JPH0678334A - Magnetic recording / reproducing device - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce beat interference that an FM audio signal has on a low-frequency conversion color signal. [Structure] A heterodyne detection circuit 12 and a low-pass filtering circuit 13 detect downbeats from unmodulated left and right channel frequency-modulated audio signals, and the detected downbeats are converted to a frequency close to a flat sync frequency by a frequency dividing circuit 25. Frequency division is performed and the carrier frequency of the right channel is variably controlled by the output of the phase comparator 15 so that the divided output is 90 degrees out of phase with the horizontal synchronizing signal. Is frequency-interleaved with the low-frequency converted color signal to reduce beat interference that the audio signal gives to the color signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus for reducing beat interference that an FM audio signal has on a low-frequency conversion color signal.

[0002]

2. Description of the Related Art Video tape recorders for general household use are
The color under recording method that records the low-frequency conversion color signal in a band lower than the occupied band of the FM luminance signal is adopted.
Regarding audio signals, for example, in the VHS hi-fi system, an audio deep recording system is used in which hi-fi audio is recorded in a deep portion of a magnetic layer of a magnetic tape. The audio deep recording method is a method in which the sound is recorded deep inside the magnetic layer of the magnetic tape by the audio head, and then the video head overwrites with a magnetic field smaller than that, and the audio signal is erased in the deep part of the magnetic tape. It is characterized in that the rest is formed and that a large azimuth difference is provided between the video head and the audio head so that the video signal and the audio signal can be individually taken out during reproduction. As is well known, the VHS hi-fi system employs a two-channel system that uses separate FM carriers for the left and right channels, with a carrier frequency of 1.3 MHz for the left channel and a carrier frequency of 1.7 MHz for the right channel. Is used.

FIG. 3 shows a circuit configuration of an audio recording system of the VHS hi-fi type magnetic recording / reproducing apparatus 1. The audio signals L and R of the left and right channels are voltage controlled oscillators (VCOs) 2 and 3 whose oscillation frequencies are variable according to the applied voltage.
, And each modulates a predetermined FM carrier. The outputs of the voltage-controlled oscillators 2 and 3 are sent to the recording amplifier 4 via the resistors 2r and 3r for level adjustment, line-mixed, and then deep-recorded on the magnetic tape 6 via the voice head 5. Reference numerals 7 and 8 denote phase comparators, which compare the oscillation phases of the voltage controlled oscillators 2 and 3 with the phase reference, respectively, and control the oscillation phases of the corresponding voltage controlled oscillators 2 and 3 so that the phase error becomes zero.

[0004]

Since the conventional magnetic recording / reproducing apparatus 1 adopts the AFM method of frequency-modulating and recording an audio signal, the audio signal of the carrier frequency is generated even when the hi-fi audio is silent. It is recorded on the magnetic tape 6. For this reason, the beat generated between the FM carrier waves of the left and right channels when there is no sound becomes a down beat of 0.4 MHz and an up beat of 3.0 MHz and enters the adjacent band. However, of these beats, the upbeat that can be generated on the high frequency side is erased when the video signal is overwritten after the hi-fi sound,
Downbeats that are created on the low frequency side remain without being erased even by overwriting. As a result, the downbeat of 0.4 MHz adversely affects the band of the low-frequency conversion color signal, and there is a problem in that beat interference is likely to occur in which diagonal beat fringes are generated on the reproduction screen.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a pair of left and right frequency modulations having different carrier frequencies between channels are provided in an intermediate band between the low frequency conversion color signal and the frequency modulation luminance signal. In a magnetic recording / reproducing apparatus for recording an audio signal, a detecting means for detecting a downbeat from the frequency-modulated audio signals of the left and right channels at the time of non-modulation, and an output downbeat of the detecting means are divided into frequencies close to a horizontal synchronizing frequency. A frequency divider circuit and a phase control means for variably controlling the one carrier frequency so that the frequency division output of the frequency divider circuit is out of phase with the horizontal synchronizing signal by approximately 90 degrees. Is.

[0006]

According to the present invention, the downbeat is detected from the frequency-modulated audio signals of the unmodulated left and right channels, the detected downbeat is divided into frequencies close to the horizontal synchronizing frequency, and the divided output is compared with the horizontal synchronizing signal. By variably controlling the carrier frequency of either the left or right channel so that the phase shifts by approximately 90 degrees, the downbeat generated between the left and right channels of the audio signal is frequency interleaved with respect to the low-frequency conversion color signal, and the audio signal is Reduces beat interference on color signals.

[0007]

Embodiments of the present invention will now be described with reference to FIGS.
Will be described with reference to. FIG. 1 is a circuit configuration diagram showing a high-fidelity audio recording system of an embodiment of a magnetic recording / reproducing apparatus of the present invention, and FIG. 2 shows a frequency interleave relationship between a downbeat of an unmodulated FM audio signal and a low frequency conversion color signal. It is a figure for explaining.

The magnetic recording / reproducing apparatus 11 shown in FIG. 1 has an intermediate band between the low frequency conversion color signal C and the frequency modulation luminance signal Y.
The VHS hi-fi system for recording a pair of frequency-modulated audio signals having different carrier frequencies on the left and right channels is adopted, and only the audio recording system is shown here. The heterodyne detection circuit 12 uses the F of the left and right channels when no modulation is performed.
The heterodyne detection circuit 12 detects upbeats and downbeats generated between M audio signals.
A low-pass filter circuit 13 having a required filtering band is connected in order to extract only the downbeat from the output. A 25 divider circuit 14 is connected to the low-pass filter circuit 13, and divides the output downbeat of the heterodyne detection means into a frequency close to the horizontal synchronizing frequency. A phase comparator 15 is connected to the 25 frequency division circuit 14, and the frequency division output and the horizontal synchronizing signal are compared in phase, and an error signal is output based on a phase error of 90 degrees. That is, when the phase error between the downbeat divided by 25 output and the horizontal synchronizing signal is 90 degrees, the output of the phase comparator 15 is zero, but otherwise the phase error 90.
An error signal corresponding to the phase difference is output based on the degree. As mentioned above, the downbeat is 0.4 MHz, and the VHS low-frequency conversion color subcarrier has a center frequency of 40 with the horizontal synchronization frequency fh (= 15.75 kHz).
Since it is set to double frequency (= 629kHz),
As long as the phase error between the downbeat divided by 25 output and the horizontal sync signal is kept at 90 degrees, the downbeat is frequency interleaved with the low-pass converted chrominance signal, as shown in FIG. The output of the phase comparator 15 is the low-pass filtering circuit 16
After being smoothed by, the magnetic recording / reproducing apparatus 11 is sent to a sample hold circuit 17 which performs a sampling operation only for a certain period immediately after the power is turned on. Note that the sampling operation period of the sample hold circuit 17 is limited to a certain period immediately after the power is turned on because the recorded voice is generally silent during this period, and the outputs of the voltage controlled oscillators 2 and 3 are not controlled. This is because there is no doubt that it is an unmodulated FM audio signal.

Further, in the embodiment, the phase of the right channel FM carrier is variably controlled by the output of the phase comparator 15 held in the sample and hold circuit 17. Therefore, the voltage for the right channel sound is generated. A phase correction circuit 18 is interposed between the controlled oscillator 3 and the corresponding phase comparator 8. The phase correction circuit 18 includes the phase comparator 1 sample-held by the sample-hold circuit 17.
5 is a circuit for correcting the output of the phase comparator 8 in accordance with the output of the phase comparator 5.
Heterodyne detection circuit 1 by a signal loop passing through
The phase locked loop 19 from 2 to the sample hold circuit 17 is closed.

In the phase locked loop 19, first, a down beat generated when the FM audio signals of the left and right channels are not modulated is detected. That is, the outputs of the voltage-controlled oscillators 2 and 3 for the left and right channels are the heterodyne detection circuit 12
Detected at 3.0MHz upbeat and 0.4M
Hz downbeat is detected. As described above, the beat frequency component detected by the heterodyne detection circuit 12 is extracted by only the downbeat of 0.4 MHz in the subsequent low-pass filtering circuit 13. The down beat filtered by the low-pass filtering circuit 13 is 1/25 in the 25 frequency dividing circuit 14.
The frequency is divided into 25 frequencies, and here, as a signal of 16 kHz, it is subjected to phase comparison with the horizontal synchronizing signal included in the composite video signal recorded in the video recording system. Since the phase comparator 15 outputs the phase error signal based on the state where the phase of the down beat divided by 25 and the phase of the horizontal sync signal are deviated by 90 degrees, the down beat divided by 25 and the horizontal sync signal are tentatively divided. If the phase is deviated by 90 degrees or more, the phase correction circuit 18 is subjected to the phase correction in the direction of delaying the oscillation phase of the voltage controlled oscillator 3, and the down beat 2 is generated.
The phase error between the divide-by-5 output and the horizontal sync signal is eliminated. On the contrary, when the phase of the down beat divided by 25 and the phase of the horizontal synchronizing signal are deviated from each other by 90 degrees or less, the phase is shifted in the direction of advancing the oscillation phase of the voltage controlled oscillator 3 with respect to the phase correction circuit 18. Corrected and downbeat 25
The phase error between the divided output and the horizontal sync signal is eliminated.

As described above, according to the magnetic recording / reproducing apparatus 11, the downbeats of the left and right channel audio signals obtained by modulating FM carrier waves having different frequencies are divided, and this is divided into 90 horizontal synchronizing signals included in the composite video signal. Since the frequency carrier of the right channel FM carrier is frequency-shifted so that the phase shifts, the left channel audio signal FM-modulated by the 1.3 MHz audio carrier and the F carrier by the 1.7 MHz audio carrier.
M.I. generated between the M-modulated right channel audio signal and 0.
Even if the 4 MHz downbeat jumps into the occupied band of the low-frequency conversion color signal, this downbeat can be frequency-interleaved with the low-frequency conversion color signal, thereby recording no audio, that is, an unmodulated FM audio signal. At this time, the downbeat caused by the frequency difference between the left and right audio carrier waves does not cause beat interference with respect to the low-frequency conversion color signal, and it is possible to reduce the oblique beat interference that occurs on the reproduction screen.

When voice is present instead of no voice, the downbeats generated between the FM audio signals of the left and right channels also fluctuate randomly, so the beat interference itself also fluctuates momentarily on the reproduction screen. The visual effect is smaller than when there is no sound in which beat interference is fixed. For this reason, it is possible to appeal a sufficient image quality improving effect only by the beat interference countermeasure when there is no sound. Further, in the above-described embodiment, the phase correction circuit 18 may be provided between the voltage controlled oscillator 2 for the left channel, not the right channel, and the corresponding phase comparator 7.

[0013]

As described above, according to the present invention, the downbeats of the left and right channel audio signals obtained by modulating FM carrier waves having different frequencies are frequency-divided, and the phase is shifted by 90 degrees with respect to the horizontal synchronizing signal. Since the frequency control is applied to one FM carrier, in the case of the VHS hi-fi system, a left channel audio signal FM-modulated by a 1.3 MHz audio carrier and an FM carrier by a 1.7 MHz audio carrier are used.
0.4 generated between modulated right channel audio signal
Due to the frequency interleaving with the luminance signal, the center frequency of the MHz downbeat is 40 times the horizontal sync frequency (=
The frequency of the low-frequency conversion color subcarrier selected to 629 kHz) is frequency-interleaved so that the downbeat is frequency-divided into 25 and the horizontal synchronizing signal (= 15.7).
The phase control may be performed so that the phase error of 5 kHz) is maintained at about 90 degrees.
When the M audio signal is recorded, the beat interference caused by the downbeat caused by the frequency difference between the left and right audio carrier waves on the low-frequency conversion color signal is suppressed, and the beat interference generated diagonally on the reproduction screen is improved. It has excellent effects such as reduction.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a high-fidelity audio recording system of an embodiment of a magnetic recording / reproducing apparatus of the present invention.

FIG. 2 is a diagram for explaining a frequency interleave relationship between a downbeat of an unmodulated FM audio signal and a low-frequency conversion color signal.

FIG. 3 is a circuit configuration diagram showing a high-fidelity audio recording system as an example of a conventional magnetic recording / reproducing apparatus.

[Explanation of symbols]

 2, 3 Voltage-controlled oscillator 7, 8 Phase comparator 11 Magnetic recording / reproducing device 12 Detection means (heterodyne detector) 13 Low-pass filtering circuit 14 25 Dividing circuit 15 Phase control means (phase comparator) 18 Phase correction circuit 19 Phase Locked loop

Claims (1)

[Claims] 1. A magnetic recording / reproducing apparatus for recording a pair of left and right frequency-modulated audio signals having different carrier frequencies between channels in an intermediate band between a low-frequency converted color signal and a frequency-modulated luminance signal, wherein the left and right channels are not modulated. Detecting means for detecting a down beat from the frequency-modulated audio signal of, a frequency dividing circuit for dividing the output down beat of the detecting means to a frequency close to the horizontal synchronizing frequency, and a frequency division output of the frequency dividing circuit is a horizontal synchronizing signal. About 90 degrees out of phase,
A magnetic recording / reproducing apparatus comprising: a phase control unit that variably controls the one carrier frequency.