Claims
- 1. A video tape recorder frequency-modulated audio signal detection system for reproducing both monaural and stereo signals wherein a first indispensible carrier signal modulated by a first audio modulating signal and a second additional carrier signal modulated by a second audio modulating signal is reproduced from a tape, said first indispensible carrier signal modulated by said first audio signal being used for monaural reproduction, comprising:
- first FM demodulator means for demodulating said first indispensible carrier signal and providing a demodulated output including said first audio signal;
- second FM demodulator means for demodulating said second additional carrier signal and providing a demodulated output including said second audio signal;
- detector means for comparing an amplitude of said demodulated output from said second FM demodulator means representing a frequency band above said second audio modulating signal and below undesired components of said second carrier signal with a predetermined value and detecting an existence of said second additional carrier signal in response to said comparison; and
- said detector means comprising a bandpass filter means having its low end selected for removing components within the audio modulating frequency bandwidth of the second audio modulating signal and its high end selected for removing the undesired components associated with the second additional carrier signal in said demodulated output and providing an associated bandpassed output, said band pass filter means being connected to an output of said second FM demodulator means, said bandpassed output of said filter means being connected to a level detector means for converting an output of said filter means into a DC voltage, and an output of said level detector means being connected to a comparator means for comparing the DC voltage to a predetermined value.
- 2. A system according to claim 1 wherein a first bandpass filter means is provided at an input of said first FM demodulator means and a second bandpass filter means is provided at an input to said second FM demodulator means.
- 3. A video tape recorder frequency-modulated audio signal detection system for reproducing both monaural and stereo signals wherein a first indispensible carrier signal modulated by an L+R audio modulating signal and a second additional carrier signal modulated by an L-R audio modulating signal is reproduced from a tape, the L signal being a left channel signal and the R signal being a right channel signal for stereo, and said first indispensible carrier signal modulated by said L+R signal being used for monaural reproduction, comprising:
- first FM demodulator means for demodulating said first indispensible carrier signal and providing a demodulated output including said L+R signal;
- second FM demodulator means for demodulating said second additional carrier signal and providing a demodulated output including said L-R signal;
- detector means having a bandpass filter for comparing an amplitude of said demodulated output from said second FM demodulator means representing a frequency band selected by said bandpass filter above said L-R audio modulating signal and below undesired components of said second carrier signal with a predetermined value and detecting an existence of said second additional carrier signal in response to said comparison, said bandpass filter having an associated bandpassed output; and
- said detector means comprising a level detector means connected to said bandpassed output for converting the demodulated output from said second FM demodulator means into a DC voltage, and an output of said level detector means being connected to a comparator means for comparing the DC voltage to a predetermined value.
Priority Claims (1)
Number |
Date |
Country |
Kind |
1-328914 |
Dec 1989 |
JPX |
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Parent Case Info
This is a continuation of application Ser. No. 08/064,347 filed May 20, 1993, abandoned May 17, 1994, which was a continuation of Ser. No. 07/629,701, filed Dec. 18, 1990, abandoned Jul. 19, 1993.
US Referenced Citations (7)
Foreign Referenced Citations (2)
Number |
Date |
Country |
0066252 |
Aug 1982 |
EPX |
2096435 |
Oct 1982 |
GBX |
Non-Patent Literature Citations (1)
Entry |
Patent Abstracts of Japan vol. 12, No. 474, Dec. 12, 1988. |
Continuations (2)
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Number |
Date |
Country |
Parent |
64347 |
May 1993 |
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Parent |
629701 |
Dec 1990 |
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