DE10202635A1 - Noise reduction method, e.g. for car radio receiver, involves varying audio signal passband with adaptive low-pass filter controlled according to received signal strength - Google Patents

Noise reduction method, e.g. for car radio receiver, involves varying audio signal passband with adaptive low-pass filter controlled according to received signal strength

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Publication number
DE10202635A1
DE10202635A1 DE2002102635 DE10202635A DE10202635A1 DE 10202635 A1 DE10202635 A1 DE 10202635A1 DE 2002102635 DE2002102635 DE 2002102635 DE 10202635 A DE10202635 A DE 10202635A DE 10202635 A1 DE10202635 A1 DE 10202635A1
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Germany
Prior art keywords
signal
digital
adaptive low
digital signal
input
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Granted
Application number
DE2002102635
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German (de)
Other versions
DE10202635B4 (en
Inventor
Christoph Benz
Stefan Gierl
Hans-Juergen Nitzpon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Harman Becker Automotive Systems GmbH
Original Assignee
Harman Becker Automotive Systems GmbH
Harman Becker Automotive Systems Becker Division GmbH
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Application filed by Harman Becker Automotive Systems GmbH, Harman Becker Automotive Systems Becker Division GmbH filed Critical Harman Becker Automotive Systems GmbH
Priority to DE2002102635 priority Critical patent/DE10202635B4/en
Publication of DE10202635A1 publication Critical patent/DE10202635A1/en
Application granted granted Critical
Publication of DE10202635B4 publication Critical patent/DE10202635B4/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H04B1/0028—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at baseband stage
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H04B1/0028—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at baseband stage
    • H04B1/0032—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at baseband stage with analogue quadrature frequency conversion to and from the baseband
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
    • H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
    • H04B1/14—Automatic detuning arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H04B1/1646—Circuits adapted for the reception of stereophonic signals
    • H04B1/1661—Reduction of noise by manipulation of the baseband composite stereophonic signal or the decoded left and right channels

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Analogue/Digital Conversion (AREA)

Abstract

A method for noise suppression in a digital signal path, where received signal strength is measured (P) and from this a control signal is derived and used to vary the cut-off frequency of an adaptive low pass filter (TP). When applied to a radio receiver, input audio signals (A) are digitized (AD), fed via a DSP stage (DP) and then filtered according to signal strength before being converted (DA) back into analog form (C). An Independent claim is included for a noise reduction circuit.

Description

Die Erfindung betrifft ein Verfahren und eine Schaltungsanordnung zur Rauschunterdrückung in einem digitalen Signalpfad. The invention relates to a method and a Circuit arrangement for noise suppression in a digital signal path.

Digitale Signale, wie z. B. digitale Audiosignale, die auf einem Signalpfad übertragen werden, sind mit Rauschen behaftet, was die Klangwiedergabe hörbar beeinträchtigt. Insbesondere bei kleinen Signalpegeln, die in der Nähe des Rauschpegels liegen, nimmt die Qualität der Klangwiedergabe deutlich ab. Digital signals such as B. digital audio signals based on are transmitted with a signal path, are subject to noise, which audibly affects the sound reproduction. In particular at low signal levels that are close to the noise level the quality of the sound reproduction decreases significantly.

Es sind daher Maßnahmen zur Rauschunterdrückung erforderlich, die jedoch möglichst preisgünstig sein sollten. Measures for noise suppression are therefore necessary which, however, should be as inexpensive as possible.

Es ist daher Aufgabe der Erfindung, ein Verfahren und eine Schaltungsanordnung zur Rauschunterdrückung so zu gestalten, daß mit nur geringem Aufwand eine erhebliche Reduktion des Rauschens erzielt wird. It is therefore an object of the invention, a method and a To design circuitry for noise suppression so that with little effort a significant reduction in Noise is achieved.

Verfahrensmäßig wird diese Aufgabe mit den im Anspruch 1 angegebenen Merkmalen dadurch gelöst, daß aus dem Signalpegel ein Steuersignal zur Steuerung eines im Signalpfad liegenden adaptiven Tiefpasses abgeleitet wird. In procedural terms, this task is carried out with specified features solved in that from the signal level Control signal for controlling a lying in the signal path adaptive low pass is derived.

Vorrichtungsmäßig wird diese Aufgabe mit den im Anspruch 4 angegebenen Merkmalen dadurch gelöst, daß im digitalen Signalpfad ein Signalprozessor und ein adaptiver Tiefpaß in Reihe liegen, daß am Eingang des digitalen Signalprozessors ein digitales Signal liegt, daß der Ausgang des digitalen Signalprozessors mit dem Eingang des adaptiven Tiefpasses und eines Pegelmessers verbunden ist, dessen Ausgang mit dem Eingang einer Auswerteeinheit verbunden ist und daß der Ausgang der Auswerteeinheit mit dem Steuereingang des adaptiven Tiefpasses verbunden ist. In terms of the device, this task is performed with specified features solved in that in digital Signal path a signal processor and an adaptive low pass in series lie that at the input of the digital signal processor digital signal lies that the output of the digital Signal processor with the input of the adaptive low pass and one Level meter is connected, the output of which is connected to the input of a Evaluation unit is connected and that the output of the Evaluation unit with the control input of the adaptive low pass connected is.

Die Erfindung sieht einen adaptiven Tiefpaß im Signalweg vor, dessen Parameter in Abhängigkeit vom Pegel des auf dem digitalen Signalpfad übertragenen digitalen Signals eingestellt werden. Der adaptive Tiefpaß bewirkt eine Bandbegrenzung des digitalen Signals und des Rauschens, so daß die Rauschleistung vermindert wird. The invention provides an adaptive low-pass filter in the signal path, whose parameters depend on the level of the on the digital signal path set digital signal set become. The adaptive low pass filter limits the band digital signal and noise so that the noise power is reduced.

Beispielsweise sind im Signalpfad ein digitaler Signalprozessor und der adaptive Tiefpaß in Reihe geschaltet. Mittels eines Pegelmessers wird der Pegel des digitalen Signals am Ausgang des digitalen Signalprozessors gemessen und in einer Auswerteeinheit ausgewertet, welche das Steuersignal für den adaptiven Tiefpaß erzeugt. For example, there is a digital one in the signal path Signal processor and the adaptive low pass connected in series. through a level meter, the level of the digital signal on Output of the digital signal processor measured and in one Evaluation unit evaluates the control signal for the adaptive low pass.

Die Erfindung wird anhand der Figur näher beschrieben und erläutert. The invention is described in more detail with reference to the figure and explained.

In der Figur ist ein Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung zur Unterdrückung des Rauschens in einem Signalpfad gezeigt. In the figure, an embodiment is one Circuit arrangement according to the invention for suppressing the noise in shown a signal path.

Der Ausgang eines Analog-Digitel-Wandlers AD, an dessen Eingang z. B. ein analoges Audiosignal A liegt, ist mit dem Eingang eines digitalen Signalprozessors verbunden, dessen Ausgang mit dem Eingang eines Pegelmessers P und mit dem Eingang eines adaptiven Tiefpasses TP verbunden ist. Der Ausgang des Pegelmessers P ist mit dem Eingang einer Auswerteeinheit B verbunden, deren Ausgang mit dem Steuereingang des adaptiven Tiefpasses TP verbunden ist. Der Ausgang des adaptiven Tiefpasses TP ist mit dem Eingang eines Digital-Analog-Wandlers DA verbunden, an dessen Ausgang ein weitgehend rauschfreies analoges Audiosignal C abnehmbar ist. The output of an analog-digital converter AD, at its Input z. B. is an analog audio signal A is with Input of a digital signal processor connected, the Output with the input of a level meter P and with the input an adaptive low pass TP is connected. The exit of the Level meter P is connected to the input of an evaluation unit B connected, the output of which is connected to the control input of the adaptive Low pass TP is connected. The output of the adaptive Low pass TP is with the input of a digital-to-analog converter DA connected, at the output of a largely noise-free analog audio signal C is removable.

Der Pegelmesser P ermittelt den Pegel des digitalen Audiosignals am Ausgang des digitalen Signalprozessors DP. Aus diesem Pegel leitet die Auswerteeinheit B ein Steuersignal zur Steuerung des adaptiven Tiefpasses TP ab, der das digitale Audiosignal und auch das Rauschen bandbegrenzt. Die Bandbegrenzung steigt mit abnehmendem Signalpegel. The level meter P determines the level of the digital Audio signal at the output of the digital signal processor DP. For this Level sends the control unit B a control signal Control of the adaptive low-pass TP from the digital Audio signal and also the noise band limited. The band limit increases with decreasing signal level.

Die Erfindung geht dabei von der ersten Erkenntnis aus, daß das Rauschen im Wesentlichen durch den Analog-Digital-Wandler bestimmt wird. Weil das Rauschen eines Analog-Digital-Wandlers verhältnismäßig breitbandig ist, kann es in erster Näherung als weißes Rauschen betrachtet werden. Die Spektralanteile eines Audiosignals, wie z. B. Musik oder Sprache, nehmen dagegen mit wachsender Frequenz ab. Deshalb tritt insbesondere bei kleinen Signalpegeln eine zunehmende Verdeckung der höherfrequenten Nutzsignalanteile durch das Rauschen ein. Der Rauscheindruck nimmt somit beim Hörer entsprechend zu. Durch die erfindungsgemäße Bandbegrenzung im Signalpfad wird nicht nur das Signal, sondern auch das Rauschen bandbegrenzt. Durch die Bandbegrenzung des Rauschens wird die Rauschleistung erheblich reduziert. Weil das menschliche Ohr für niederfrequente Signalanteile empfindlicher ist, wirkt sich eine allmählich einsetzende Bandbegrenzung nicht störend auf den Klangeindruck aus. Die erfindungsgemäße Rauschunterdrückung wirkt umso besser, je größer das Rauschen der Signalquelle, z. B. eines Analog-Digital-Wandlers, gegenüber dem Rauschen der Signalsenke, z. B. eines Digital-Analog-Wandlers, ist. Besonders vorteilhaft läßt sich die Erfindung einsetzen, wenn die Wortlänge der digitalen Signale mindestens zehn Bit beträgt. The invention is based on the first finding that the noise essentially through the analog-to-digital converter is determined. Because the noise of an analog-to-digital converter is relatively broadband, it can in a first approximation can be considered as white noise. The spectral components an audio signal, e.g. B. music or speech, take against it with increasing frequency. Therefore, especially join small signal levels an increasing masking of the higher-frequency useful signal components due to the noise. The The noise impression increases accordingly with the listener. Through the band limitation according to the invention in the signal path is not only the signal, but also the noise band-limited. Through the Band limitation of the noise, the noise power becomes significant reduced. Because the human ear for low frequency Signal components is more sensitive, a gradually affects band limitation does not interfere with the sound impression out. The noise reduction according to the invention works all the more better, the greater the noise of the signal source, e.g. B. one Analog-to-digital converter, compared to the noise of the signal sink, z. B. a digital-to-analog converter. Especially the invention can be used advantageously if the word length of the digital signals is at least ten bits.

Die Erfindung ist allgemein zur Rauschunterdrückung in einem Signalpfad geeignet. Hierzu ist nur ein sehr geringer Aufwand erforderlich, der sich auf den Einsatz eines Pegelmessers, einer Auswerteeinheit und eines adaptiven Tiefpasses beschränkt. The invention is in general for noise reduction in one Suitable signal path. This requires very little effort required, which relies on the use of a level meter, an evaluation unit and an adaptive low-pass filter.

Die Erfindung ist insbesondere für einen in einem Fahrzeug eingebauten Stereorundfunkempfänger geeignet, weil beim mobilen Empfang infolge der Topographie des gerade befahrenen Geländes häufig nur sehr schwache Empfangsfeldstärken zur Verfügung stehen. Die Erfindung ist aber auch für einen stationären Stereorundfunkempfänger geeignet, insbesondere beim Empfang von mit nur schwacher Feldstärke empfangbaren Sendern. Bezugszeichenliste A analoges Audiosignal
AD Analog-Digital-Wandler
B Auswerteeinheit
C rauschfreies analoges Audiosignal
DA Digital-Analog-Wandler
DP digitaler Signalprozessor
P Pegelmesser
TP adaptiver Tiefpaß
The invention is particularly suitable for a stereo broadcast radio receiver installed in a vehicle, because in the case of mobile reception, because of the topography of the terrain being driven on, only very weak reception field strengths are often available. However, the invention is also suitable for a stationary stereo radio receiver, in particular when receiving transmitters which can only be received with a weak field strength. LIST OF REFERENCES A analog audio signal
AD analog-digital converter
B evaluation unit
C noise-free analog audio signal
DA digital-to-analog converter
DP digital signal processor
P level meter
TP adaptive low pass

Claims (9)

1. Verfahren zur Rauschunterdrückung in einem digitalen Signalpfad, dadurch gekennzeichnet, daß aus dem Signalpegel ein Steuersignal zur Steuerung eines im Signalpfad liegenden adaptiven Tiefpasses (TP) abgeleitet wird. 1. A method for noise suppression in a digital signal path, characterized in that a control signal for controlling an adaptive low-pass filter (TP) lying in the signal path is derived from the signal level. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß ein analoges Signal in einem Analog-Digital-Wandler (AD) in ein digitales Signal gewandelt wird, das einem digitalen Signalprozessor (P) zugeführt wird, daß das Ausgangssignal des digitalen Signalprozessors (DP) dem Eingang eines Pegelmessers (P) und dem Eingang des adaptiven Tiefpasses (TP) zugeführt wird, dessen Ausgangssignal dem Eingang eines Digital-Analog-Wandlers (DA) zugeführt wird, und daß das Ausgangssignal des Pegelmessers (P) dem Eingang einer Auswerteeinheit (B) zugeführt wird, die das Steuersignal für den adaptiven Tiefpaß (TP) erzeugt. 2. The method according to claim 1, characterized in that a analog signal in an analog-to-digital converter (AD) in one digital signal is converted to a digital Signal processor (P) is fed that the output signal of the digital signal processor (DP) the input of a Level meter (P) and the input of the adaptive low pass (TP) is supplied, the output signal of the input a digital-to-analog converter (DA) is supplied, and that the output signal of the level meter (P) the input one Evaluation unit (B) is supplied, the control signal generated for the adaptive low-pass filter (TP). 3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Wortlänge des digitalen Signals mindestens zehn Bit beträgt. 3. The method according to claim 1 or 2, characterized in that the Word length of the digital signal is at least ten bits. 4. Verfahren nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, daß als digitales Signal ein digitales Audiosignal vorgesehen wird. 4. The method according to claim 1, 2 or 3, characterized in that as digital signal a digital audio signal is provided. 5. Schaltungsanordnung zur Rauschunterdrückung in einem digitalen Signalpfad, dadurch gekennzeichnet, daß im digitalen Signalpfad ein digitaler Signalprozessor (DP) und ein adaptiver Tiefpaß (TP) in Reihe liegen, daß am Eingang des digitalen Signalprozessors (DP) ein digitales Signal liegt, daß der Ausgang des digitalen Signalprozessors (DP) mit dem Eingang des adaptiven Tiefpasses (TP) und eines Pegelmessers (P) verbunden ist, und daß der Ausgang der Auswerteeinheit (B) mit dem Steuereingang des adaptiven Tiefpasses (TP) verbunden ist. 5. Circuit arrangement for noise reduction in one digital signal path, characterized in that in digital signal path a digital signal processor (DP) and an adaptive low-pass filter (TP) in series that at the entrance the digital signal processor (DP) a digital signal is that the output of the digital signal processor (DP) with the input of the adaptive low pass (TP) and one Level meter (P) is connected, and that the output of the Evaluation unit (B) with the control input of the adaptive Low pass (TP) is connected. 6. Schaltungsanordnung nach Anspruch 5, dadurch gekennzeichnet, daß der Ausgang eines Analog-Digital-Wandlers (AD) an den Eingang des digitalen Signalprozessors (DP) angeschlossen ist. 6. Circuit arrangement according to claim 5, characterized in that the Output of an analog-digital converter (AD) to the input of the digital signal processor (DP) is connected. 7. Schaltungsanordnung nach Anspruch 5 oder 6, dadurch gekennzeichnet, daß der Ausgang des adaptiven Tiefpasses (TP) an den Eingang eines Digital-Analog-Wandlers (DA) angeschlossen ist. 7. Circuit arrangement according to claim 5 or 6, characterized in that the Output of the adaptive low pass (TP) to the input of a Digital-to-analog converter (DA) is connected. 8. Schaltungsanordnung nach Anspruch 5, 6 oder 7, dadurch gekennzeichnet, daß die Wortlänge des digitalen Signals mindestens zehn Bit beträgt. 8. Circuit arrangement according to claim 5, 6 or 7, characterized in that the Word length of the digital signal is at least ten bits. 9. Schaltungsanordnung nach einem der Ansprüche 5-8, dadurch gekennzeichnet, daß es sich bei dem über den Signalpfad übertragenen Signal um ein Audiosignal handelt. 9. Circuit arrangement according to one of claims 5-8, characterized in that it is for the signal transmitted via the signal path by one Audio signal.
DE2002102635 2002-01-24 2002-01-24 Method and circuit for noise reduction Expired - Fee Related DE10202635B4 (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006046188A1 (en) 2004-10-26 2006-05-04 Koninklijke Philips Electronics N.V. Adapting filter to detected interference level
US8929558B2 (en) 2009-09-10 2015-01-06 Dolby International Ab Audio signal of an FM stereo radio receiver by using parametric stereo
US9245516B2 (en) 2012-09-20 2016-01-26 Aisin Seiki Kabushiki Kaisha Noise removal device

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2953346B1 (en) 2009-11-30 2012-08-31 Imra Europ Sas DEVICE FOR REDUCING ELECTROMAGNETIC NOISE IN A VEHICLE

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4322641A (en) * 1979-12-11 1982-03-30 Packburn Electronics Noise reduction system

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4322641A (en) * 1979-12-11 1982-03-30 Packburn Electronics Noise reduction system

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006046188A1 (en) 2004-10-26 2006-05-04 Koninklijke Philips Electronics N.V. Adapting filter to detected interference level
US7791515B2 (en) 2004-10-26 2010-09-07 Nxp B.V. Adapting filter to detected interference level
CN101048940B (en) * 2004-10-26 2013-03-27 Nxp股份有限公司 Adapting filter to detected interference level
US8929558B2 (en) 2009-09-10 2015-01-06 Dolby International Ab Audio signal of an FM stereo radio receiver by using parametric stereo
US9877132B2 (en) 2009-09-10 2018-01-23 Dolby International Ab Audio signal of an FM stereo radio receiver by using parametric stereo
US9245516B2 (en) 2012-09-20 2016-01-26 Aisin Seiki Kabushiki Kaisha Noise removal device

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