JPS60237601A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To maintain the specified input levels to an RFAGC circuit for voice and to provide the improvement in C/N of output and S/N of a reproduced sound signal by detecting the presence or absence of the recording of a video signal and changing over the gains of head amplifiers for voice. CONSTITUTION:A drop-out detecting circuit 59 detects whether the outputs of heads 52, 53 to be used exclusively for video attain a reference level or not and the outputs are made reverse from the previous state if the outputs do not attain the reference level. The output from the circuit 59 is integrated by an LPF 63 and is inputted to a Schmitt circuit 64, from which an H level is outputted in the stage of recording the video signal and an L level is outputted in the stage of non-recording. On the other hand, the gains of the head amplifiers 67, 68 are controlled by the output from the circuit 64 and the gains are decreased by 12dB if there is no video signal as compared to the case when there is the video signal. The input levels to the RFAGC circuit 71 are thus made the same regardless of the presence or absence of the video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording in which a video signal and an audio signal are frequency-modulated and recorded and reproduced on a recording medium using a rotating magnetic head exclusively for video and a rotating magnetic head exclusively for audio, respectively. The present invention relates to a playback device.

Conventional configuration and its problems Figure 1 shows an audio frequency modulation (hereinafter referred to as FM) audio FM of a magnetic recording and reproducing device (hereinafter referred to as VTR) capable of recording and reproducing.
A block diagram of a recording/reproducing circuit is shown.

In FIG. 1, left signal SL and right signal SR of stereo audio signals are supplied to audio input terminals 1 and 2, respectively.

This left signal SL is transmitted to the ACiC circuit 3, the noise reduction circuit 4,
The first FM
Carrier wave 1, 3M) (z = 100) is supplied to modulator 6.
It is FM modulated with a frequency deviation width of about 150 KHz, and the output is passed through a low-pass filter 7 to remove harmonic components, and is input to a mixing circuit 8. Similarly, the right signal SR is AC
iC circuit 9, noise reduction circuit 10. After passing through the pre-emphasis circuit 11 in sequence, the signal is supplied to the second FM modulator 12, where the carrier wave of 1.7 MHz is FM-modulated with a frequency deviation width of about 100 to 150 KHz, and its output is passed through a low-pass filter and then harmonized. The wave components are removed and input to the mixing circuit 8. The FM modulated left signal SL and right signal SR are mixed in a mixing circuit 8, and during recording, the switch 14.16 is set to the recording side (R side), and the output of the mixing circuit 8 is attached to the rotating head cylinder 16. The audio is recorded on a magnetic tape (not shown) by audio magnetic heads 17 and 18 having different azimuth angles. On the other hand, during playback, the playback output from the audio magnetic heads 17 and 18 is switched from the magnetic tape to the switch 14.
A continuous FM modulated audio signal is obtained by alternately switching the switch 22 using the audio-dedicated head switch pulse applied to the control terminal 21 and input to the RFAGC circuit 23. , RF that corrects variations in the output of the audio magnetic head
The output of the AGC circuit 23 is input to the first band pass filter 24, and the FM modulation component of the left signal (carrier wave 1.3MHz
) is extracted and inputted to the first FM demodulator 25, the left signal component is demodulated, and the low-pass filter 26 extracts the audio band (
20 Hz to 20 KHz) is extracted, sequentially passes through a de-emphasis circuit 27 and a noise reduction circuit 28, and is output from a left signal output terminal 29. In addition, the output of the RFAGC circuit 23 is input to the second band pass filter 30,
Only the FM modulation component (carrier wave 1.7 MH2) of the right signal is extracted and input to the second FM demodulator 31, the right signal component is demodulated, and only the audio band is extracted by the low-pass filter 32. In addition, in the VH8 system VTR, the rotating head cylinder has an audio-only magnetic head and a video-only head independently.
On the magnetic tape, an FM modulated audio signal is recorded using a magnetic head dedicated to audio, and an FM modulated video signal is further recorded using a dedicated video head, so a part of the recorded FM modulated audio signal is erased, and only audio is used during playback. The playback output of the magnetic head is significantly (approximately 12
dB) decreases. Therefore, the gain of the head amplifier 19.20 becomes extremely large, and the F
Since there are cases where a magnetic tape on which only M-modulated audio signals are recorded is played back, it is necessary to widen the AGC range of the RFAGC circuit 23.
There are problems in that the /N ratio decreases and the head switch noise width increases.

OBJECTS OF THE INVENTION The present invention is intended to solve these conventional problems, and aims to improve the C/N ratio of the RFAGC output and reduce the head switch noise width when reproducing FM recorded audio signals.

Structure of the Invention The present invention detects the playback output of a video signal, and uses the detected output to switch the gain of the head amplifier of the audio-only head, thereby reproducing a magnetic tape on which a video signal and an audio signal are simultaneously recorded using an RFAGC input level. By making it almost the same when playing back a magnetic tape on which only audio signals are recorded, we have created a VTR capable of recording and playing audio FM with a high C/N ratio in RFAGC output and a narrow head switch noise width. This is what we provide.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Second
The figure shows a block diagram of essential parts of a VTR capable of recording and reproducing audio FM according to the present invention during reproduction. In FIG. 2, a video-dedicated magnetic head 52 provided on a rotary head cylinder 61
．． 63, the video signal output from the magnetic tape (not shown) is amplified by the head amplifier 54.55, and continuous FM modulation is performed by alternately switching the switch 67 using the video dedicated head switch pulse applied to the control terminal 66. A video signal is obtained, and its output is input to an RFAGC circuit 58 and a dropout detection circuit 59.

In the RFAGC circuit 58, the video magnetic head 52.5
Correct the variation in the output of the playback head in step 3. RFAGC
The output of the circuit 58 is input to the FM demodulator 61 via the limiter circuit 60, where the video signal is demodulated and sent to the video output terminal 6.
Output from 2. Further, a dropout detection circuit 69 detects whether the output of the video dedicated head 52, 53 has reached a reference level. If the reference level has not been reached, the output of the dropout detection circuit 59 becomes an output (for example, a Low level) that is opposite to the previous state (for example, if it was a Hi level).

The output of the dropout detection circuit 59 is integrated by a low-pass filter 63, and the output is input to a Schmitt circuit 64, which outputs a digital value. For example, if a video signal is being recorded, output a “Hi” level.
When no video signal is recorded, a "Low" level is output. On the other hand, an audio signal outputted from a magnetic tape (not shown) by an audio magnetic head 65, 66 provided on the rotary head cylinder 61 is amplified by a head amplifier 67, 68 whose gain is variable, and the audio is applied to a control terminal 69. Switch 70 is activated by a dedicated head switch pulse.
A continuous FM modulated audio signal is obtained by alternately switching the FM-modulated audio signal, the output of which is input to the RFAGC circuit 71, corrects variations in the reproduction head output of the audio magnetic heads 65 and 66, and outputs from the output terminal 72. The first and second bandpass filters 24 in FIG. ．． Connect to 30,
The audio signal during playback is obtained from the output terminals 29.35.

The gain of the head amplifiers 67 and 68 in FIG. 2 is controlled by the output of the Schmitt circuit 64, and when there is no video signal, the head amplifier 6
The gain of 7.68 is reduced by about 12 dB. Therefore, R.F.A.
The input level of the GC circuit 71 is almost the same regardless of the presence or absence of the video signal. Effects of the Invention As described above, according to the present invention, the video signal is selectively superimposed on the magnetic tape on which the audio FM signal is recorded. In a recordable/playable VTR, by detecting whether or not a video signal is recorded and switching the gain of the audio head amplifier, the input level of the audio RFAGC circuit can be kept almost constant regardless of whether or not a video signal is being recorded. RFA for audio
The AGC range of the GC circuit can be narrowed, and the audio RF
Since the C/'N ratio in the AGC circuit output is improved and the head switch noise width is narrowed, the S/N of the reproduced audio signal is improved.

[Brief explanation of the drawing]

Figure 1 shows the audio F of a VTR that can record and play back audio FM signals.
FIG. 2 is a block diagram of a main part of an audio FM recording and reproducing circuit of a VTR capable of recording and reproducing audio FM, which is an embodiment of the present invention. 1.2...Input terminal, 3,9...AG
C circuit, 4.10...Noise reduction circuit, 5,11
・・・・・・Pre-emphasis circuit, 6・・・・・・
First FM modulator, 12... Second FM modulator, 7.13... Low pass filter, 8...
...Mixing circuit, 14,15.22...Switch,
16...Rotating head cylinder, 17°18...
...Audio magnetic head, 19.20...
Head amplifier, 21... Control terminal, 23...
... RFAGC circuit, 24 .... First band pass filter, 25 .... First FM demodulator, 3o
...Second bandpass filter, 31...
・Second FM demodulator, 26°32...Low pass filter, 27.33...De-emphasis circuit, 28.34...Noise reduction circuit, 29 ．．
35...Output terminal, 51...Rotating head cylinder, 52.53...Magnetic head for video, 54, 55, 67.68...Head amplifier , 56.69... control terminal, 57. To...
... Switch, 58.71 ... RFAGC circuit, 59 ... Dropout detection circuit, 6o.
...Remisoku circuit, 61...FM demodulator, 62.72...Output terminal, 63...
Low-pass filter, 64...Schmitt circuit,
65.66...Magnetic head for audio only.

Claims (1)

[Claims] An audio signal is frequency-modulated and recorded on a magnetic recording medium using a rotating magnetic head exclusively for audio, and a video signal is frequency-modulated and selectively recorded thereon using a rotating magnetic head exclusively for video. When the audio signal is reproduced and demodulated and the video signal is reproduced and demodulated by the video-dedicated rotary magnetic head, the gain of the reproduction amplifier circuit that amplifies the output of the audio-dedicated rotary head is applied to the reproduction output of the video-dedicated rotary magnetic head. Magnetic recording and reproducing device 0 characterized in that switching is performed by the output of a means for detecting presence/absence.