JPH10302388A - Audio signal reproducing device for magnetic recording and reproducing device - Google Patents

Abstract

(57) [Summary] (With correction) [PROBLEMS] To appropriately determine a dropout and reproduce a sound signal without noise when there is a large level difference between FM modulation signals from two rotating magnetic heads. When there is a dropout, a dropout detection circuit detects a dropout period from an output signal, and a mute circuit sets a demodulated audio signal in a mute state during that period. However, this dropout detection circuit is not operated while the switching noise correction pulse for operating the switching noise correction circuit for correcting the level difference of the FM modulation signal is at a high level.
At the selected point of the magnetic head, the attenuated signal is further attenuated due to transient characteristics such as a band pass filter. At this time, by preventing muting in this way, the generation of auditory noise is prevented I do.

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, and more particularly to an audio signal reproducing apparatus.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration of an audio signal reproducing apparatus of a conventional magnetic recording / reproducing apparatus. FIG. 4 is a waveform chart illustrating the operation of FIG. Hereinafter, the configuration and operation will be described with reference to FIGS.

The two rotating magnetic heads 103 alternately reproduce the FM modulation signals recorded on the magnetic tape 101 (FIG. 4A). Note that the magnetic head 103 is also used when recording the FM modulation signal on the magnetic tape 101. The FM modulation signal reproduced by the magnetic head 103 is supplied to the head amplifier 105.

The head amplifier 105 has two channels in accordance with the two magnetic heads 103. Each channel has an amplifier and amplifies the FM modulation signal from each magnetic head 103. And each terminal 10 of the head amplifier 105
5a and 105b. The selector 105c of the head amplifier 105 alternately selects the FM modulation signal from each of the terminals 105a and 105b with the head switching pulse shown in FIG. 4B, and performs a series of reproduction FM modulation signals (PB F
M) (FIG. 4 (c)), and the reproduced FM audio processing device 107
To supply.

[0005] The band pass filter (BPF) 109 is
The voice FM band is extracted from the input FM modulation signal.

[0006] The level of the FM modulation signal for reproduction varies depending on the characteristics of the magnetic tape to be recorded. Therefore, the level of the FM modulation signal is detected by the AGC detection circuit 113. Then, the auto gain controller (AGC) 111
The level of the FM modulation signal from the bandpass filter 109 is made constant by the control signal from the GC detection circuit 113. This solves the problem of demodulation caused by the difference in the level of the reproduced FM modulation signal due to the difference in the magnetic tape.

The demodulation circuit 115 demodulates the FM modulated signal whose level is controlled to be constant by the auto gain controller 111, and converts it into a demodulated audio signal in an audible audio frequency band. This demodulated audio signal is supplied to a switching noise correction circuit (SW.NC) 121.

The switching noise correction circuit 121 detects noise and phase difference caused by discontinuity when the head amplifier 105 alternately selects two FM modulated signals reproduced from the two magnetic heads 103 (FIG. 4 (c)). This is a circuit for reducing the demodulation error noise generated in the demodulated audio signal by enlarging the selected point in ()).

The switching noise correction requires a timing of a period for compensating a noise width at the selected point, which is a basis of the demodulation error noise. Therefore, a switching noise correction (SWNC) pulse generating circuit 11 is provided.
9 generates a switching noise correction pulse (FIG. 4E) based on the head switching pulse (FIG. 4B), and generates a switching noise correction circuit (SW.N.
C. ) 121.

The switching noise correction circuit 121 is a demodulation circuit 115 based on the switching noise correction pulse.
Of the demodulated audio signal from the
To the terminal 123a. A terminal 123b of the mute circuit 123 is for putting the demodulated audio signal in a mute state, and is connected to a predetermined bias power supply.

The selector 123c of the mute circuit 123
A terminal 123a or 123b is output by a dropout detection pulse from a dropout detection circuit 117 described later.
Select one of During normal playback, the selector 12
3c selects the terminal 123a and makes it a demodulated audio output (FIG. 4
(F)).

When the switching noise correction circuit 121 is not provided and the switching noise correction is not performed, the demodulated voice output has a waveform including noise as shown in FIG.

Next, for example, there is a case where the magnetic tape 101 has a flaw for a moment and a short drop occurs in the reproduced FM modulation signal. This lack cannot be corrected by the auto gain controller 111 called dropout. The operation of the audio signal reproducing device of the magnetic recording and reproducing device in this case will be described with reference to the waveform diagram of FIG.

If there is a dropout, the reproduced FM modulation signal from the head amplifier 105 has the waveform shown in FIG. When this is demodulated by the demodulation circuit 115, the demodulated audio output has noise in the dropout portion as shown in FIG. 5B.

Therefore, the dropout detection circuit 117
Detects a dropout period from the FM signal output from the auto gain controller 111 and supplies a dropout detection pulse shown in FIG.

The selector 123c of the mute circuit 123
The terminal 123b is selected during a period when the dropout detection pulse from the dropout detection circuit 117 is at the high level, and the demodulated audio signal from the switching noise correction circuit 121 is muted. Further, the terminal 123a is selected while the dropout detection pulse is at a low level. As a result, the demodulated audio output of the mute circuit 123 is
The waveform shown in FIG.

[0017]

The FM modulation signal recorded on the magnetic tape 101 has a level difference between the respective channels. The operation of the audio signal reproducing device of the magnetic recording and reproducing device in this case will be described with reference to FIG.

FIG. 6A shows two rotating magnetic heads 10.
3 shows the waveform of the reproduced FM demodulated signal when the FM modulated signals recorded on the magnetic tape 101 are each reproduced alternately. As shown, A Channel and B Channel
nel has a level difference.

FIG. 6B shows a waveform when the head amplifier 105 alternately selects them and outputs a series of reproduced FM modulation signals (PB FM). At the selected point, a large noise and phase difference occur as shown in the enlarged view due to discontinuity of the reproduced FM modulation signal.

The reproduced FM modulated signal from the head amplifier 105 passes through a band-pass filter (BPF) 109, but the level is attenuated by noise and a phase difference at a selected point as shown by a waveform in FIG. . When the FM modulated signal from the band pass filter (BPF) 109 passes through the auto gain controller 111 next time, the transient response characteristic of the auto gain controller 111 causes
As shown by the waveform (d), the level at the selected point is further attenuated.

The dropout detection circuit 117 detects the FM signal output from the auto gain controller 111. At this time, since the level is greatly attenuated at the selected point, the high level dropout detection pulse is muted during that period. 123. While the high-level dropout detection pulse is being input, the selector 123c of the mute circuit 123 selects the terminal 123b, and the demodulated audio signal from the switching noise correction circuit 121 as shown in the waveform of FIG. Is a demodulated audio output in which the is muted.

Since the muting is performed for each of the selected points with a short period and a constant period, the muting is perceived as noise.

Therefore, the present invention provides two Chas reproduced from a magnetic tape by at least two rotating magnetic heads.
It is an object of the present invention to provide an audio signal reproducing apparatus of a magnetic recording and reproducing apparatus which does not generate aural noise even if there is a large level difference between nnel FM modulation signals.

[0024]

At least two rotating magnetic heads for alternately reproducing an FM modulated signal recorded on a magnetic tape, and amplifying at least two channels of the FM modulated signal reproduced by the rotating magnetic head. A head amplifier that alternately selects a series of FM modulation signals in accordance with a head switching pulse, a filter unit that extracts a voice FM band from the FM modulation signal from the head amplifier, and an FM modulation signal from the filter unit Gain control means for suppressing fluctuations in the level of the audio signal, demodulation means for demodulating the FM modulated signal from the auto gain control means and outputting a demodulated audio signal in an audible audio frequency band, and reproducing FM signals from the magnetic heads. FM modulation at a selected point when a modulation signal is alternately selected by the head amplifier A switching noise correction pulse generating means for generating a switching noise correction pulse from the head switching pulse in order to correct demodulation error noise caused by the discontinuity of the signal; A switching noise correction unit that corrects the demodulation error noise of the demodulated audio signal from the demodulation unit with a switching noise correction pulse; and a dropout period detected from an FM modulation signal output from the auto gain control unit. A dropout detecting means for outputting a detection pulse, and a mute for outputting a demodulated audio signal from the switching noise correction means when the drop detection pulse is not input, and for setting a mute state when the drop detection pulse is input. ; And a stage,
The operation of the dropout detecting means is stopped during a period of the switching noise correcting pulse from the switching noise correcting pulse generating means.

[0025]

FIG. 1 shows a configuration of an embodiment of an audio signal reproducing apparatus of a magnetic recording / reproducing apparatus according to the present invention. FIG.
FIG. 3 shows a waveform diagram for explaining the operation of FIG. Hereinafter, the configuration and operation will be described with reference to FIGS.

The two rotating magnetic heads 3 are mounted on the magnetic tape 1
2 are alternately reproduced (FIG. 2 (a)). The magnetic head 3 is also used when recording the FM modulation signal on the magnetic tape 1. Magnetic head 3
The FM-modulated signal reproduced by is supplied to the head amplifier 5. A Channel and B Channel played back
The nel FM modulation signal has a large level difference as shown in FIG.

The head amplifier 5 has two channels in accordance with the two magnetic heads 3. Each channel has an amplifier and amplifies the FM modulation signal from each magnetic head 3. Then, the voltage is supplied to each terminal 5a, 5b of the head amplifier 5. The selector 5c of the head amplifier 5 uses the same head switching pulse as shown in FIG.
5b to select a series of reproduced FM signals by alternately selecting FM modulation signals.
The modulated signal (PB FM) (FIG. 2 (b))
It is supplied to the audio processing device 7. Terminal 5a by selector 5c
At the selection point at the time of the selection of (5) and (5b), as shown in the enlarged view of FIG.

A band pass filter (BPF) 9 extracts a voice FM band from an input FM modulation signal. At this time, the level is attenuated due to noise and phase difference at the selected point as shown in the waveform diagram of FIG.

The level of the FM modulation signal for reproduction varies depending on the characteristics of the magnetic tape to be recorded. Therefore, the level of the FM modulation signal is detected by the AGC detection (Det) circuit 13. Then, an auto gain controller (AGC) 11
Makes the gain of the FM modulation signal from the bandpass filter 9 constant by the control signal from the AGC detection circuit 13,
An FM modulated signal having the waveform shown in FIG. This solves the problem of demodulation caused by the difference in the level of the reproduced FM modulation signal due to the difference in the magnetic tape.

However, due to the transient response characteristic of the auto gain controller 11, the level at the selected point is further attenuated as shown in the waveform diagram of FIG.

The demodulation circuit 15 demodulates the FM modulated signal whose gain has been controlled by the auto gain controller 11 and converts it into a demodulated audio signal in the audible audio frequency band. This demodulated audio signal is supplied to a switching noise correction circuit (SW.N.
C. ) 21.

The switching noise correction circuit 21 is connected to the selected point (the two magnetic heads 3 in the head amplifier 5).
The noise and phase difference (when the selected point is enlarged and displayed in FIG. 2B) generated by the two FM modulation signals reproduced in the step (a) are further attenuated by the bandpass filter 9 and the auto gain controller 11. This is a circuit for correcting the demodulation error noise generated in the demodulated audio signal by the above portion.

The switching noise correction requires a timing of a period for compensating a noise width at the selected point, which is a basis of the demodulation error noise. Therefore, a switching noise correction (SW.NC) pulse generating circuit 19 is provided.
Generates a switching noise correction pulse (FIG. 2E) based on the head switching pulse and supplies it to the switching noise correction circuit 21.

The switching noise correction circuit 21 corrects the demodulated audio signal from the demodulation circuit 115 based on the switching noise correction pulse, and supplies the signal to the terminal 23 a of the mute circuit 23. Terminal 23b of mute circuit 23
Is for muting the demodulated audio signal, and is connected to a predetermined bias power supply.

The selector 23c of the mute circuit 23 selects one of the terminals 23a and 23b according to a dropout detection pulse from a dropout detection circuit 31 described later. During normal reproduction, the selector 23c is connected to the terminal 2
3a is selected as a demodulated audio output (FIG. 2 (g)).

Next, for example, there is a case where the magnetic tape 1 has a flaw for a moment and a short drop occurs in the reproduced FM modulation signal.
This lack cannot be corrected by the automatic gain controller 11 called dropout.

If there is a drop-out, the reproduced FM modulated signal from the head amplifier 5 is demodulated by the demodulation circuit 15,
The demodulated audio output when the selector 23c of the mute circuit 23 selects the terminal 23a generates noise in a dropout portion.

Therefore, the dropout detection circuit 31
A dropout period is detected from the FM signal output from the auto gain controller 11 and a dropout detection pulse as shown in FIG.

The selector 23c of the mute circuit 23 selects the terminal 23b while the dropout detection pulse from the dropout detection circuit 31 is at the high level, and sets the demodulated audio signal from the switching noise correction circuit 21 to the mute state.

The switching noise correction pulse (FIG. 2 (f)) is input to the dropout detection circuit 31 from the switching noise correction (SW.NC) pulse generation circuit 19. The dropout detection circuit 31 stops operating while the switching noise correction pulse is at the high level, and its output remains at the low level as shown in the waveform diagram of FIG.

Thus, the selector 2 of the mute circuit 23
Reference numeral 3c denotes a state where the terminal 23a is still selected and the selected point from the switching noise correction circuit 21 (the two FMs reproduced by the two magnetic heads 3 in the head amplifier 5).
The demodulated audio signal corresponding to the modulation signal is selected not to be muted.

In the present invention, the number of rotating magnetic heads for reproducing the FM modulation signal from the magnetic tape is not limited to two, but may be two or more. In this case, the configuration of the head amplifier 5 and the configuration of the head switching pulse may be changed so that a series of reproduced FM modulation signals is output from the head amplifier.

[0043]

As described above, according to the present invention, even if there is a large level difference between the FM modulation signals of the two channels reproduced by the two rotating magnetic heads, no auditory noise is generated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an audio signal reproducing device of a magnetic recording / reproducing device of the present invention.

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a block diagram showing a configuration of an audio signal reproducing device of a conventional magnetic recording and reproducing device.

FIG. 4 is a waveform chart for explaining the operation of FIG. 3;

FIG. 5 is a waveform chart for explaining the operation of FIG. 3;

FIG. 6 is a waveform diagram for explaining a problem of the audio signal reproducing device of the conventional magnetic recording and reproducing device.

[Explanation of symbols]

1 ... magnetic tape, 3 ... rotary magnetic head, 5 ...
・ Head amplifier, 7 ・ ・ ・ Reproduced FM audio processor, 9 ・
..Band pass filter (BPF), 11 ... Auto gain controller, 13 ... AGC detection (Det)
Circuit, 15 ... demodulation circuit, 19 ... switching noise correction (SW.NC) pulse generation circuit, 21.
..Switching noise correction circuit (SW.NC),
23: Mute circuit, 31: Dropout detection circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 15/14 G11B 15/14 Y

Claims (2)

[Claims] At least two rotating magnetic heads for alternately reproducing an FM modulation signal recorded on a magnetic tape; amplifying at least two channels of an FM modulation signal reproduced by the rotating magnetic head; A head amplifier that alternately selects according to a pulse to generate a series of FM modulation signals, a filter unit that extracts a voice FM band from the FM modulation signals from the head amplifier, and a level variation of the FM modulation signal from the filter unit Auto-gain control means for suppressing noise, a demodulation means for demodulating an FM-modulated signal from the auto-gain control means and outputting a demodulated audio signal in an audible audio frequency band, and a reproduction FM-modulated signal from each of the magnetic heads. Discontinuity of FM modulation signal at selected point when selecting alternately by head amplifier A switching noise correction pulse generator for generating a switching noise correction pulse from the head switching pulse to correct demodulation error noise caused by the switching noise correction; and the switching noise correction pulse from the switching noise correction pulse generator. A switching noise correction unit that corrects the demodulation error noise of the demodulated audio signal from the demodulation unit, a dropout period is detected from the FM modulation signal output from the auto gain control unit, and a dropout detection pulse is output. A dropout detection unit, a mute for outputting a demodulated audio signal from the switching noise correction unit when the dropout detection pulse is not input, and for setting a mute state when the dropout detection pulse is input. ; And a stage, the period of the switching noise compensation pulse from the switching noise compensation pulse generating means, the audio signal reproducing apparatus of a magnetic recording and reproducing apparatus characterized by stopping the operation of the dropout detector. 2. An output terminal of said switching noise correcting pulse generating means, wherein an input terminal of said dropout detecting means is connected to an output terminal of said auto gain control means. Audio signal reproducing device of the magnetic recording and reproducing device.