JPH02134768A - Switching noise reduction circuit - Google Patents

Abstract

PURPOSE:To prevent deterioration in the distortion factor caused by the changeover of rotary heads by detecting a required timing at a reproduction signal duplicated period by two sets of the rotary heads, outputting a switching signal and starting the primary interpolation. CONSTITUTION:An output of a head H3 detecting the turning position of rotary heads H1, H2 is applied to the title circuit, from which a duplicate period signal representing the period when reproducing signals by the heads H1, H2 are overlapped is outputted via a head changeover pulse generating circuit 21 of an overlapped period generating circuit 20, delay circuits 22, 23 and an exclusive OR circuit 25. A switching signal is outputted from an AND circuit 26 to which the overlapped period signal and a timing signal produced when a reproducing signal crosses the vicinity of 0 level via a mixing circuit 11 of a timing detection circuit 8, a comparator 13, a differentiating circuit 14 and a limiter circuit 17 are supplied and the reproduced output from the heads H1, H2 is switched via a head changeover switch 2. Then the primary interpolation to the reproduced output is started by a changeover noise elimination circuit 5L or 5R, a nearly consecutive reproduction signal is outputted to prevent the deterioration in the distortion factor of the reproduced output by the head changeover.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a reproduction circuit that reproduces an audio signal based on a signal obtained by switching detection signals from two rotary heads. The present invention relates to a switching noise reduction circuit that reduces switching noise generated when rotating heads are switched.

(Prior art) In a video tape recorder, an audio signal is used to
A method is used that enables high-quality recording by recording an M-modulated carrier wave, but since this recording and playback requires two rotating heads, problems occur when switching between them. It is necessary to eliminate switching noise.

FIG. 3 shows a conventional example of a circuit used to remove the switching noise described above, in which a demodulated audio signal is guided to a delay circuit 32 and a correction circuit 33 via a low-pass filter 31. . The output 33a of the correction circuit 33 is
The signal is led to a hold capacitor C connected to a hold circuit 35 via a resistor R, and the output 32a of the delay circuit 32 is connected to the hold circuit 35. Further, the bold circuit 35 is connected to the output of the delay circuit 34 to which a hold pulse indicating the hold timing is guided.

FIG. 4 is an explanatory diagram showing signal waveforms of main parts of the conventional example.

The delay circuit 32 delays the input signal by a time equal to the period t31, so at time T35,
When the last signal Sll from one rotary head is sent out, the first signal SI□ from the other rotary head appears at the output 33a of the correction circuit 33.

In other words, the hold circuit 35 is simultaneously given the level V31 of the last signal from one rotary head and the level ■3□ of the first signal from the other rotary head at time T3S. Therefore, the hold circuit 35 generates a voltage ■ that changes linearly to connect these two levels V, ..., V3□ in the period ta11 based on the output of the delay circuit 34. is generated, so the output 35a is:
A signal waveform that changes almost continuously appears, and noise accompanying switching of the rotary head is reduced.

(Problem to be Solved by the Invention) In the operation shown above, the relationship between the waveform of the audio signal and the timing of switching is as shown in FIG. 5, for example.
During the switching period, the level of the audio signal is
In the case where the maximum or minimum level is passed, the level V3'T at time T:17 and the level V3B at time T,8 are linearly interpolated, and as a result, the period L3
The signal waveform S appearing at the output of the hold circuit 35 at □
, 3' are greatly separated from the source waveform S11,
This resulted in deterioration of the distortion rate.

The present invention was devised to solve the above-mentioned problems, and an object of the present invention is to provide a switching noise reduction circuit that can prevent deterioration of distortion caused by switching of rotating heads.

(Means for Solving the Problems) The switching noise reduction circuit of the present invention reproduces an audio signal based on a signal obtained by switching detection signals from two rotating heads, and also reproduces the reproduced audio signal. A head changeover switch that is applied to a switching noise reduction circuit that reduces switching noise generated when switching the rotary heads by performing linear interpolation, and that switches the detection signals sent out from the two rotary heads; a switching noise removal circuit that performs linear interpolation;
an overlapping period signal generation circuit that sends out an overlapping period signal indicating an overlapping period of the detection signals sent out from the two rotary heads; and a timing detection section that detects the timing at which the level of the reproduced audio signal crosses near the 0 level. , when the output of the timing detection section indicates a cross-section of the level of the audio signal near the 0 level, and the overlapping period signal indicates that the detection signals overlap, a switching signal is generated to send a switching signal indicating switching timing to the head switching switch; The switching noise removal circuit starts linear interpolation according to the switching signal.

(Function) By using the timing detection section, the timing at which the audio signal level crosses near the O level is detected, and the switching signal generation circuit detects the timing at which the output of the timing detection section crosses the audio signal level near the 0 level. shows,
And when the overlapping period signal indicates that the detection signals overlap, a switching signal indicating switching timing is generated. By sending this switching signal to the head switching switch and switching noise removal circuit, switching of the rotational end and linear interpolation are performed in synchronization with the timing at which the audio signal crosses a level near the 0 level.

(Embodiment) FIG. 1 is a block diagram showing the electrical configuration of an embodiment of the present invention.

In the figure, detection signals H, . . . from two rotary heads H, .
.
Connected to 3R.

The outputs of the bandpass filters 3L and 3R are respectively guided to FM demodulation circuits 4L and 4R, and
The outputs of M demodulation circuits 4L and 4R are switched to noise removal circuit 5L.
, 5R.

The outputs of the switching noise removal circuits 5L and 5R are connected to noise reduction circuits 6L and 6R, and the outputs of the noise reduction circuits 6L and 6R are connected to the audio signal SL through amplifiers 7L and 7R.

The signal is sent as SR to the mixing circuit 11, which is a component of the timing detection section 8, and to the outside.

The output of the mixing circuit 11 is guided to a bypass filter 12 whose cutoff frequency is set to 5 KHz, and a comparator 13, and the output of the comparator 13 is guided to a differentiating circuit 14.
Then, the output of the differentiating circuit 14 is sent to the rectifier circuit 15,
The output of 5 is sent to the limiter circuit 17 via the amplifier 16.
Each is connected. Also, the bypass filter 12
The output of the detector circuit 18 is led to a detection circuit 18, and the output of the detection circuit 18 is led to a comparator 19.

The output of the magnetic head H3 that detects the rotational position of the rotating heads H, H2 is connected to a head switching pulse generation circuit 21 which is a component of the overlap period signal generation circuit 20, and the output of the head switching pulse generation circuit 21 is , three delay circuits 2
2, 23, and 24 as a trigger signal.

The outputs of the delay circuits 22 and 23 are led to an EXOR gate 25, and the overlapping period signal 25a, which is the output of this EXOR gate 25, is sent to the switching signal generation circuit 2 consisting of an AND gate.
is connected to one input of 6. Further, the output of a limiter circuit 17, which is a component of the timing detection section 8, is connected to the other input terminal of the switching signal generation circuit 26.

The switching signal 26a that is the output of the switching signal generation circuit 26 and the output 24a of the delay circuit 24 are led to two inputs of a changeover switch 27, and the output 27a of this changeover switch 27 is the output of the rotating head H,,H,. The head changeover switch 2 and the switching noise removal circuit 5L serve as signals indicating switching timing.

It has been sent to 5R. Further, the output of the comparator 19 is introduced into the switching switch 27 as a signal for controlling switching.

FIG. 2 is a timing chart showing the output waveforms of the main signals, and the operation will be explained below with reference to the same figure as necessary.

The carrier waves detected by the rotating heads H, , H2 are passed through the head changeover switch 2 to band pass filters 3L, 3.
Since the carrier wave is guided to R, the carrier wave is separated into left and right waves, and then guided to FM demodulation circuits 4L and 4R, where the audio signal is demodulated. And then, the switching noise removal circuit 5L.

5R removes noise associated with switching,
After the level is expanded by the noise reduction circuits 6L and 6R, the signal is sent to the outside as an audio signal.

In the following, the operation of generating pulses that determines the timing of the switching of the head changeover switch 2 and the primary interpolation operation of the switching noise removal circuits 5L and 5R will be explained.

The transmission of the detection signal H11 output from the rotary head H5 ends at time T2°, and the transmission of the detection signal H12 from the rotary head H2 begins at time T2□. And these two detection signals H, .

The period L1□ during which H and □ overlap with each other is approximately 400 μs.

On the other hand, the signal generated by the head switching pulse generation circuit 21 based on the output from the magnetic hand H, is a signal indicating the time that is the reference time for switching the rotary heads H,,H. The output 22a of the derived delay circuit 22 is at time T2 when the output from the rotary head H2 appears.
At time T, which allows for a little margin in 1, the level changes from the rL level to the rHJ level (H31).

Similarly, the level of the output 23a of the delay circuit 23 changes from the "L" level to the "H" level (H, 2 ). Therefore EX
The overlapping period signal 25a, which is the output of the OR gate 25, outputs an "H" level (H33) indicating that outputs are being sent together from the two rotating heads H1+H2 during the period tll from time T1 to time T2. .

Output 11a of the mixing circuit 11 (indicating a signal with a frequency of 5K11z) is guided to the output 13a of the comparator 13
When the level of output 11a becomes positive, "I]"
Level (H41-H, 4), rl when negative
, J level (H4, to L43) appears. Therefore, the output 13a of the differentiating circuit 14 changes from "H" level to "
A negative pulse appears when the level changes to "L" level, and a positive pulse appears when the level changes from the "L" level to the rl() level.

The pulse on the output 14a of the differentiating circuit 14 is given to the limiter circuit 17 via the rectifier circuit 15 and the amplifier 16.
A short pulse PHI~P27 appears every time a crosses the 0 level (time 'T''II~T, ,).

As a result, the switching signal 26a that is the output of the switching signal generation circuit 26 includes the overlapping period signal 25 within the period tll.
Pulse P2□ that appeared at a ~ Pulse P2□ equal to PZS
, ~P2SI will appear.

On the other hand, since the cutoff frequency of the bypass filter 12 is set to 5 KHz, the 5 KHz signal passes through the bypass filter 12 and is guided to the detection circuit 18. Therefore, the output of the detection circuit 18 becomes positive, and the output 19a of the comparator 19 becomes rH, level.

The changeover switch 27 is configured to send out the output of the switching signal generation circuit 26 when the output 19a of the comparator 19 reaches the r) (J level), and send out the output of the delay circuit 24 when the output 19a of the comparator 19 reaches the "L" level. Therefore, the pulses P2□1 to P2,1 appearing on the switching signal 26a are applied to the head changeover switch 2 and the switching noise removal circuits 5L and 5R.

Further, the head changeover switch 2 and the changeover noise removal circuits 5L and 5R are configured to start operating in synchronization with the first pulse guided within the period L1□ in which the rotary heads H, , H2 can be switched. Therefore, the audio signal SL,
The operation starts at time T, □ when a pulse P2□, indicating the timing when the level of S, crosses the 0 level, is introduced.

Therefore, H of the rotary head that detects the carrier wave.

The switching from H2 to H2 and the linear interpolation that reduces the noise associated with the switching are performed at time T1□.

On the other hand, the output 24a of the delay circuit 24 is transmitted to the two rotating heads H, .
Since the configuration is such that the level changes from the "L" level to the "H" level (H34) at time Tel, which is approximately in the middle of the period L1□ during which the outputs from H2 are outputted in an overlapping manner, the audio signal SL+SR There are very few signal components of 5KHz or higher, the output of the bypass filter 12 is at an extremely small level, and the output of the comparator 19 is "L".
level, the head changeover switch 2 and the switching noise removal circuits 5L and 5R output the output 2 of the delay circuit 24.
4a, at time T1. Initiate its action by smell.

The timing of linear interpolation affects the sound quality only when the audio signals SL, S, contain high frequency components, and when playing bass solo etc. When the audio signals SL and SR consist only of frequency components, the timing of linear interpolation does not affect the sound quality. Therefore, as explained above, in this embodiment, the frequency components of the audio signals SL and SR are only composed of low frequency components (5 kHz or less). Then, during a period of about 4001 Js during which the outputs from the two rotating heads H, , H2 overlap, 1. In □, when there is a possibility that the output 11a of the mixing circuit 11 does not cross the 0 level, there is a period, and at time T34, which is approximately in the center of □, the rotating heads H, , H, are switched and linear interpolation is performed. Therefore, it is possible to avoid the possibility that switching will not be performed.

Note that the present invention is not limited to the above embodiment, and the cutoff frequency of the bypass filter 12 can be set to a frequency such as 4 KHz, which always crosses the 0 level at least once within the period t1□. .

Further, regarding the timing detection section 8, the audio signals S, , S
Every time the level of R crosses the 0 level, pulse P2□1~P
Although the configuration in which signals 2 and 1 are sent out has been described, it is also possible to have a configuration in which a pulse is sent out only when the level of the audio signals S, SR crosses the O level, for example, when it changes from negative to positive. It is.

(Effects of the Invention) The switching noise reduction circuit according to the present invention uses an overlapping period signal generation circuit to detect an overlapping period of detection signals sent from two rotary hands, and also uses a timing detection section to detect an overlapping period of detection signals sent from two rotating hands. By detecting the timing at which the level of the input audio signal crosses near the 0 level, a switching signal indicating the switching timing is generated, and the rotary head is switched and linear interpolation is performed in accordance with this switching signal. Since linear interpolation is performed when the change in the level of the audio signal shows a change that approximates a linear change, it is possible to prevent the deterioration of the distortion rate that occurs when the rotating head is switched. It becomes possible.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the electrical configuration of an embodiment of the present invention, Fig. 2 is a timing chart showing the output waveforms of main signals, and Fig. 3 is an electrical diagram of a conventional switching noise removal circuit. FIGS. 4 and 5 are explanatory diagrams showing signal waveforms of the main parts of the conventional example shown in FIG. 3. 2...Head changeover switch 5L, 5R...Switching noise removal circuit 8...Timing detection section 20...Overlapping period signal generation circuit 26...Switching signal generation circuit H,, H□...Rotation Head Figure 2 ■ Figure 4 Society 11 Figure 5 3B

Claims (1)

[Scope of Claims] 1) The rotating head A switching noise reduction circuit that reduces switching noise generated due to switching, comprising: a head selection switch that switches detection signals sent from the two rotating heads; a switching noise removal circuit that performs the linear interpolation; an overlapping period signal generation circuit that sends out an overlapping period signal indicating an overlapping period of the detection signals sent out from the two rotary heads; and a timing detection section that detects the timing at which the level of the reproduced audio signal crosses near the 0 level. and, when the output of the timing detection section indicates a cross-section of the level of the audio signal near the 0 level, and the overlap period signal indicates an overlap of the detection signals, a switching device that sends a switching signal indicating switching timing to the head switching switch. A switching noise reduction circuit comprising: a signal generation circuit, wherein the switching noise removal circuit starts linear interpolation according to a switching signal.