, beam-forming is performed upon the signals SLPa and SLPb. As exemplified this is done by means of the delay-and-add technique which is perfectly known to the skilled artisan. By means of allpass filter units 5a and 5b the respective time delays τa and τb are introduced. Thus at the summation knots Q1 and Q2 respective beams characteristics are realized, e.g. respective forwards and rearwards cardioid beam patterns.
The two beam-characteristic signals which are the result of time-domain beam-forming in unit 3 are output from processing unit 3. The beam-characteristic lower-frequency signal SPb is summed at Q4 with the higher-frequent component SHPb from the output signal of converter 1b. In analogy, the lower-frequency time-domain beam-formed signal SPa is summed at Q3 with the higher-frequency component SHPa. The summing result of Q3 and Q4 are both time-to-frequency converted at unit 7a, 7b. The high-frequency components yet not processed are subsequently processed in frequency-domain beam-processing Pa and Pb, wherein e.g. the same beam-forming process is performed as in unit 3 but now in frequency-domain. As shown in FIG. 1, because the low-frequency components have already been beam-forming processed in time-domain by unit 3, these low-frequency components are just time-to-frequency converted—L—and reconverted into time-domain as are the outputs of frequency-domain beam-forming Pa and Pb in units IIa, IIb.
Clearly before establishing reconversion of the frequency-domain beam-forming signals—II—further signal processing in frequency-domain will normally be applied so as to establish a desired signal transfer characteristic between acoustical input to the converter arrangement 1 and a mechanical output from an electrical-to-mechanical output converter 13, to which the resulting electrical output audio signals are operationally connected (dash line). Thus, by means of the embodiment of FIG. 1 there has been shown beam-forming processing of an input audio signal, whereby the input audio signal Sin1 is separated into two parts, namely a higher-frequency and a lower-frequency part. The lower-frequency part only is processed by beam-forming in time-domain. The result signal of such time-domain beam-forming process is summed to the second signal part which consists of higher-frequency components. The summing result is subjected to frequency-domain beam-forming after respective time-to-frequency-domain conversion as is perfectly clear to the skilled artisan.
As may be seen in the specific example of FIG. 1 adding the respective low-frequency components L downstream the summing Q3 and Q4 reconstructs the omnidirectional low-frequency characteristics.
By time-domain processing in unit 3 and respective adjustment of the allpass filters phase mismatch compensation is achieved for the lower-frequency part. Also level mismatch of the input converters is compensated in time-domain processing of the lower-frequency part.
Most generically, the approach of combining time-domain and frequency-domain signal processing in fact in parallel on specific parts of a signal allows to selectively apply the optimum domain processing. As of FIG. 1, for the specific beam-forming lower-frequency parts are advantageously time-domain processed and higher-frequency parts are advantageously frequency-domain processed. Such an approach may be of high advantage for signal processing more generically than just for beam-forming.
In FIG. 2 the approach as of FIG. 1 is more generalized.
The electrical audio input signal Sin is separated at a unit 17 into two parts Sin1 and Sin2. The second part Sin2 is processed in time-domain P at unit 19 and the result is summed to the first part Sin1 at Q34. Both the unprocessed first part Sin1 and the time-domain processed second part SP are then processed in frequency-domain in unit 21.
Still with an eye on FIG. 1 it must be emphasized that the acoustical-to-mechanical input converter arrangement 1, the output electrical-to-mechanical converter arrangement 13 as well as all the processing as shown may be incorporated within one single hearing device. Nevertheless, the converter arrangement 1 and 13 may also be incorporated in two distinct hearing devices, e.g. of a binaural system. One or both converter arrangements 1, 13 may be provided at a hearing device and processing may be performed remote. Thus, time-domain and frequency-domain processing may be performed in a centralized processing architecture or in a decentralized, possibly with wireless intercommunication of the processes or units. In other words utmost flexibility is possible with respect to the architecture of the embodiment as shown in FIG. 1.
As was discussed above, one of the important considerations to decide which part of an electric audio signal is to be processed in time-domain and which part is to be processed in frequency-domain is matching of the input acoustical-to-electrical converters as of 1a and 1b. If matching is the only topic to be resolved before further signal processing, which further processing may be realized in either of the two domains without specific preference, the signal processing as shown in FIG. 3 may be performed. Here parallel time-domain and frequency-domain processing is performed. According to FIG. 3 the two components Sa and Sb of Sin are again and as was explained in context with FIG. 1 separate in two parts, the lower-frequency part SLP and the higher-frequency part SHP. The former is processed to compensate for low-frequency mismatch of the converters 1a and 1b in time-domain matching unit 33.
There results output signal SLPM with low-frequency-matched SLPMa and SLPMb.
In analogy the higher-frequency part SHP comprising SHPa and SHPb is matched by frequency-domain matching process M in unit 35.
In FIG. 3 time-to-frequency conversion as well as frequency-to-time-domain conversion has been omitted for simpleness.
At the output of unit 35 two matched high-frequency signals are generated. The lower-frequency matched signal SLPM and the higher-frequency matched signal SHPM, after respective conversion and/or reconversion, are summed, resulting in output signals Souta and Soutb. The signals SOUT is further processed, be it in time or in frequency-domain to establish the desired transfer characteristic between input acoustical signal Sin and output mechanical signal of a hearing device.
In FIG. 4 there is shown, in analogy to FIG. 2, the more generalized processing as of FIG. 3. The electric audio input signal Sin is separated in a first part Sin1 and a second part Sin2. The first part is frequency-domain processed as shown by P, whereas the second part is processed in time-domain, P.
The processing results are summed in unit 39. Thus, and according to FIGS. 3 and 4 there is performed parallel time-domain and frequency-domain processing. In FIGS. 3 and 4 both processings are in fact equal but performed in frequency mode for higher frequencies and in time-domain mode for lower frequencies. It is perfectly clear that the principal of the present invention with respect to manufacturing an output electric audio signal, may also be achieved and followed up by applying completely different time-domain and frequency-domain processings if the two signal parts are to be differently treated.
Thus, and as has been shown, by the present invention the advantages of time-domain and frequency-domain processing are specifically exploited in combination.
Patent Application
20070269066
