JPH0447559A - magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the sound quality by outputting a hold signal to a prehold circuit during the time when an output voltage of a deviation amt. detecting means for outputting a voltage corresponding to a lapse of time after generating a reset pulse synchronized with a carrier wave is beyond a reference value. CONSTITUTION:The reset pulse synchronized with the carrier wave of an FM- modulated wave is generated one after another by reset pulse generating means (a leading edge detecting circuit and a trailing edge detecting circuit) 11 and 12, while a voltage corresponding to generating intervals of each reset pulse is generated successively by the deviation amt. detecting means 14. Then, when an output voltage exceeds a reference value corresponding to a max. allowable frequency deviation, the hold signal is generated by a hold signal output means 17, and a hold processing is carried out by the prehold circuit 4 for a generating period only. As a result, the hold processing and its time are performed in accordance with an actual lacking state of the carrier wave and a lacking period, etc., and an unnecessary hold processing and a hold processing over an excessive period of time are suppressed to the utmost. By this method, the sound quality in a hi-fi video, etc., is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording/reproducing device having a function of reproducing signals recorded by FM modulation.

[Conventional technology]

2. Description of the Related Art Hi-Fi video tape recorders (hereinafter referred to as Hi-Fi video) have been put into practical use for the purpose of improving sound quality in video tape recorders, which perform FM modulation on audio signals and record them.

The process of processing reproduction signals in such Hi-Fi video will be explained with reference to FIGS. 3 and 4, which are explanatory diagrams of the present invention. As shown in FIGS. 3(a) and 3(b), FM waves recorded on the magnetic tape are read alternately by two rotating audio heads for the A channel and the B channel. Then, by switching the input of the reading signal from each head using the head switching signal shown in FIG.
A nearly continuous synthesized FM wave as shown in the figure is obtained.

By demodulating this composite FM wave, as shown in Fig. 4(a),
An audio demodulated signal as shown in FIG. 1 is obtained, but if discontinuity or dropout of the FM carrier wave occurs when switching the heads, head switching noise as shown in A in the figure is generated. In order to reduce this noise, conventionally, as shown in FIG. A pre-hold circuit 26 consisting of a hold switch 24 and a hold capacitor 25 is provided between the amplifier 23 that amplifies and outputs the audio demodulated signal.

The control terminal 24a of the hold switch 24 is manually supplied with a pulsed hold signal that is synchronized with the switching timing of the head switching signal and set to a predetermined time width, for example, 1° μsec. When a signal is input, the hold switch 24 is turned off, and during this time, the terminal voltage of the hold capacitor 25, that is, the voltage level immediately before the hold signal is input, is held and input to the amplifier 23. Through such hold processing, an audio signal with the head switching noise removed is output as shown in FIG. 4(C).

[Problem to be solved by the invention]

However, since the above-mentioned hold processing is performed every time the heads are switched, the problem arises that the sound quality deteriorates. In other words, the FM when switching heads as described above
Discontinuities and omissions of carrier waves do not necessarily occur uniformly, and their duration varies in various ways, and sometimes they become continuous waves that do not cause head switching noise. However, in the above, halt processing is performed even in the case of continuous waves that can be reproduced faithfully by outputting them as they are without performing hold processing, and in the case of extremely short-term discontinuities or missing states, halt processing is performed. Since the hold process is uniformly performed over an excessively long period of time, the sound quality actually deteriorates.

[Means for Solving the Problems] In order to solve the above problems, the magnetic recording/reproducing device of the present invention obtains a demodulated signal from a composite FM wave obtained by sequentially switching read heads that read out FM modulated waves alternately. a demodulation circuit;
A pre-hold circuit is connected to the output end of the demodulation circuit and outputs the demodulated signal, and while the hold signal is input to the pre-hold circuit, the level of the demodulated signal immediately before input of the hold signal is A magnetic recording/reproducing device in which a signal substantially held at is output from the pre-hold circuit, wherein a reset pulse is generated in synchronization with at least one of a rise and a fall of a carrier wave of an FM modulated wave. a generating means, a deviation amount detecting means for outputting a voltage according to the elapsed time after the generation of the reset pulse;
The present invention is characterized in that a hold signal output means is provided for outputting the hold signal while the output voltage of the deviation amount detection means exceeds a reference value.

[For production]

According to the above configuration, the reset pulse generation means sequentially generates cent pulses in synchronization with the carrier wave of the FM modulated wave, and the deviation detection means sequentially generates a voltage corresponding to the generation interval of each reset pulse. generated. The peak value of this voltage corresponds to the amount of instantaneous frequency deviation from the reference carrier frequency (carrier frequency when no modulation is performed). Therefore, if a carrier wave discontinuity or dropout condition occurs in the composite FM wave when switching the read head, the frequency in this region will deviate from the maximum allowable frequency deviation during FM modulation. Therefore, if the output voltage from the deviation amount detection means exceeds the reference value corresponding to the maximum allowable frequency deviation, discontinuity or missing state may occur in the carrier wave of the synthesized FM wave during this time. It can be assumed that there is

In this way, a hold signal is generated based on the actual carrier wave missing state, etc., and the above-mentioned hold processing is performed in the pre-hold circuit only during the generation period of this hold signal. As a result, hold processing and its time are performed according to the actual carrier wave missing state and missing period, and unnecessary hold processing or hold processing that lasts an excessively long time can be suppressed as much as possible. The sound quality can be improved more than before.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

The magnetic recording/reproducing apparatus of this embodiment configured as a Hi-Fi video is provided with an audio signal demodulation circuit as shown in FIG. 1 in order to demodulate an audio signal from the synthesized FM wave.

This circuit includes a limiter 1 that limits the amplitude of the synthesized FM wave input to it and shapes it into a rectangular wave whose rising and falling edges are almost perpendicular, and a limiter 1 that demodulates the audio signal from the output of this limiter 1. A demodulator (demodulation circuit) 2 and an amplifier 3 that amplifies and outputs the output from the FM demodulator 2.
, a pre-hold circuit 4 interposed between the FM demodulator 2 and the amplifier 3, and a hold signal generating section 5 that outputs a hold signal to be described later to the pre-hold circuit 4.

The pre-hold circuit 4 has a hold switch 6 which turns the input of the signal output from the FM demodulator 2 to the amplifier 3 into a FF state, and has one end connected to the input line to the amplifier 3 and the other end. and a hold capacitor 7 which is grounded. The hold switch 6 is designed to cut off the input from the FM demodulator 2 to the amplifier 3 while the hold signal generated by the hold signal generator 5 is input to the control terminal 6a provided thereon. It is designed to be turned OFF.

The hold signal generating section 5 that generates the above-mentioned hold signal includes a rise detection circuit 11, a fall detection circuit 12, and an integration circuit consisting of a resistor 13, a capacitor, and a capacitor 14, which are connected in series between the voltage Vcc and the ground. We are prepared. The rising edge detection circuit 11 and the falling edge detection circuit 12 each consist of a monostable multi-high break, and receive a rectangular wave shaped by the limiter 1, respectively. The rising edge detection circuit 11 uses the rising edge of the rectangular wave input thereto as a trigger input, while the falling edge detection circuit 12 uses the falling edge of the rectangular wave inputted therein as a trigger input, and outputs a pulse. It has become.

Each output pulse of the rise detection circuit 11 and fall detection circuit 12 is inputted to the control terminal 16a of the integral reset switch 16 through the OR circuit 15. This integral reset switch 16 is a connection point between the resistor 13 and the capacitor 14 of the integral circuit (hereinafter referred to as the charging voltage output point 1p).
and ground, and is turned on to ground the charging voltage output point ip every time a pulse signal is input to the control terminal 16a. At this time, the capacitor 14 is discharged and the terminal voltage of the capacitor 14 becomes zero potential, thereby causing the integration circuit to rise.

A hold signal output circuit (hold signal output means) 17 is further connected to the charging voltage output point ip. This hold signal output circuit 17 consists of a monostable multivibrator with variable pulse width, and when the input voltage to this hold signal output circuit 17, that is, the voltage at the charging voltage output point rp exceeds the threshold voltage vth. A pulse-like signal is output from the moment the state continues (until the maximum setting time elapses if the duration exceeds the maximum setting time, for example, 10 μsec).

This pulsed signal is input as a hold signal to the control terminal 6a of the hold switch 6.

The operating state of the magnetic recording/reproducing apparatus equipped with the audio signal demodulation circuit configured as described above will be described next.

Although not shown, the magnetic recording and reproducing device is provided with two rotating audio heads (hereinafter referred to as A channel head and B channel head) at positions 180 degrees opposite each other on the outer periphery of the rotating drum. A signal synthesis processing section for synthesizing the signals read by the A channel head and the B channel head is provided before the limiter 1. Above A channel head and B
As shown in FIGS. 3(a) and 3(b), the channel head alternately reads audio FM signals recorded on the magnetic tape. On the other hand, (C) in the same figure shows a head switching signal for selectively selecting the read signal of each head. Switching is performed at the timing when reading is performed, and as a result, a nearly continuous composite FM wave is generated in the signal synthesis processing section as shown in FIG. 2(d).

The synthesized FM wave generated in this way is input to the limiter 1, and further demodulated by the FM demodulator 2, as shown in FIG.
An audio demodulated signal as shown in a) is obtained. This audio demodulated signal will contain noise as shown by A in the figure if discontinuity or omission of the FM carrier wave occurs during the above-mentioned head switching. In the above configuration, in order to more appropriately perform noise reduction processing corresponding to the discontinuity or missing state of the FM carrier wave, the output from the limiter 1 is further transmitted to the rising edge detection circuit 11 and the falling edge detection circuit 12. It is now entered as .

Fig. 2 shows an example of an FM carrier wave input to the limiter 1. When such an FM carrier wave is input, the limiter 1 outputs a rectangular shape as shown in Fig. 2(b). A shaped wave is output. By inputting this shaped wave to the rising edge detection circuit 11 and the falling edge detection circuit 12, the OR circuit 15 outputs a signal according to each rising edge and falling edge of the shaped wave, as shown in FIG. This pulse train signal causes the integration reset switch 16 to be switched ON10FF one after another.

On the other hand, the capacitor 14 is charged from the voltage Vcc through the resistor 13, and the terminal voltage of the capacitor 14 is an integral that increases with a time constant according to the product of the capacitance of the capacitor 14 and the resistance value of the resistor 13. A wave appears. The capacitor 14 is grounded and reset through the integral reset switch 16 every time a pulse is input from the OR circuit 15 to the integral reset switch 16. As a result, as shown in FIG. 2(d), if each instantaneous frequency of the FM carrier wave is within the maximum allowable frequency deviation, the peak of each integral wave will reach the threshold of the hold signal output circuit 17. The hold signal is not output from the hold signal output circuit 17 because it is reset before the voltage vth is reached. That is, the above threshold voltage vth
A voltage value is selected that is slightly larger than the voltage corresponding to the maximum permissible frequency deviation in the FM modulated wave.

However, for example, as shown in FIG. 2(a), if a carrier wave missing period Td occurs corresponding to the head switching, the integral wave during this period will be as shown in FIG. 2(d). , exceeds the above threshold voltage vth, and from the time when this threshold voltage vth is exceeded until the normal FM carrier wave is input after head switching and the integral wave is reset, as shown in FIG. A pulse-like hold signal as shown in e) is output from the hold signal output circuit 17.

In this way, a hold signal with a time width τ corresponding to the discontinuity or missing period of the FM carrier wave is generated, and this is input to the control terminal 6a of the hold switch 6. While this hold signal is input, the hold switch 6 is turned off. As a result, a hold process is performed in which the input voltage to the amplifier 3 during this period is held at the terminal voltage of the hold capacitor 7, that is, the audio demodulated signal voltage immediately before the hold switch 6 is turned off. As a result, the noise in the area A in FIG. 4(a) is cut, and the audio output signal shown in FIG. 4(C) is obtained, which is output through the amplifier 3.

As described above, in the above embodiment, the hold signal to the pre-hold circuit 4 for reducing the head switching noise that occurs when switching heads is based on the discontinuity that actually occurs in the FM carrier wave when switching heads. The audio signal is generated with a time width τ corresponding to the missing period, and the hold processing of the audio signal is performed only during this time width τ. Therefore, if no discontinuity or omission occurs, the above-mentioned hold process is not performed, and if the degree of discontinuity or omission is small, a hold process is performed for a time corresponding to the degree. As a result, compared to the conventional apparatus, which performs hold processing by providing a uniform hold time of about 10 μsec each time the head is switched, the hold time can be suppressed to the minimum necessary, and unnecessary hold processing can be minimized.

As a result, the reproduced sound quality is improved.

In the above embodiment, the rise detection circuit 11 and the fall detection circuit 1 are used as reset pulse generation means for outputting a reset pulse in synchronization with the carrier wave of the FM modulated wave.
Although circuits are provided which synchronize with the rise and rise of the carrier wave with respect to 2, respectively, it is also possible to provide only one of the circuits. Further, in the above, the deviation detecting means for outputting a voltage corresponding to the instantaneous frequency deviation is constituted by the capacitor 14 which is charged from the voltage Vcc via the resistor 13. Any other circuit configuration may be used as long as it causes a predetermined change in the output voltage with the passage of time from the input of the pulse.

〔Effect of the invention〕

As described above, the magnetic recording and reproducing apparatus of the present invention includes a reset pulse generating means that generates a reset pulse in synchronization with at least one of the rise and fall of a carrier wave of an FM modulated wave, and A deviation detection means outputs a voltage according to elapsed time, and a hold signal output means outputs a hold signal to the pre-hold circuit while the output voltage of the deviation detection means exceeds a reference value. This is the configuration provided.

As a result, the hold processing in the pre-hold circuit and its time are carried out appropriately according to the state of missing carrier waves of the actual synthesized FM wave, the missing period, etc., and unnecessary hold processing or hold processing that lasts an excessively long time is avoided as much as possible. Therefore, it is possible to improve the sound quality in Hi-Fi video, for example, compared to the conventional one.

[Brief explanation of the drawing]

1 to 4 show one embodiment of the present invention. FIG. 1 is a block diagram showing the configuration of an audio signal demodulation circuit. FIGS. 2(a) to 2(e) are time charts showing the operation of each part in the hold signal generation process in the audio signal demodulation circuit. FIGS. 3(a) to 3(d) are time charts showing the operation of the processing circuit at the preceding stage of the audio signal demodulation circuit, respectively. FIGS. 4A to 4C are time charts showing the operation of each part during the process of processing an audio signal demodulated by the audio signal demodulation circuit. FIG. 5 shows a conventional example, and is a block diagram showing the configuration of an audio signal demodulation circuit. 2 is an FM demodulator (demodulation circuit), 4 is a front bold circuit,
11 is a rising edge detection circuit (reset pulse generation means), 1
2 is a falling detection circuit (reset pulse generating means), 14
1 is a capacitor (deviation detection means), and 17 is a hold signal output circuit (hold signal output means). Patent applicant: Sharp Co., Ltd.

Claims (1)

[Claims] 1. A demodulation circuit that obtains a demodulated signal from a composite FM wave obtained by sequentially switching read heads that alternately read out FM modulated waves;
A pre-hold circuit is connected to the output end of the demodulation circuit and outputs the demodulated signal, and while the hold signal is input to the pre-hold circuit, the level of the demodulated signal immediately before input of the hold signal is In a magnetic recording/reproducing device in which a signal substantially held at is outputted from the pre-hold circuit, a reset pulse generating means generates a reset pulse in synchronization with at least one of a rise and a fall of a carrier wave of an FM modulated wave. and a deviation detection means for outputting a voltage according to the elapsed time after the generation of the reset pulse, and a hold signal for outputting the hold signal while the output voltage of the deviation detection means exceeds a reference value. 1. A magnetic recording and reproducing device, characterized in that it is provided with an output means.