CA2427845C - Method for verifying the availability of a signal component and device for carrying out said method - Google Patents
Method for verifying the availability of a signal component and device for carrying out said method Download PDFInfo
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- CA2427845C CA2427845C CA2427845A CA2427845A CA2427845C CA 2427845 C CA2427845 C CA 2427845C CA 2427845 A CA2427845 A CA 2427845A CA 2427845 A CA2427845 A CA 2427845A CA 2427845 C CA2427845 C CA 2427845C
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2225/00—Details of deaf aids covered by H04R25/00, not provided for in any of its subgroups
- H04R2225/43—Signal processing in hearing aids to enhance the speech intelligibility
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- Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
Abstract
The invention relates to a method and a device which are used to verify the availability of a signal component (s) in an input signal (x). The method consists in the following: a measure (fest) for the frequency of the input signal (x) is produced from said input signal (x); the variance of said measure (fest) for the frequency of the input signal (x) is determined; the variance (v) thus determined is compared to a given threshold value (LT); the availability of the signal component (s) is confirmed if the variance (v) lies within a given range with respect to the predetermined threshold value (LT).
The availability of a signal component(s) in an input signal (x) can be determined quickly and easily, requiring only a few operations.The inventive method and device for carrying out said method are particularly suitable for use with mobile devices, e.g. hearing devices.
The availability of a signal component(s) in an input signal (x) can be determined quickly and easily, requiring only a few operations.The inventive method and device for carrying out said method are particularly suitable for use with mobile devices, e.g. hearing devices.
Description
METHOD FOR VERIFYING THE AVAILABILITY OF A SIGNAL COMPONENT
AND DEVICE FOR CARRYING OUT SAID METHOD
The present invention is related to a method according to the pre-characterizing part of claim l, to a usa of the method as well as a device to perform the method.
The detection of a narrow band signal component, as e.g. a sinusoidal signal in a noise signal, is a problem to be solved very often. To solve this problem different known methods are available. A first method is using correlation calculations, a second is a method based on parametrizing followed by peak picking, and a third is using a number of zero crossing counters.
All these known methods bear the drawback that high computer power is necessary because of the complex algorithms which must be applied. In pa=ticular, this is the case if speech signals are being processed. Possible fields of application are telecommunication products, audio products or hearing devices, whereas in the following under the term "hearing device" so-called hearing aids, which are used to correct an impaired hearing of a person as well as all other acoustical communication systems, as for example radio sets, must be understood.
" CA 02427845 2003-05-02 The present invention therefore has the object to provide a method which does not incorporate the above-mentioned drawbacks.
This object is obtained by the el~mer_ts provided in the characterizing part of claim 1. Advantageous embodiments of the method according to the present invention, a use of the method as well as a device to perform the method are given in further claims.
The method according to the present invention is characterized by a number of very simple method steps, which can be performed by using little computer power.
Therefore, the method according to the present invention qualifies in particular for the use in systems having restricted access to energy supply, as for example for mobile devices which must be power line independent, or for systems in which the occurrence of a signal component must be determined very quickly.
In further embodiments of the present invention it is proposed to use the method for the detection and elimination of signal feedback. Signal feedback is a known problem in hearing devices, in mobile telephones and other telecommunication products. A number of solutions have beer.
elaborated by the telecommunication industry. It is known to attenuate the signals in the signal feedback path by corresponding adjustment of the attenuation in the transfer P202978 - 1074020.doc ' CA 02427845 2003-05-02 function in the feedback path. Furthermore, the use of auto- ar_d/or cross correlations schemes has been envisioned by which the correlation of the input signal and the outpu signal are calcula=ed in the time domain or in the frequency domain. The results of the calculations are used to adjust the transfer function in the signal feedback path, using the LMS-(Least Nlear_ Square)-algorithm (feedback canceller). Alternatively, the results of the calculations are used to adjust the transfer function in the forward path, whereby the loop gain is reduced at the critical frequencies.
For further information on the known methods it is referred to the following printings: US-5 680 467, EP-0 656 737, WO
99/26453, WO 99/51059, DE-197 48 079.
The known methods have been used successfully but have the drawback that again a high computer power is necessary to obtain useful results. The use of the known algorithms in hearing devices leads to an increased energy usage. As a result thereof, the operating time until the next recharge or replacement of the batteries is reduced, which reduction is basically undesired.
In case the loop gain reaches a value which is greater than one in a given frequency range, and in case the magnitude of signal components is some decibels lower at other frequencies than the frequency of the feedback signal if P202978 - 1079020.doc the gain is increased in the forward path, then a notch filter according to the present invention can be used to reduce the signal feedback. In case that different critical frequencies lie too far apart, several notcr. filters can be used according to a further embodiment of the present invention.
In order that a notch filter can be adjusted to the critical frequency, i.e. the feedback frequency, the critical frequency must be detected first. According to the invention this is performed by the calculation of the variance of the measure for the frequency of the input signal, whereas signal feedback is being detected if the variance lies within a predetermined range in relation to a predetermined limit value.
The invention will be further explained in the following by referring to drawings which show exemplified embodiments, wherein:
Fig. 1 shows a magnitude spectrum of an input signal having a superimposed narrow bandwidth signal component;
Fig. 2 shows a block diagram of a circuit arrangement for checking of an occurrence of a signal component in the input signal;
P202979 - 1074020.dcc ' CA 02427845 2003-05-02 Fig. 3 shows a block diagram of a circc,it arrangement for the detection and elimination of a signal feedback component, and Fig. 4 shows a further specific embodiment of the circuit arrangement according to fig. 3.
fig. 1 shows a magnitude spectrum, i.e. the magnitude of an input signal x in function of the frequency f. In a frequency range B, which is limited by the upper and lower frequency fB~l and f~~~, respectively, a narrow bandwith signal component s with a middle frequency fkrit is identifiable. The magnitude at the frequency Brit lies some dB (Decibel) higher than the rest of the input signals x in the frequency range B. In a first embodiment of the present inventicn it is provided to detect the occurrence of the signal component s. A circuit arrangement, which can be used therefore, is schematically shown in Fig. 2. In a second embodiment of the present invention, it is provided to eliminate a detected signal component s from the input signal x, which signal component s emerged e.g. from a signal feedback. If the elimination of the signal component s cannot be reached, it is at least possible to attenuate the signal component s in a desired measure. Possible circuit arrangements, which can be used to perform this task, are schematically shown in figs. 3 and 4.
P202978 - 1074020.doc According to fig. 2, a number of functional units are connected in series, starting with a band pass filter 1, an estimator unit 2, a variance unit 3 and a comparator unit 4. The input signal x, which consists either of an exploitable signal a or of an exploitable signal a and a superimposed signal component s, is fed tc the band pass filter 1 having upper and lower limit frequencies f9~1 and fap2 according to fig. 1, whereas it is assumed that the signal component s, if it exists, lies within the frequency range B (fig. 1). The band-limited signal, i.e. the output signal of the band pass filter 1, is fed to the estimator unit 2, in which a measure feet for the frequency of the input signal s is determined.
The term measure felt for the frequency of the input signal x basically means any frequency-dependent function.
It is proposed that as a first function y1 of the expected value of the magnitude of a low-pass filter is used. In time-discrete format, such a function can be stated as follows:
y,~n~=Ej~.r~n~+x~n-1~~
and in the z-plain, respectively, P202978 - 1074020.doc Y, (r)=E~l+=-'I ~IX(_~}, whereas a normalization is preferably performed using the level of the input signal x in order that the level itself does not have an influence o~ the measure fe3~ for tre frequency. For the last mentioned reason, two functions are necessary, of which at least one is frequency-dependent.
As second function y2, a corresponding high-pass filter, or much easier, merely the expected value of the magnitude of the input signals x, is chosen:
YZ = E~~~n By dividing the function y1 by the function y~ the desired measure felt for the frequency of the input signal x, which is now magnitude-independent, is obtained, namely:
f,~r(n)-E~x~n~+x(n-l~j- 2.~1+cosco E x(n), whereby co refers to the angular frequency.
P202978 - 1074020.doc - c3 -The determination of the erected value can also be approximated by an moving averages of first order, which can be described by the following equation:
whereas r and whereas T corresponds to the sample interval and i corresponds to a time constant having a value of approx. 20 ms.
Whether a signal component s in the input signal x exists, can be determined by calculating the variances v of the measure felt for the frequency. Therefore, the variances unit 3 according to fig. 2 is provided. If the variance v lies below a given limit value LT, it can be concluded that a narrow band-width, frequency-stable signal component s exists in the frequency range B (fig. 1). As a prerequisite it is mandatory that signal component s, if it exists, bears a certain stability and that the exploitable signal a is stable in this sense. Information regarding the calculation of the variance can be obtained, for example, from the standard work of Athanasios Papoulis entitled "Probability, Random Variables, and Stochastic Processes"
(P~lcGraca-Hill, 19$4, page 108 ff. ) .
p2o297a - 10~~o2o.ao~
' CA 02427845 2003-05-02 - g _ The mentioned comparison of tze calculated variance v and the predetermined limit value LT takes place in the comparator unit 4 raving an output signal of either zero or one, depending on whether the variance v is larger than the limit value LT or vice versa.
The method according to the present invention described along with fig. 2 can be used in particular for the detection of a punch of a pushbutton of a telecommunication terminal supporting frequency dialing. As is generally known, each of the twelve pushbuttons of such a terminal is coded by two of a total of seven sinusoidal signals, whereas the frequencies of the signals are known. The detection of punching one cf the pushbuttons is therefore limited to check the occurrence of signals having corresponding frequencies. According to the two detected frequencies the pushbuttons being punched can be identified, whereas the circuit arrangement according to fig. 2 can be used for each possible signal. Thereby, the band-pass filter is adjusted in such a way that only one signal can pass through the band-pass filter. Naturally, there exists the possibility that a filter bank consisting of seven band-pass filters to select each of the single possible signals is provided and that the further processing of the signals in the estimator unit 2, in the variance unit 3 and in the comparator unit 4 is dealt with in. a time multiplex process.
e~oL~~a - 1074020.doc Fig. 3 shows a further block diagram of a Further embodiment whicr: is based or. tha one shcwn in fig. 2. The block diagra~r shown above the dashed line ir. fig. 3 is exactly the same as the one shown in fig. 2. Below the dashed line according to fig. 3 a filter unit 6, a coefficient ca?cuiation unit 5 and a switching unit 7 are provided.
The input signal x fed to the band-pass filter 1 is further connected to the filter unit 6 and to one of the two switching contacts S2 of the switching unit 7. The output signal of the filter unit 6 is connected to the further switching contact S1. Furthermore, the measure felt for the frequency of the input signals x is fed to the coefficient calculation unit 5, in which the coefficients of the filter implemented in the filter unit 6 are calculated in a way yet to describe. The calculated coefficients will be transferred to the filter unit 6 as soon as the coefficients are determined. The determination of the measure felt for the frequency can be provided in a way described along with fig. 2.
Finally, either the input signal x directly or the output signal of the filter unit 6 will be switched to the output z in the switching unit 7 according to a control signal generated in a comparator unit 4. Ir_ other words, the input signal x is either filtered in the filter unit 6 or the input signal x will be passed to the output z without being processed. The switching is advantageously done in a P2029?3 - 1074020.doc "so=tly", which means tha transition from one stage to ancther is done is a smooth way.
As a consequence, the method according to the invention and the device according to the invention, respectively, can be advantageously used to detect and eliminate a feedback signal, to be precise, for telecommunication products as well as for hearing devices, whereas the computer power necessary for the calculations is diminishing. As a result, in particular when using the method according to the invention in a hearing device, the energy consumption can be held at a low level for the additional computational efforts.
In case that the signal component s must be suppressed by the filter unit 6, or at least attenuated, the filter unit 6 is realized as notch filter, whereas the maximum attenuation of the notch filter must lie in the middle of the frequency fkrit to be suppressed (fig. 1) . A notch filter can be realized according to the following equation:
H~z~=1+b' ~z-' +bz ~z-Z
whereas b' =-2~r~cosr~
and b,=rz.
P202978 - 1074020.doc " CA 02427845 2003-05-02 The notcr, filter according to the above meraioned equation features one single zero having a distance of radius r to the origin. It is proposed tc fix the radius r, for eaa~nple by giving it the value 0.98, whereas only cos a~ has to be determined in order to determine the coefficient b,. This value can be derived according to tre present invention from the measure feet for the frequency of the input signal x by solving the above mentioned equation for the measure felt for cos w. One can obtain the following equation:
b' _ _2 . r , .f2st _ 1 In a further embodiment of the present invention, it is provided to determine the notch filter according to the following equation:
H~w~ _ 1+b' ~~-' +b, .r-z _~ .
1+a' ~z-' +a: ~z whereas a' _-2~rP ~cosco , b'=-2~rZ~cosr.~, and a~=rP, P20297$ - 1074020.doc bi - rz .
The equations mentioned above can again be solved far cos cu in an analogous way. Hereby, the following two equations can be obtained:
av =-2.rP. .f2r _1 and b, _ -2 . rz _ .f2s' _ 1 The equations mentioned above describe thereby an algorithm for the estimation of a narrow bandwidth signal component s and, at the same time, allow obtaining coefficients for the notch filter to suppress the signal component s.
Fig. 4 shows a specific embodiment of the schematic representation of the present invention according to the block diagram of fig. 3. The processing units designated in fig. 3 are identified by dashed lines in fig. 4, whereby the same reference signs are used as in fig. 3.
In the estimator unit 2, the block diagram according to the equations, which have been described in connection with fig. 2, is shown. Besides the units resulting directly from the above mentioned equations and which units are not P202978 - 1074020.doc further explained, two decimation. units 10 and 11 are providzd in addition, which are provided before a quotient unit 12 and which reduce the data rate in order to reduce the already reduced computational effort even further.
Methods for the data rate reduction are generally known and are further explained, ~cr~example, ir_ the standard work of R.E. Crochiere et al. entitled "Multirate Digi~al Signal Processing" (Prentice-Hail Signal Processing Series, Prentice-1-iall, Inc. , Engl ewood Cl iffs, DTew tersey, 1983) .
Sufficient anti aliasi.ng filters are implicitly provided before the actual decimation.
Without the decimation units 10 and 11 the measure felt for the frequency of the input signal x can be obtained at the output of the estimator unit 2, as has been explained along with fig. 2:
.fesan~= E~~~n~+r~n-l~i E x(n)) Considering tha above mentioned explanations, in particular the one made in connection with the block diagram shown in figs. 2 and 3, a probability measure fbprQb for the feedback can be determined from the input signal x according to the following equation in the variances unit 3 or in the comparator unit 4, respectively:
P202978 - 1074020.doc J "prob = max 1- k ~ E E{fefr I - fest ~O
J
whereas k represents a sensitivity parameter through which the amount of ir_fluence of the control mechanism is determined. According to fig. 4 the probability measure fbp=ob is not yet the output signal of the comparator unit 4 since it is necessary to change the data rate in interpolator unit 13, in which a data rate reduction is performed analogously to the data rate increase in the decimation units 10 and 11, i.e. in the interpolation unit 13 the data stream is readjusted to the original data rate of the input signal x.
In the above mentioned equation for the probability measure fbProb the expected value E{...} is again realized, in the simplest embodiment of the method according to the present invention, as a moving averager with a short time constant for a signal follow-up towards larger signal values, but with a long time constant for the signal follow-up towards smaller signal values. Such a moving averager is also called a fast attack - slow release averager. A
corresponding moving averager 14 is connected to the output of the comparator unit 4. Thereby, the control behavior of the closed loop control circuit is further improved.
P202978 - ~074020.doc ' CA 02427845 2003-05-02 The expected value designated E~..} is a symmetric moving averages which means that the attaci and release time constants are equal.
In tre filter unit 6 a notch filter according to the follocaing equation is realized:
HtZ) 1 ~' fbprob ~ \b1 ~ ~ ~ '~w b' . ~pnob ~ Z ' whereas the coefficients b1 and b2 are determined as follows in the coefficient calculation unit 5:
b~ _ -2 ~ r ~ 'fe$' -1 and bz=rz.
The radius r is again the distance from the zero to the origin in the z-plane and is preferably fix. It could have been shown that it is advantageous to choose a value of 0.98 for the radius r. Instead of the above mentioned specific transfer function for the notch filter the general form is shown in the following, which is preferably used:
P202978 - 1074020.doc H ~- ~ _ _1 + ~prob ' \b! ' .. -~- b, ' l uprob fi ~_1 ~, __, r 1 -~- J bprob ' al ' " -~- a2 ' J "prob ' whereas z bt - -7 , rl , -Pest - 1 7 r al = -7 . rp . fesr - 1 b2=rz, a, = rP and ~prob =lnax 1-k'E E~f'~t~-,fesr ~~
With r, a constant is referenced having a value of preferably 0.98; k is a sensitivity parameter for the adjustment of control characteristics, whereas the value for k is preferably equal to 10.
P202978 - 1074020.doc
AND DEVICE FOR CARRYING OUT SAID METHOD
The present invention is related to a method according to the pre-characterizing part of claim l, to a usa of the method as well as a device to perform the method.
The detection of a narrow band signal component, as e.g. a sinusoidal signal in a noise signal, is a problem to be solved very often. To solve this problem different known methods are available. A first method is using correlation calculations, a second is a method based on parametrizing followed by peak picking, and a third is using a number of zero crossing counters.
All these known methods bear the drawback that high computer power is necessary because of the complex algorithms which must be applied. In pa=ticular, this is the case if speech signals are being processed. Possible fields of application are telecommunication products, audio products or hearing devices, whereas in the following under the term "hearing device" so-called hearing aids, which are used to correct an impaired hearing of a person as well as all other acoustical communication systems, as for example radio sets, must be understood.
" CA 02427845 2003-05-02 The present invention therefore has the object to provide a method which does not incorporate the above-mentioned drawbacks.
This object is obtained by the el~mer_ts provided in the characterizing part of claim 1. Advantageous embodiments of the method according to the present invention, a use of the method as well as a device to perform the method are given in further claims.
The method according to the present invention is characterized by a number of very simple method steps, which can be performed by using little computer power.
Therefore, the method according to the present invention qualifies in particular for the use in systems having restricted access to energy supply, as for example for mobile devices which must be power line independent, or for systems in which the occurrence of a signal component must be determined very quickly.
In further embodiments of the present invention it is proposed to use the method for the detection and elimination of signal feedback. Signal feedback is a known problem in hearing devices, in mobile telephones and other telecommunication products. A number of solutions have beer.
elaborated by the telecommunication industry. It is known to attenuate the signals in the signal feedback path by corresponding adjustment of the attenuation in the transfer P202978 - 1074020.doc ' CA 02427845 2003-05-02 function in the feedback path. Furthermore, the use of auto- ar_d/or cross correlations schemes has been envisioned by which the correlation of the input signal and the outpu signal are calcula=ed in the time domain or in the frequency domain. The results of the calculations are used to adjust the transfer function in the signal feedback path, using the LMS-(Least Nlear_ Square)-algorithm (feedback canceller). Alternatively, the results of the calculations are used to adjust the transfer function in the forward path, whereby the loop gain is reduced at the critical frequencies.
For further information on the known methods it is referred to the following printings: US-5 680 467, EP-0 656 737, WO
99/26453, WO 99/51059, DE-197 48 079.
The known methods have been used successfully but have the drawback that again a high computer power is necessary to obtain useful results. The use of the known algorithms in hearing devices leads to an increased energy usage. As a result thereof, the operating time until the next recharge or replacement of the batteries is reduced, which reduction is basically undesired.
In case the loop gain reaches a value which is greater than one in a given frequency range, and in case the magnitude of signal components is some decibels lower at other frequencies than the frequency of the feedback signal if P202978 - 1079020.doc the gain is increased in the forward path, then a notch filter according to the present invention can be used to reduce the signal feedback. In case that different critical frequencies lie too far apart, several notcr. filters can be used according to a further embodiment of the present invention.
In order that a notch filter can be adjusted to the critical frequency, i.e. the feedback frequency, the critical frequency must be detected first. According to the invention this is performed by the calculation of the variance of the measure for the frequency of the input signal, whereas signal feedback is being detected if the variance lies within a predetermined range in relation to a predetermined limit value.
The invention will be further explained in the following by referring to drawings which show exemplified embodiments, wherein:
Fig. 1 shows a magnitude spectrum of an input signal having a superimposed narrow bandwidth signal component;
Fig. 2 shows a block diagram of a circuit arrangement for checking of an occurrence of a signal component in the input signal;
P202979 - 1074020.dcc ' CA 02427845 2003-05-02 Fig. 3 shows a block diagram of a circc,it arrangement for the detection and elimination of a signal feedback component, and Fig. 4 shows a further specific embodiment of the circuit arrangement according to fig. 3.
fig. 1 shows a magnitude spectrum, i.e. the magnitude of an input signal x in function of the frequency f. In a frequency range B, which is limited by the upper and lower frequency fB~l and f~~~, respectively, a narrow bandwith signal component s with a middle frequency fkrit is identifiable. The magnitude at the frequency Brit lies some dB (Decibel) higher than the rest of the input signals x in the frequency range B. In a first embodiment of the present inventicn it is provided to detect the occurrence of the signal component s. A circuit arrangement, which can be used therefore, is schematically shown in Fig. 2. In a second embodiment of the present invention, it is provided to eliminate a detected signal component s from the input signal x, which signal component s emerged e.g. from a signal feedback. If the elimination of the signal component s cannot be reached, it is at least possible to attenuate the signal component s in a desired measure. Possible circuit arrangements, which can be used to perform this task, are schematically shown in figs. 3 and 4.
P202978 - 1074020.doc According to fig. 2, a number of functional units are connected in series, starting with a band pass filter 1, an estimator unit 2, a variance unit 3 and a comparator unit 4. The input signal x, which consists either of an exploitable signal a or of an exploitable signal a and a superimposed signal component s, is fed tc the band pass filter 1 having upper and lower limit frequencies f9~1 and fap2 according to fig. 1, whereas it is assumed that the signal component s, if it exists, lies within the frequency range B (fig. 1). The band-limited signal, i.e. the output signal of the band pass filter 1, is fed to the estimator unit 2, in which a measure feet for the frequency of the input signal s is determined.
The term measure felt for the frequency of the input signal x basically means any frequency-dependent function.
It is proposed that as a first function y1 of the expected value of the magnitude of a low-pass filter is used. In time-discrete format, such a function can be stated as follows:
y,~n~=Ej~.r~n~+x~n-1~~
and in the z-plain, respectively, P202978 - 1074020.doc Y, (r)=E~l+=-'I ~IX(_~}, whereas a normalization is preferably performed using the level of the input signal x in order that the level itself does not have an influence o~ the measure fe3~ for tre frequency. For the last mentioned reason, two functions are necessary, of which at least one is frequency-dependent.
As second function y2, a corresponding high-pass filter, or much easier, merely the expected value of the magnitude of the input signals x, is chosen:
YZ = E~~~n By dividing the function y1 by the function y~ the desired measure felt for the frequency of the input signal x, which is now magnitude-independent, is obtained, namely:
f,~r(n)-E~x~n~+x(n-l~j- 2.~1+cosco E x(n), whereby co refers to the angular frequency.
P202978 - 1074020.doc - c3 -The determination of the erected value can also be approximated by an moving averages of first order, which can be described by the following equation:
whereas r and whereas T corresponds to the sample interval and i corresponds to a time constant having a value of approx. 20 ms.
Whether a signal component s in the input signal x exists, can be determined by calculating the variances v of the measure felt for the frequency. Therefore, the variances unit 3 according to fig. 2 is provided. If the variance v lies below a given limit value LT, it can be concluded that a narrow band-width, frequency-stable signal component s exists in the frequency range B (fig. 1). As a prerequisite it is mandatory that signal component s, if it exists, bears a certain stability and that the exploitable signal a is stable in this sense. Information regarding the calculation of the variance can be obtained, for example, from the standard work of Athanasios Papoulis entitled "Probability, Random Variables, and Stochastic Processes"
(P~lcGraca-Hill, 19$4, page 108 ff. ) .
p2o297a - 10~~o2o.ao~
' CA 02427845 2003-05-02 - g _ The mentioned comparison of tze calculated variance v and the predetermined limit value LT takes place in the comparator unit 4 raving an output signal of either zero or one, depending on whether the variance v is larger than the limit value LT or vice versa.
The method according to the present invention described along with fig. 2 can be used in particular for the detection of a punch of a pushbutton of a telecommunication terminal supporting frequency dialing. As is generally known, each of the twelve pushbuttons of such a terminal is coded by two of a total of seven sinusoidal signals, whereas the frequencies of the signals are known. The detection of punching one cf the pushbuttons is therefore limited to check the occurrence of signals having corresponding frequencies. According to the two detected frequencies the pushbuttons being punched can be identified, whereas the circuit arrangement according to fig. 2 can be used for each possible signal. Thereby, the band-pass filter is adjusted in such a way that only one signal can pass through the band-pass filter. Naturally, there exists the possibility that a filter bank consisting of seven band-pass filters to select each of the single possible signals is provided and that the further processing of the signals in the estimator unit 2, in the variance unit 3 and in the comparator unit 4 is dealt with in. a time multiplex process.
e~oL~~a - 1074020.doc Fig. 3 shows a further block diagram of a Further embodiment whicr: is based or. tha one shcwn in fig. 2. The block diagra~r shown above the dashed line ir. fig. 3 is exactly the same as the one shown in fig. 2. Below the dashed line according to fig. 3 a filter unit 6, a coefficient ca?cuiation unit 5 and a switching unit 7 are provided.
The input signal x fed to the band-pass filter 1 is further connected to the filter unit 6 and to one of the two switching contacts S2 of the switching unit 7. The output signal of the filter unit 6 is connected to the further switching contact S1. Furthermore, the measure felt for the frequency of the input signals x is fed to the coefficient calculation unit 5, in which the coefficients of the filter implemented in the filter unit 6 are calculated in a way yet to describe. The calculated coefficients will be transferred to the filter unit 6 as soon as the coefficients are determined. The determination of the measure felt for the frequency can be provided in a way described along with fig. 2.
Finally, either the input signal x directly or the output signal of the filter unit 6 will be switched to the output z in the switching unit 7 according to a control signal generated in a comparator unit 4. Ir_ other words, the input signal x is either filtered in the filter unit 6 or the input signal x will be passed to the output z without being processed. The switching is advantageously done in a P2029?3 - 1074020.doc "so=tly", which means tha transition from one stage to ancther is done is a smooth way.
As a consequence, the method according to the invention and the device according to the invention, respectively, can be advantageously used to detect and eliminate a feedback signal, to be precise, for telecommunication products as well as for hearing devices, whereas the computer power necessary for the calculations is diminishing. As a result, in particular when using the method according to the invention in a hearing device, the energy consumption can be held at a low level for the additional computational efforts.
In case that the signal component s must be suppressed by the filter unit 6, or at least attenuated, the filter unit 6 is realized as notch filter, whereas the maximum attenuation of the notch filter must lie in the middle of the frequency fkrit to be suppressed (fig. 1) . A notch filter can be realized according to the following equation:
H~z~=1+b' ~z-' +bz ~z-Z
whereas b' =-2~r~cosr~
and b,=rz.
P202978 - 1074020.doc " CA 02427845 2003-05-02 The notcr, filter according to the above meraioned equation features one single zero having a distance of radius r to the origin. It is proposed tc fix the radius r, for eaa~nple by giving it the value 0.98, whereas only cos a~ has to be determined in order to determine the coefficient b,. This value can be derived according to tre present invention from the measure feet for the frequency of the input signal x by solving the above mentioned equation for the measure felt for cos w. One can obtain the following equation:
b' _ _2 . r , .f2st _ 1 In a further embodiment of the present invention, it is provided to determine the notch filter according to the following equation:
H~w~ _ 1+b' ~~-' +b, .r-z _~ .
1+a' ~z-' +a: ~z whereas a' _-2~rP ~cosco , b'=-2~rZ~cosr.~, and a~=rP, P20297$ - 1074020.doc bi - rz .
The equations mentioned above can again be solved far cos cu in an analogous way. Hereby, the following two equations can be obtained:
av =-2.rP. .f2r _1 and b, _ -2 . rz _ .f2s' _ 1 The equations mentioned above describe thereby an algorithm for the estimation of a narrow bandwidth signal component s and, at the same time, allow obtaining coefficients for the notch filter to suppress the signal component s.
Fig. 4 shows a specific embodiment of the schematic representation of the present invention according to the block diagram of fig. 3. The processing units designated in fig. 3 are identified by dashed lines in fig. 4, whereby the same reference signs are used as in fig. 3.
In the estimator unit 2, the block diagram according to the equations, which have been described in connection with fig. 2, is shown. Besides the units resulting directly from the above mentioned equations and which units are not P202978 - 1074020.doc further explained, two decimation. units 10 and 11 are providzd in addition, which are provided before a quotient unit 12 and which reduce the data rate in order to reduce the already reduced computational effort even further.
Methods for the data rate reduction are generally known and are further explained, ~cr~example, ir_ the standard work of R.E. Crochiere et al. entitled "Multirate Digi~al Signal Processing" (Prentice-Hail Signal Processing Series, Prentice-1-iall, Inc. , Engl ewood Cl iffs, DTew tersey, 1983) .
Sufficient anti aliasi.ng filters are implicitly provided before the actual decimation.
Without the decimation units 10 and 11 the measure felt for the frequency of the input signal x can be obtained at the output of the estimator unit 2, as has been explained along with fig. 2:
.fesan~= E~~~n~+r~n-l~i E x(n)) Considering tha above mentioned explanations, in particular the one made in connection with the block diagram shown in figs. 2 and 3, a probability measure fbprQb for the feedback can be determined from the input signal x according to the following equation in the variances unit 3 or in the comparator unit 4, respectively:
P202978 - 1074020.doc J "prob = max 1- k ~ E E{fefr I - fest ~O
J
whereas k represents a sensitivity parameter through which the amount of ir_fluence of the control mechanism is determined. According to fig. 4 the probability measure fbp=ob is not yet the output signal of the comparator unit 4 since it is necessary to change the data rate in interpolator unit 13, in which a data rate reduction is performed analogously to the data rate increase in the decimation units 10 and 11, i.e. in the interpolation unit 13 the data stream is readjusted to the original data rate of the input signal x.
In the above mentioned equation for the probability measure fbProb the expected value E{...} is again realized, in the simplest embodiment of the method according to the present invention, as a moving averager with a short time constant for a signal follow-up towards larger signal values, but with a long time constant for the signal follow-up towards smaller signal values. Such a moving averager is also called a fast attack - slow release averager. A
corresponding moving averager 14 is connected to the output of the comparator unit 4. Thereby, the control behavior of the closed loop control circuit is further improved.
P202978 - ~074020.doc ' CA 02427845 2003-05-02 The expected value designated E~..} is a symmetric moving averages which means that the attaci and release time constants are equal.
In tre filter unit 6 a notch filter according to the follocaing equation is realized:
HtZ) 1 ~' fbprob ~ \b1 ~ ~ ~ '~w b' . ~pnob ~ Z ' whereas the coefficients b1 and b2 are determined as follows in the coefficient calculation unit 5:
b~ _ -2 ~ r ~ 'fe$' -1 and bz=rz.
The radius r is again the distance from the zero to the origin in the z-plane and is preferably fix. It could have been shown that it is advantageous to choose a value of 0.98 for the radius r. Instead of the above mentioned specific transfer function for the notch filter the general form is shown in the following, which is preferably used:
P202978 - 1074020.doc H ~- ~ _ _1 + ~prob ' \b! ' .. -~- b, ' l uprob fi ~_1 ~, __, r 1 -~- J bprob ' al ' " -~- a2 ' J "prob ' whereas z bt - -7 , rl , -Pest - 1 7 r al = -7 . rp . fesr - 1 b2=rz, a, = rP and ~prob =lnax 1-k'E E~f'~t~-,fesr ~~
With r, a constant is referenced having a value of preferably 0.98; k is a sensitivity parameter for the adjustment of control characteristics, whereas the value for k is preferably equal to 10.
P202978 - 1074020.doc
Claims (18)
1. Method for verifying an occurrence of a signal component (s) in an input signal (x), whereas the method consists in - that a measure (f est) for the frequency of the input signal (x) is generated from the input signal (x), - that a variance (v) of the measure (f est) for the frequency is determined of the input signal (x), - that the determined variance (v) is compared to a preset limit value (LT), and - that the occurrence of the signal components (s) is confirmed if the variance (v) lies within a predetermined range in relation to the preset limit value (LT).
2. Method according to claim 1, characterized in that the occurrence of the signal components (s) is confirmed if the variance (v) is smaller than the preset limit value (LT).
3. Method according to claim 1 or 2, characterized in that the signal component (s) is suppressed in the input signal (x).
4. Method according to one of the claims 1 to 3, characterized in that the input signal (x) is band-limited before the measure (f est) nor the frequency is generated.
5. Method according to one of the claims 1 to 4, characterized in that the measure (f est) for the frequency is determined by dividing of at least two functions, of which at least one is frequency-dependent.
6. Method according to claim 5, characterized in that the measure (f est) for the frequency is determined from dividing of two functions, one of which having a low-pass filter transfer function and the other function corresponds to the expected value of the input signal.
7. Method according to one of the claims 3 to 6, characterized in that a notch filter (6) is used to suppress the signal components (s) in the input signal (x), whereas as transfer function for the notch filter (6) the following equation is used:
whereas a1 = -2.cndot.r p.cndot.cos.omega., b1 = -2.cndot.r z.cndot.cos.omega., and a2 = r~
b2 = r~.
whereas a1 = -2.cndot.r p.cndot.cos.omega., b1 = -2.cndot.r z.cndot.cos.omega., and a2 = r~
b2 = r~.
8. Method according to one of the claims 3 to 6, characterized in that a notch filter (6) is used to suppress the signal components (s) in the input signal (x), whereas as transfer function for the notch filter (6) the following equation is used:
whereas wherein r a constant having the value of 0.98 and k the sensitivity parameter to adjust the control characteristics, wherein the value for k is preferably equal to 10.
whereas wherein r a constant having the value of 0.98 and k the sensitivity parameter to adjust the control characteristics, wherein the value for k is preferably equal to 10.
9. Use of the method according to one of the claims 3 to 8 to suppress signal feedback.
10. Use of the method according to one of the claims 3 to 8 to suppress a signal feedback in a hearing device.
11. Use of the method according to claim 1 or 2 for the detection of a punch of a pushbutton of a telecommunication terminal having frequency dialing.
12. Device to perform the method according to claim 1 or 2, characterized in that an input signal (x) is operationally connected to an estimator unit (2) to determine a measure (f est) for the frequency of the input signal (x) and that the measure (f est) for the frequency is fed to a variances unit (3), the output signal of the variances unit (3) is operationally coupled to a comparator unit (4), which is further being fed by a preset limit value (LT).
13. Device to perform the method according to one of the claims 3 to 8, characterized in that an input signal (x) is fed to an estimator unit (2) to determine a measure (f est) for the frequency of an input signal (x) and that the measure (f est) for the frequency of the input signal (x) is fed to a variances unit (3), the output signal (v) of the variances unit (3) is operationally coupled to the comparator unit (4), whereas the comparator unit (4) is further fed by a preset limit value (LT), that the measure (f est) for the frequency of the input signal (x) is further fed to a coefficient calculation unit (5) for the calculation of filter coefficients which are transferred to a filter unit (6), which is, on its input side, connected with the input signal (x) and which is, on its output side, connected with a first switch contact (S1) of a switching unit (7), whereas the input signal (x) is fed to a second switch contact (S2) of the switching unit (7) and that an output signal of the comparator unit (4) generates a control signal for the switching unit (7), whereby either the input signal (x) or the output signal of the filter unit (6) is switchable on the output (z) of the switching unit (7).
14. Device according to claim 13, characterized in that the filter unit (7) is a notch filter.
15. Device according to claim 14, characterized in that the notch filter contains zeros and possibly poles, which positions may be fixed by the measure (f est) of the frequency of the input signal (x).
16. Device according to one of the claims 12 to 15, characterized in that the measure (f est) for the frequency is obtained by dividing at least two functions of which at least one is frequency-dependent.
17. Device according to claim 16, characterized in that the measure (f est) for the frequency is obtained by dividing two functions, whereas one of the functions has a low-pass filter transfer function and the other of the two functions corresponds to the expected value of the input signal.
18. Hearing device according to one of the claims 13 to 17.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/CH2001/000607 WO2001095578A2 (en) | 2001-10-05 | 2001-10-05 | Method for verifying the availability of a signal component and device for carrying out said method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2427845A1 CA2427845A1 (en) | 2001-12-13 |
| CA2427845C true CA2427845C (en) | 2010-07-13 |
Family
ID=4358250
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2427845A Expired - Fee Related CA2427845C (en) | 2001-10-05 | 2001-10-05 | Method for verifying the availability of a signal component and device for carrying out said method |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1433295B1 (en) |
| AU (1) | AU2001291588A1 (en) |
| CA (1) | CA2427845C (en) |
| WO (1) | WO2001095578A2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102004050304B3 (en) * | 2004-10-14 | 2006-06-14 | Siemens Audiologische Technik Gmbh | Method for reducing feedback in an acoustic system and signal processing device |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5442696A (en) * | 1991-12-31 | 1995-08-15 | At&T Corp. | Method and apparatus for detecting control signals |
| US5353346A (en) * | 1992-12-22 | 1994-10-04 | Mpr Teltech, Limited | Multi-frequency signal detector and classifier |
| US5333191A (en) * | 1993-04-22 | 1994-07-26 | Interdigital Technology Corporation | Detection of multifrequency tone signals |
| EP0585976A3 (en) * | 1993-11-10 | 1994-06-01 | Phonak Ag | Hearing aid with cancellation of acoustic feedback |
| US6434246B1 (en) * | 1995-10-10 | 2002-08-13 | Gn Resound As | Apparatus and methods for combining audio compression and feedback cancellation in a hearing aid |
-
2001
- 2001-10-05 AU AU2001291588A patent/AU2001291588A1/en not_active Abandoned
- 2001-10-05 EP EP01971593A patent/EP1433295B1/en not_active Expired - Lifetime
- 2001-10-05 WO PCT/CH2001/000607 patent/WO2001095578A2/en active Application Filing
- 2001-10-05 CA CA2427845A patent/CA2427845C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| WO2001095578A2 (en) | 2001-12-13 |
| EP1433295A2 (en) | 2004-06-30 |
| EP1433295B1 (en) | 2011-09-28 |
| AU2001291588A1 (en) | 2001-12-17 |
| CA2427845A1 (en) | 2001-12-13 |
| WO2001095578A3 (en) | 2002-12-19 |
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