JPH0260385A - Audio noise eliminating device for video tape recorder - Google Patents

Abstract

PURPOSE:To reduce the switching noise by detecting the phase deviation between channels and correcting the variance of the time base of a signal in an audio processing path based the detection result. CONSTITUTION:Phase comparators 68 and 78 compare phases of inputted reproduced signals with the phase of the reference signal from a reference signal generator 40 to detect phase errors. Detected error signals are given to frequency control terminals of VCOs 69 and 79, and oscillation outputs are used as driving signals of time base correcting circuits 63 and 73. Transfer speeds of circuits 63 and 73 are controlled in accordance with frequencies of driving signals. As the result, the variation of the phase of an FM audio signal is detected by comparators 68 and 78 though the phase of the FM audio signal is varied, and the variance of the time base is cancelled in the signal inputted to an FM demodulating part. Consequently, the continuity is improved and the switching noise for demodulation of the audio signal is reduced.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to recording video and audio signal information on a magnetic tape and to reproducing the recorded signals using a helical scan method. The present invention relates to an audio noise removal device for a video tape recorder.

(Conventional technology) Conventionally, HiFi technology has enabled high-quality audio signal recording and playback.
In a video tape recorder (hereinafter referred to as a VTR), video information and audio information are recorded on the same track by helical scanning and are then played back.

Broadly speaking, there are two methods for recording video information and audio information on the same track using helical scanning.

The first method, like the VH3Hi Fi VTR, is a method in which video signals and audio signal information are recorded in the surface layer and the deep layer using rotary heads with different gap lengths. The second method is a method in which video signals and audio signal information are frequency-modulated so that their frequency deviation widths do not overlap and are recorded using the same rotary head, like a β Hi Fi VTR.

In addition, in the above-mentioned VTR, in order to prevent audio short-circuiting due to helical scanning, a period is provided in which the time axes of the signals overlap due to the relationship between the rotation loci of the pair of rotating heads and the arrangement of the magnetic tape. The paired rotating heads are alternately switched for reproduction. Therefore, the playback output from the paired rotating heads is
There is an overlapping period, and in order to perform signal processing, a switch control means is required to change the switch to select one of the two during this period so that the reproduced audio signal becomes a smooth continuous signal.

Conventionally, a noise removal circuit has been used to make audio signals continuous. This is because even if the rotating head is switched within the above period, the carrier of the FM audio signal does not necessarily continue smoothly between the outputs of each head, and the audio signal after demodulation contains spike noise. This is because there are many. Methods for removing such noise include the O approximation method, which holds the value immediately before the noise is included and interpolates it into the noise period, or the linear approximation method, which predicts the noise period according to the signal slope immediately before the noise and interpolates it. etc.

FIGS. 4 and 5 are signal diagrams for explaining the operation of the noise removal circuit in the VH5Hi Fi VTR.

1 on the diameter of the rotating drum in the VTR playback mode.
Two rotary heads for audio signals (A channel, B channel) located opposite each other at 80 degrees are alternately switched to obtain two outputs. The FM audio signals from each rotary head ((a) to (d) in the same figure) have an overlapping period, but due to differences in tape tension during recording and playback, etc. ).

When such a signal is switched by a head switching pulse (see (e) in the same figure) during the overlap period, a discontinuous portion occurs in the FM signal as shown in (f) in the same figure. When this signal is FM demodulated, so-called switching noise, which is large-amplitude spike noise, occurs as shown in FIG.

FIG. 5 shows a signal waveform diagram for explaining the operation of the interpolation circuit for removing the switching noise. This example is a previous value hold method, in which the level immediately before the noise is held and interpolated during the period of switching noise occurring in the demodulated audio signal. In other words, the waveform shown in FIG. 3(a) becomes a waveform from which noise has been removed, as shown in FIG. 2(b).

However, when considering the difference in tape tension during recording and playback, the difference in tension caused by the difference in the tape position relative to the cylinder during playback, and the compatibility, the installation of opposing rotating heads is difficult due to angular division errors, etc. The phase difference is relatively large, and when the FM signals from each head are demodulated and connected, the phase of the audio signal itself becomes discontinuous, resulting in skew distortion as shown in FIGS. 5(c) and 5(d).

(Problem to be solved by the invention) As mentioned above, in the conventional speech noise removal device,
■ Differences in tape tension during recording and playback; ■ Differences in tension resulting from differences in tape position relative to the cylinder during playback; The phase difference of the FM audio signal is relatively large, and even if the noise portion is interpolated after demodulation, it is difficult to correct even the skew distortion.

Therefore, the present invention is capable of detecting a wide range of phase shifts (time axis fluctuations) between channels during the overlap period of the reproduced signal, and corrects the time axis fluctuations of the signal in the audio signal processing path based on this detection result. An object of the present invention is to provide an audio noise removal device for a video tape recorder that can further improve switching noise reduction effects.

[Structure of the invention] (Means for solving the problem) This invention adds a frequency signal of 2fH, which is twice the frequency of a video horizontal synchronizing signal, which is a frequency signal outside the audible frequency band, to an audio signal. is FM modulated and recorded, and at the time of playback, the reproduced 2f11 signal and the standard 2f
The configuration is such that a phase error is detected by comparing the signal with the H signal, and the time axis of the signal in the audio signal reproduction processing path is shifted and controlled in accordance with the error detection signal.

Furthermore, the present invention configures a rotary head for video signals for surface recording and a rotary head for audio signals for deep recording as an integrated head with a double azimuth configuration, so that the rotary head for video signals and for audio signals can be used as an integrated head with a double azimuth configuration. The skew distortion of the audio signal is detected by attaching the rotary heads separately to eliminate factors that would cause angle division errors between the two, and by detecting the phase fluctuation of the reproduced video horizontal synchronization signal. The configuration is such that the time axis of the signal in the audio signal reproduction processing path is corrected based on the result.

(Function) By the above means, the time axis fluctuations of the information regarding the audio signal are detected and corrected with high accuracy as a whole, and the continuity is improved, so that the switching noise when demodulating the audio signal is greatly reduced. Therefore, it is possible to perform good interpolation processing for the noise portion at the time of head switching.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The left channel signal Lch of the audio signal for recording is input to an input terminal 11, a low-pass filter 12. Noise reduction circuit 13. The signals are sequentially processed by an emphasis circuit 14 and converted into an FM audio signal by an FM modulator 15.

On the other hand, the right channel signal Rch of the recording audio signal is input to the input terminal 16. Low pass filter 17. The signal is input to the adder 19 via the noise reduction circuit 18.

In this adder 19, the 2fH(f)l is the horizontal synchronizing signal frequency) signal from the reference signal generator 40 is added to the right channel signal Rch, and the output of this adder 19 is processed by an emphasis circuit 20 and subjected to FM modulation. The signal is input to the device 21. The carrier frequency of this FM modulator 21 is a different frequency from the carrier frequency of the previous FM modulator 15.

The signals from FM modulators 15 and 21 are combined in adder 22, and the summed output is sent to recording amplifier 23. Audio head 52a via switch 24.

52b. The switch 24 is controlled by the recording/playback switching signal (RPC/PLAY) supplied from the terminal 25, and in the recording mode guides the output of the recording amplifier 23 to the audio heads 52a', 52b.

The audio heads 52a and 52b are attached as a pair at 180° opposing positions on the periphery of the rotating drum 50.
Further, the rotating drum 50 includes audio heads 52a and 52b.
A pair of image heads 51a and 51b are mounted at opposite positions of 180° perpendicular to the diameter connecting the two.

A video signal for recording is input to a recording video signal processing circuit 32 via an input terminal 31 and converted into a recording video signal. This recorded video signal is supplied to the video heads 51a and 51b via the switch 33. Switch 33 is also terminal 3
The recording/reproduction switching signal (RFC/PLY
), and in the recording mode, the output of the recorded video signal processing circuit 32 is controlled by the video heads 51a and 51b.
lead to.

Next, the signal path when the VTR is in the playback mode will be explained.

The FM audio signal from the audio head 52a is transmitted to the regenerative amplifier 6.
1 and input to the time axis correction circuit 63 via the low-pass filter 62. In this time axis correction circuit 63, a time axis shift is performed based on a time axis error signal, which will be described later.
Time axis correction of audio information is performed. Similarly, the FM audio signal from the audio head 52b is amplified by the regenerative amplifier 71 and input to the time axis correction circuit 73 via the low-pass filter 72. This time axis correction circuit 73 also performs a time axis shift based on a time axis error signal, which will be described later, and performs time axis correction of audio information.

The output of the time axis correction circuit 63 is supplied to a bandpass filter 64 for the right channel and a bandpass filter 81 for the left channel. The output of the bandpass filter 64 converts the right channel to F.
The demodulated signal is supplied to an FM demodulator 65 that performs M demodulation, and the demodulated signal is supplied to a bandpass filter 67 and one of the switches I (Sl) via a de-emphasis circuit 66.The output of the bandpass filter 81 converts the left channel into FM FM to demodulate
The demodulated signal is supplied to a demodulator 82, and the demodulated signal is supplied to one of the switches H82 via a de-emphasis circuit 83.

On the other hand, the output of the time axis correction circuit 73 is also transmitted by the band filter 74 for the left channel and the band filter 91 for the right channel.
supplied to The output of the bandpass filter 74 is supplied to an FM demodulator 75 for FM demodulating the left channel, and the demodulated signal is supplied via a de-emphasis circuit 76 to the bandpass filter 77 and the other switch H8I. Further, the output of the bandpass filter 91 is supplied to an FM demodulator 92 that performs FM demodulation of the left channel, and the demodulated signal is supplied to the other switch H32 via a de-emphasis circuit 93.

Switches H3I and H32 are controlled by a head switching pulse (SWP) supplied to a terminal 102 via a delay circuit 103, and select the head output while tracing a track on the magnetic tape. These are switches for leading to a right channel signal processing section and a left channel signal processing section, respectively. Since the head switching pulse (SWP) is set to the switching timing of the video heads 51a and 51b, it is adjusted to match the switching timing of the audio heads 52a and 52b through the delay circuit 103 and is supplied to the switches H8I and H82. Ru. The right channel signal processing section includes a noise interpolation circuit IR, a noise reduction circuit 2R, and a low-pass filter 3R (removes components outside the audible frequency band), and a reproduced right channel audio signal is derived from a terminal 4R. The left channel signal processing section includes a noise interpolation circuit IL, a noise reduction circuit 2L, and a low-pass filter 3L (removes components outside the audible frequency band), and a reproduced right channel audio signal is derived from a terminal 4L.

The noise interpolation circuits IR and IL are circuits that perform the same processing as the interpolation described in FIGS. 4 and 5, and smooth the signal portion at the switching point between the two heads.

Note that the playback video information is based on the head switching pulse (SWP).
The video signal is input to the reproduced video signal processing circuit 100 via a switch H83 controlled by a switch H83, converted into an original video signal, and then output to an output terminal 101.

Next, in addition to noise interpolation, the noise reduction device according to the present invention is provided with means for detecting and correcting a time axis error in information regarding an audio signal.

That is, the bandpass filter 67.77 extracts the 2f11 signal added to the audio signal during recording, and the reproduced 2fH signal from each filter is supplied to the phase comparator 68.78. . The phase comparators 68 and 78 receive the input reproduced 2fH signal,
A phase comparison is performed with the reference 2fH signal from the reference signal generator 40 to detect a phase error. Each phase comparator 68.
The error signals detected at 78 are applied to frequency control terminals of voltage controlled oscillators 69 and 79, respectively. and,
The oscillation outputs of the voltage controlled oscillators 69 and 79 are used as drive signals for the time axis correction circuits 63 and 73, respectively. The time axis correction circuits 63 and 73 are analog delay circuits using, for example, a CCD, and the transfer speed is controlled according to the frequency of the drive signal. A memory may be used as the time axis correction circuit. As a result, even if a phase variation occurs in the FM audio signal, the variation is detected by the phase comparators 68 and 78, and the signal input to the FM demodulation section is treated as having the previous time axis variation canceled. Furthermore, the two systems of signals are also phase-aligned.

In this embodiment, the fH multiplied signal of the reference signal generator 40 is not used only for time axis fluctuation correction of the audio signal as described above, but is derived via the output terminal 41 and is output from the rotating drum 50. It is also used as a synchronization reference signal in a servo circuit (not shown).

As explained above, according to this embodiment, in a VTR in which audio signal information is recorded alternately with two rotary heads, differences in tape tension during recording and playback, and ■differences in tape position relative to the cylinder during playback occur. Differences in tension, ■When considering compatibility,
The mounting of opposing rotary heads makes it possible to compensate for phase differences in FM audio signals between channels due to angular division errors through time axis correction, thereby obtaining continuous reproduced audio signals without skew distortion. Due to this time axis correction, switching noise at the signal joint in the head switching section is also reduced to a greater extent than before, but by performing interpolation at this portion, a reproduced audio signal of even higher quality can be obtained.

In the above embodiment, when time axis correction was performed, it was performed at the FM audio signal stage. However, the present invention is not limited to this, and it may be performed after FM demodulating the audio signal and before performing noise interpolation. Further, in the above embodiment, a signal processing path for recording and reproducing a stereo audio signal was shown, but it goes without saying that the present invention can also be applied to a path for recording and reproducing a monaural signal.

Furthermore, in the above embodiment, an example was shown in which the video signal information is recorded on the surface and the audio signal information is recorded on the deep layer. Of course, the present invention can also be applied to a VTR in which both signal information is recorded and reproduced using the same rotary head so that they do not overlap. In the case of such a VTR, since the rotary head for recording and reproducing video and audio signal information on the tape 55 is shared, the number of heads is reduced to 1/2 of that in the above embodiment. Furthermore, the delay circuit 103 is also unnecessary.

FIG. 2 shows another embodiment of the invention, and FIG. 3 shows the second embodiment.
An example of a rotary head device used in the VTR shown in the figure is shown.

First, the basic configuration of the rotary head device shown in FIG. 3 will be explained. Head bases 111 and 115 are attached to 180° opposing positions of the rotating drum 110, and a standard video head 112 and an audio head 113 with a double azimuth structure are attached to the head base 11. A standard video head 115 and audio head 116 having a double azimuth structure are attached to the base 114.

This rotary head device 110 is equipped with the above-mentioned Radbase 111.1 so as to be able to support playback at triple speed (EP).
The head base 117.1 is located at a position perpendicular to the head base 117.1.
20 is installed. A video head 118 and an audio head 119 are attached to the head base 117, and a video head 121 and an audio head 12 are attached to the head base 120.
2 is installed.

The VTR shown in FIG. 2 will be explained. The video signal information reproduced from the video heads 112 and 115 is transferred to the switch 130.
is supplied to one input terminal and the other input terminal. This switch 1
30 is a head switching pulse (
SνP) to select the head output while tracing the magnetic tape, and to select the output of the head that is tracing the magnetic tape.
to be introduced.

The video signal restored by the reproduced video signal processing circuit 131 is
It is led out to the output terminal 132. The reproduced video signal is also supplied to a horizontal synchronization separation circuit 133.

The horizontal synchronization separation circuit 133 separates the horizontal synchronization signal and supplies it to the phase comparator 134. The phase comparator 134 performs a phase comparison between the reproduced horizontal synchronizing signal and the horizontal frequency reference signal from the reference signal generator 135, and derives an error signal. This error signal is applied to voltage controlled oscillators 137 and 1
38 frequency control terminals to control the oscillation frequency of each oscillator. As a result, voltage controlled oscillators 137 and 1
The oscillation frequency of 38 is controlled according to the phase fluctuation of the reproduced horizontal synchronization signal. Voltage controlled oscillator 137 and 1
The oscillation output of 38 is transmitted to a time axis correction circuit 153 and 1
It is used as a drive signal for 56.

On the other hand, audio signal information reproduced by audio heads 113 and 116 is amplified by amplifiers 151 and 154, respectively, and then supplied to low-pass filters 152 and 155. The audio signal information derived from the low-pass filter 152.15.5 (F
M audio signals) are sent to time axis correction circuits 153 and 15, respectively.
6.

FM time axis corrected by time axis correction circuits 153 and 156
The audio signals are supplied to one and the other terminals of switch 157, respectively. This switch] 57 is the delay circuit 1
Head switching pulse (SWP) supplied through 81
The head output during tracing of the magnetic tape is selected and supplied to the left channel audio signal processing section and the right channel audio signal processing section.

The audio signal processing section for the left channel has a bandpass filter of 1.6
1. FM demodulator 162. De-emphasis circuit 163.
Noise interpolation circuit 164, noise reduction circuit 165
, and a low-pass filter 166, and outputs a left channel audio signal from a terminal 167. The right channel audio signal processing section also includes a bandpass filter 171. FM demodulator 172.
De-emphasis circuit 173. noise interpolation circuit 174,
It is composed of a noise reduction circuit 175 and a low-pass filter 176, and outputs a left channel audio signal from a terminal 177.

This embodiment is constructed as described above, and in particular, the video head and audio head are constructed as a double azimuth structure. For this reason, monitoring the phase of the horizontal synchronization signal separated from the video signal directly leads to monitoring the phase shift of the audio information. Therefore, by using the phase error information of the reproduced horizontal synchronization signal to correct time axis fluctuations in the audio signal processing path, it is possible to obtain a stable reproduced audio signal, and moreover, it is possible to obtain a stable reproduced audio signal. Phase shift can be reduced. Furthermore, since the rotary head has a double azimuth configuration, the angular division error between the video head set and the audio head set mounted on the rotary drum is greater than when the set of video heads and the set of audio heads are installed at different central angle positions. can be reduced. If the video head set and the audio head set are installed at different center angle positions, and an angle division error occurs, even if the horizontal synchronization signal is obtained in normal phase, the paired audio FM between heads
Problems such as a large phase shift in the audio signal and deterioration of VTR compatibility occur, but such problems can be reduced by adopting the double azimuth configuration in which the video head and the audio head are integrated as described above. be able to.

In the above embodiment as well, the time axis fluctuation is corrected over the entire audio signal, and it is possible to eliminate the phase shift between the outputs of the paired audio heads. As explained in FIG.
This is to obtain a high-quality reproduced audio signal.

[Effects of the Invention] As explained above, the present invention is capable of detecting reproduced signals derived from multiple heads and a wide range of phase shifts between the reproduced signals, correcting this and stabilizing it, and reducing switching noise. The effect can be made even better.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the invention, FIG. 2 is a block diagram showing another embodiment of the invention, and FIG. 3 is an explanatory diagram showing an example of the configuration of the rotary head device shown in FIG. FIG. 4 is a diagram illustrating the progress of switching noise generation due to head switching, and FIG. 5 is a waveform diagram illustrating interpolation processing for removing switching noise. 50.110 = Rotating drum, 51a, 51b. 11.2, 115, 118, 121... video head,
52a, 52b, 113, 116, 119°122...
・Audio head, 3R, 3L, 12.17°62.72,
152,155,166.176...Low pass filter,
2R, 2L, 13, 18, 165° 175... Noise reduction circuit, 14.20... Emphasis circuit, 15.21... FM modulator, 19.22... Adder, 24.3B, H8I~H83,157...Switch, 63.73,153°156...Time axis correction circuit, 64,67.74°77.81,91,161,17
1... Bandwidth filter, 65, 75, 82, 92, 16
2,172...FM demodulator, 66.76.8B, 93
．． 163173...De-emphasis circuit, 68,7
8゜134...Phase comparator, 69,79.137138
...Voltage controlled oscillator, 40,135... Reference signal generator, IR, IL, 164,174... Noise interpolation circuit, 100,131... Playback video signal processing circuit, 13
3...Horizontal synchronization separation circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (4)

[Claims] (1) Each frequency modulated signal obtained by frequency modulating a carrier wave of a predetermined frequency with a video signal and an audio signal, respectively, is supplied to a pair of rotating heads facing each other on the diameter of a rotating drum. Due to the relationship between the rotation locus of the rotary head and the arrangement of the magnetic tape, the paired rotary heads are alternately switched during the period in which the time axes of the signals overlap, and the video signal and the video signal are rotated diagonally with respect to the running direction on the magnetic tape. In a helical scan video tape recorder having means for multiplex recording the frequency modulated signal with an audio signal using the rotary head, and means for reproducing the recorded signal, a reference signal generating means for generating a reference signal, and during recording, the audio signal for recording is supplied, the audio signal is band-limited and the reference signal is added to the audio signal, and the audio signal with the reference signal is used to generate the predetermined frequency. means for frequency modulating a carrier wave of the carrier wave and recording it on the magnetic tape; demodulating means for receiving a frequency modulated signal, which is audio signal information from the rotary head, at the time of reproduction to obtain an audio signal with a reproduction reference signal; a time axis correction means provided either before or after the means; a filter means for extracting a reproduction reference signal from a demodulated signal from the demodulation means; a reproduction reference signal from the filter means and the reference signal; The oscillation frequency is controlled based on the phase comparison means for detecting the phase error with the reference signal from the generation means, and the error signal from the phase error detection means, and the oscillation output drives the time axis correction means. 1. An audio noise removal device for a video tape recorder, comprising: oscillation means for controlling the time axis of a signal passing through the correction means. (2) The paired rotary heads frequency-modulate the carrier wave of a predetermined frequency with the first frequency modulation signal obtained by frequency modulating the carrier wave of a predetermined frequency with the audio signal with the reference signal and the video signal. and is connected to a recording modulation means for obtaining a second frequency modulation signal that is modulated so that the frequency shift width does not overlap with the first frequency modulation signal. An audio noise removal device for a video tape recorder according to item 1. (3) The paired rotating heads include a first set of rotating heads for recording and reproducing frequency modulated signals based on video signals, and a second set of rotating heads for recording and reproducing frequency modulated signals based on audio signals. 2. The audio noise removal method for a video tape recorder according to claim 1, wherein the first and second sets of rotary heads have different recording characteristics in the direction of the thickness of the magnetic layer of the magnetic tape. Device. (4) Frequency-modulated signals obtained by frequency-modulating carrier waves of predetermined frequencies with video signals and audio signals, respectively, are supplied to each pair of rotating heads facing each other on the diameter of the rotating drum. The rotating heads between the pairs have different gap lengths, and due to the relationship between the rotation loci of the paired rotating heads and the arrangement of the magnetic tape, the paired rotating heads alternately switch during periods when the time axes of the signals overlap. is,
The magnetic tape has means for recording the frequency modulated signal based on the video signal and the audio signal in multiple layers in a surface layer and a deep layer obliquely with respect to the running direction on the magnetic tape, and means for reproducing the recorded signal. In the helical scan type video tape recorder, the rotary head for recording each frequency modulated signal based on the video signal and the audio signal on the magnetic tape includes a pair of one side for the video signal and one for the audio signal. A head means having a double azimuth configuration provided at substantially the same location on the rotating drum and having a similar double azimuth configuration on the other side, and a horizontal synchronizing signal from a demodulated signal of video information reproduced from the rotating head for the video signal. a synchronization separation means for separating; a phase error detection means for detecting a phase error by comparing the phases of the horizontal synchronization signal from the synchronization separation means and the horizontal frequency signal from the reference signal generation means; and a rotary head for the audio signal. and a time axis correction means provided in the middle of a signal path for processing the reproduction output from the phase error detection means for shifting and controlling the time axis of the reproduction output according to the error detection signal from the phase error detection means. Audio noise removal device for video tape recorders.