JPS6087407A - Sound tracking correction circuit of magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To secure the interchangeability among magnetic tapes and VTR devices by providing an external control means, a correction signal wave generating means and a correction means to a reproduction circuit system and correcting the level differential of the DC of the FM demodulation output produced in a head switching mode. CONSTITUTION:When a tape recorded by another VTR is reproduced, the DC level differs before and after a head switching mode. Thus the DC contains buzz noises if it is delivered as it is to a line-out terminal. In this respect, a sawtooth wave synchronous with the head switch timing is produced by a correction wave generating circuit 3. Then a variablb resistor VR is used to change the correction amount of the inclination of the sawtooth wave to obtain a corrected waveform which can eliminate the DC level difference. As a result, an off-center correcting circuit 2 has an output containing no DC level differential with reduced buzz noises. Thus an optimum off-center correction amount is given to each recording tape from outside in a reproduction mode despite the difference of off- center amounts of the VTR used for recording. Thus it is possible to obtain satisfactory reproduced sounds.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a magnetic recording and reproducing device that records audio signals using a rotating head using FM (frequency modulation), and when reproducing audio signals recorded by another device, The relative speeds of the rotary head and recording tape do not match during playback due to the misalignment of the axial center of the upper cylinder of the rotary head (hereinafter referred to as off-center amount) between the two devices, and this is demodulated as a buzz sound when switching heads. The present invention relates to an audio tracking correction circuit for a magnetic recording/reproducing device in which the noise is corrected by an external adjusting means.

[Technical background of the invention and its problems] Conventionally, in a video tape recorder (hereinafter referred to as a VTR), audio is recorded on an audio track at the end of the tape.
It was recorded using the AC bias recording method. In this case, as video signals are recorded at high density, the tape speed is reduced, and in recent years, sound quality with poor frequency characteristics has been recorded and reproduced, especially in long-time mode. For this reason, recently, by recording audio signals with FM modulation using a rotating head,
A method has now appeared that dramatically improves the audio output characteristics of a VTR without being influenced too much by tape speed. This method is characterized by the ability to obtain high quality sound that cannot be obtained with conventional AC bias recording. Even when a tape is recorded on a VTR, it is necessary to reproduce high-quality audio during playback.

However, in reality, there are various variations between VTRs, including misalignment of the axis center of the upper cylinder of the rotating cylinder, and when recording and playing back with the same VTR, the rotating head and the The relative speed with the tape perfectly matches, but it does not match perfectly with the recording tapes sold and other VTRs, and in particular, the relative speed at the beginning and end of writing of the head changes separately due to differences in the off-center node. , appears as a step difference in the DC level during FM demodulation. As a result, when a tape recorded in the above manner is played back, it is played back as a buzz sound, and there is a problem in that it is not possible to hear high-quality audio.

Next, a case where the above phenomenon occurs will be explained in detail.

As shown in FIG. 1, the starting point of the head is point A, the end of writing is point B, and the line connecting points A and B is the X axis. Let R be a rotating cylinder, its true center is 0+ (0, O), and its actual center is 02 (X, V). Also, O+ (0
, 0) and is perpendicular to the X-axis as the y-axis. When considering the speed of the head at points A and B, the deviation in the direction (2) has almost no effect, so consider replacing it with 0s (X, 0). If the radius of the rotating cylinder R is ``, and the angular velocity of the head is ω, then the head speed at each point of the VTR without an off-center bottle [center 0+(0,0)] is 1J6
is V, = r ・ω = constant. In addition, the speed ue- of the head at each point of the actual VTR [center 03 (X, 0)] is ``tbt-=re ・ω'', where r is the diameter from the center o3 to the head.In this case, , the speed of the head at points A and B is
At point A,:o=(r−x)・0 At point 8, t/:e=(r×x)@ω. Therefore, the speed ratio with respect to the case where there is no off-center amount is t/,;, /1te=(r −x )/r.

Photograph t7/Atsushi=(r +X)/r. Incidentally, when a tape recorded with a VTR without an off-center node is played back, the change in playback frequency is proportional to the speed ratio. Therefore, if the frequency at the time of recording is the frequency at the time of reproduction, at point A, the frequency at point A is ((r − When this is subjected to FM modulation, as shown in FIG. 2, there is a step difference in the DC level between points A and B when switching heads, which is reproduced as a buzz sound.

[Objective of the Invention 1] In view of the above-mentioned points, the present invention corrects the difference in DC level that occurs when switching heads when performing FM modulation when playing back from a tape recorded with FM on another VTR, and eliminates buzz noise. It is possible to prevent this from being reproduced as such, and to correct the level difference in the demodulated DC level, it is possible for general users to arbitrarily adjust the amount of correction using an external adjustment means of the VTR set. Even if the off-center amount differs depending on the VTR set used, the V used for recording during playback
An object of the present invention is to provide an audio tracking correction circuit for a magnetic recording/reproducing device that can easily change the amount of correction depending on the TR set.

[Summary of the Invention] The audio tracking correction circuit of the magnetic recording/reproducing device of the present invention is a magnetic recording/reproducing device configured to record and reproduce audio signals on a magnetic tape by FM modulation using a rotary head. FMtl that occurs when switching heads! a correction means for correcting a step difference in the DC level of the II output; a correction wave signal generating means for generating a correction wave signal synchronized with the head switching timing and supplying the correction wave signal to the correction means; and a correction wave signal generating means for the correction wave signal generation means. The device is connected to an external adjustment means that can adjust the amount of correction by adjusting the correction waveform from outside the device, and corrects the DC step difference mainly caused by the amount of off-center. , to reduce or eliminate buzzing noise when switching heads.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 3 is a block diagram showing a first embodiment of the audio tracking correction circuit of the magnetic recording/reproducing apparatus according to the present invention, and FIG. 4 is an explanatory diagram of its operation.

In Fig. 3, reference numeral 1 is an FM demodulator, which uses a rotary head to alternately reproduce FM-recorded audio signals from a tape through a head selector switch, inputs the reproduced signal, and outputs the demodulated signal. is input to the off-center correction circuit 2 at the next stage, and is configured to correct the step difference in the DC level due to the deviation of the axial center of the rotary head and output it. The off-center correction circuit 2 uses the sawtooth wave generated by the correction wave generation circuit 3 to correct the DC step difference that occurs when switching heads.
A variable resistor VR is connected so that the slope of the sawtooth output waveform (including changes in the opposite direction) can be changed. This variable resistor VR is V shown by the broken line.
The resistance value can be adjusted by a knob provided on the outside of the TR device.

In such a configuration, for example, when a tape recorded on another VTR is being played back, the audio signal played back via the rtJ device width converter etc. is panned to the FMIaII device 1. As shown in Figure 4(b), the demodulated output has a different DC level before and after head switching due to off-center deviation, and if it is output directly to the line out terminal, it will contain buzz noise. becomes. Therefore, the correction wave generation circuit 3 generates a sawtooth wave synchronized with the head switching timing shown in FIG. 4(a), and the slope of the 9-sawtooth wave is created using the variable resistor 11VR as shown in FIG. 4(C). By adjusting the correction waveform to cancel the step difference in the DC level by changing the correction m of This results in a small output. Therefore, even if the off-center position of the VTR used for recording is different, it is possible to apply the optimum amount of off-center correction from outside the device to each recording tape during playback, and to hear good playback sound. .

FIG. 5 is a block diagram showing a second embodiment of the present invention.

In this embodiment, the external W! shown in FIG. 1. Instead of the VR, a variable resistor VR with a switch SW is used, a signal detection circuit 4 is connected to the switch SW, the audio signal output from the demodulator 1 is detected, and the mute circuit 5 is activated depending on the magnitude of the output signal.
The demodulated output is input to the mute circuit 5 via the off-center correction circuit 2, and output to the line-out terminal or the like.

In such a configuration, the signal detection circuit 4 is activated by turning on the switch SW, muting when an audio signal is output, and canceling the mute only when there is no signal or a small signal is output, thereby controlling the external connection during VR adjustment. Even when the gain of the amplifier is raised, no audio signal is output, and VR adjustment can be easily performed even when a non-signal part of the tape is being played back.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

This embodiment is applied to a device equipped with a noise reduction circuit, and the external adjustment means V shown in FIG.
Instead of R, use a variable resistor VR with switch SW,
A switch SI or a switch circuit that operates in conjunction with the operation of this switch SW is connected to the switch SW, and the demodulated output outputted through the off-center correction circuit 2 is sent to the switch S1.
a nozzle reduction circuit 6 and an output amplifier 7,
Alternatively, it is configured to lead directly to the output amplifier 7.

In such a configuration, if the noise reduction circuit 6 is a compression/expansion type noise reduction circuit, the buzz caused by the DC stage difference generated in the demodulator 1' will be converted to a low level, so the noise will be reduced. If VR adjustment is to be performed using the output that has passed through the reduction circuit 6, it will be necessary to further increase the sound quality of the externally connected amplifier or television receiver. Therefore, when adjusting the VR, it is better to use the switch sw attached to the variable resistor VR to input the output of the circuit 6, that is, the output of the off-center correction circuit 2, directly to the line out terminal or RF modulator via the output amplifier 7 to reduce the buzz noise. This means that the monitoring efficiency is good in reducing the amount of water. Therefore, in this circuit, when the VRII is adjusted, the switch $1 is operated at the same time as the switch sw is turned on, and the noise reduction circuit 6 is disconnected, so that the power of the circuit 6 can be directly monitored.

FIG. 7 is a block diagram showing a fourth embodiment of the present invention.

This embodiment is constructed so that it is possible to easily correct the step difference that occurs in the demodulated output level due to the amount of off-center when there is no audio signal recorded on the recording tape. A differentiating circuit 82, a display drive circuit 9, and a display 10 are installed in the circuit shown in FIG. The display drive circuit 9 is operated according to the magnitude of the correction, and the quality of the correction can be visually judged on a display 10 such as a light emitting diode or a level meter.

In such a configuration, the output of the off-center correction circuit 2 is differentiated by the differentiation circuit 8, and if the correction amount of the circuit 2 does not match, the differential output is as shown in FIG. 8(a) or (b). produces whisker-like pulses at the bottom or top. When the correction amounts completely match, the waveform after differentiation also becomes almost a straight line as shown in FIG. 8(C). Therefore, by inputting such a pulse to the display drive circuit 9 to drive the light emitting diode and level meter, it is possible to visually adjust the correction amount to VH2. Further, by extracting the differential waveform only when switching heads, it is possible to configure the correction amount to be adjusted to VR even when an audio signal is input.

[Effects of the Invention] As described above, according to the present invention, in a magnetic recording and reproducing apparatus that uses a rotary head to record and reproduce audio signals on a tape by FM modulation, an external adjustment means is provided in the reproduction circuit system. , a correction wave signal generating means and a correction means are provided to correct the step difference in the DC level of the FM demodulation output that occurs when switching heads, so a tape recorded with any other VTR device can be corrected with a simple correction circuit configuration. It is possible to provide an optimal amount of off-center correction for the object, and it also becomes possible for general users to easily adjust this from the outside.

Therefore, of course when playing self-recorded tapes,
Even when playing back tapes recorded on other machines or after head replacement, the buzzing noise that occurs when switching heads can be reduced or eliminated, and extremely high-quality audio output can be obtained. Therefore, recording tapes and VTR devices can be made compatible.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram illustrating the off-center of the center axis of the rotating cylinder of a VTR device, Fig. 2 is an explanatory diagram illustrating the DC level step difference of the demodulated output caused by the amount of off-center, and Fig. 3 is an explanatory diagram illustrating the difference in DC level level of the demodulated output caused by the amount of off-center. A block diagram showing a first embodiment of an audio tracking correction circuit of a magnetic recording and reproducing device, FIG. 4 is an explanatory diagram of the operation of the circuit shown in FIG. 3, and FIG. 5 is a block diagram showing a second embodiment of the present invention. FIG. 6 is a block diagram showing a third embodiment of the invention, FIG. 7 is a block diagram showing a fourth embodiment of the invention, and FIG. 8 is an explanatory diagram of the operation of the circuit shown in FIG. 1...4 IWA device 2...Off center correction circuit 3.
...Correction wave generation circuit vth point...Variable resistor agent Patent attorney Kensuke Norichika (one idiot) Figure 1 Figure 3 Whistle 2 Figure iF Figure 4 Figure 5 Figure 7, Figure Whistle 6 Figure 8 (0) -Y--r- 3,)-on-top- (C) □

Claims (1)

[Claims] A demodulating means for demodulating audio signals alternately reproduced from a magnetic tape recorded with frequency modulation using a plurality of rotating heads, a correcting means for correcting a step in the DC level of the demodulated output that occurs when switching heads, and a correcting means for correcting the level difference in the DC level of the demodulated output that occurs when switching the heads, and the timing of switching the heads. A correction wave signal generation means for creating a synchronized correction wave signal and supplying it to the correction means is connected to the correction wave signal generation means, and a correction amount is generated from outside the device. 1. An audio tracking correction circuit for a magnetic recording/reproducing device, characterized in that the circuit includes an external adjustment means capable of adjusting the sound.