Electrical audio signal processing systems and devices – Binaural and stereophonic – Broadcast or multiplex stereo
Patent
1995-02-13
1997-02-25
Kuntz, Curtis
Electrical audio signal processing systems and devices
Binaural and stereophonic
Broadcast or multiplex stereo
381 94, 455306, H04H 500
Patent
active
056066198
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates a circuit arrangement for deriving a signal indicating noise in a received stereo multiplex signal, wherein the stereo multiplex signal is present as a digital signal with a first sampling rate, which is substantially higher than twice the upper limit of the useful frequency range of the stereo multiplex signal.
BACKGROUND INFORMATION
Spectral components above the useful frequency range of a stereo multiplex signal signify noise in the reception of the stereo multiplex signal, which, without further measures, are noticeable as audible noise in the reproduced audio signals. Thus, for example, the ignition spark of an internal combustion engine transmits short high-frequency pulses within a broad frequency range, which results in the aforementioned spectral components in the stereo multiplex signal. Therefore circuit arrangements are known, especially for car radios, which influence the audio signals in a suitable manner depending on the appearance of such spectral components, for example, by sustaining for a short period an amplitude that was present prior to the appearance of the noise.
The object of the present invention is to provide a circuit arrangement, which advantageously obtains those spectral components of the multiplex signal which indicate noise (interference), the requirements of digital signal processing having to be taken into account, in particular--for example a lowest possible requirement for computing power.
SUMMARY OF THE INVENTION
This objective is solved according to the invention in that the received stereo multiplex signal is directed through a low-pass filter, the low-pass-filtered and the received stereo multiplex signal are each subjected to a decimation to a second sampling rate, which is more than twice the upper limit of the useful frequency range of the stereo multiplex signal, and both stereo multiplex signals with the second sampling rate are subtracted from one another.
The circuit arrangement of the present invention has the advantage that the signal indicating noise basically corresponds to the above-described spectral components, but takes up a lower frequency range. Thus, on the one hand, further processing at a lower sampling rate is possible. On the other hand, this signal can be further processed depending on the requirements of the connected circuits, since it contains the basic characteristics of the aforementioned spectral components. Thus, for example, a signal derived with the circuit arrangement of the present invention can control a circuit for temporary storage of the multiplex signal amplitude in order to suppress noise caused by ignition sparks. A signal derived with the circuit arrangement of the present invention can also be used, after suitable further processing via filters and, as the case may be, combination with other signals, for masking the audio signals and for stereo-mono switching.
One improvement of the circuit arrangement of the present invention consists of the low-pass filter having a gradually decreasing frequency response within the useful frequency range. Such a filter is relatively inexpensive and not subject to high quality requirements.
In this improvement of the present invention it is, however, preferably provided that the low-pass filtered stereo multiplex signal passes through a filter at the second sampling rate in order to compensate for the decreasing frequency response of the low-pass filter. Thus, a straight-line frequency response in the useful frequency range is possible in spite of the use of a relatively simple filter.
The circuit arrangement of the present invention is also suited for decimation of the sampling rate of the stereo multiplex signal in the useful frequency range, so that in a further improvement of the present invention, it is provided that the output signal of the filter can be further supplied to a stereo decoder for compensation via a noise suppression circuit.
The circuit arrangement of the present invention can, however, also be configured so that the
REFERENCES:
patent: 5226088 (1993-07-01), Winterer
patent: 5418859 (1995-05-01), Cho
Reich et al., "Digital FM-Stereo Demodulation and Decoding", Signal Processing IV: Theories and Applications, Bd. 2, 8, Sep. 1988, Grenoble, France, pp. 490-502, XP93955.
Bakhru, "Communications Receiver Design Using Digital Processing", Digital Signal Processing, Bd. 2, Nr. 1, Jan. 1992, Orlando, Florida, U.S., pp. 2-13, XP387796.
Chahabadi Djahanyar
Herrmann Matthias
Kaesser Juergen
Vogt Lothar
Blaupunkt-Werke GmbH
Kuntz Curtis
Oh Minsun
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