JPS59142709A - Eliminating device of switching noise - Google Patents

Abstract

PURPOSE:To obtain a playback sound signal which is highly faithful to an original sound having no switching noise by a helical scanning system by equalizing signal voltage differences at connection parts of signals originating from the offset voltage difference and sensitivity difference between demodulation circuits. CONSTITUTION:The output of a low-pass filter 41 and the output of an adding circuit 10 are inputted to a differential amplifier 16. The output of the differential amplifier 16 is inputted while the 4th switching circuit 17 is closed, and this inputted difference signal controls the sensitivity of an FM demodulator 32 through an RC filter circuit 18 which supplies a proper control time constant and a necessary buffer amplifier 22. A control system for sensitivity difference fetches information on the difference between demodulation outputs of both demodulation circuits when both rotary heads 11 and 12 are both active by the closure of a switching circuit 17 in response to the rise of a control signal S9 from L to H. This difference information shows the sensitivity difference between both demodulation circuits after offset voltage correction, and the sensitivity of a demodulator 32 is corrected on the basis of the difference information so that the sensitivity difference is eliminated, allowing both demodulation circuits to have coincident sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching noise removing device suitable for use in a reproducing system of a rotary head type magnetic recording/reproducing device.

For example, in a two-head helical scan magnetic recording/reproducing device, when an audio FM signal is recorded and played back by two rotary heads that form an overlap period in the active period, each of the two rotary heads records an overlap period of the signal. The demodulated signal of the reproduced FM signal which is reproduced in time series is spliced together to form a continuous signal.

However, in this case, an FM
If there is an offset voltage difference or a sensitivity difference between the demodulation circuits, the signal curves at this joint point will not match, resulting in switching noise.

The present invention provides a switching noise removal device for removing such switching noise, and will be described below with reference to one embodiment thereof.

FIG. 1 is a block diagram of the reproducing system of a two-head helical scan magnetic recording and reproducing apparatus to which the present invention is applied. 1 and 2 show the first and second rotating heads. In order to form an overlapping period between the active periods of the rotating heads 11 and 12: the audio 1"M signal recorded on a discontinuous inclined trunk on a magnetic tape 2 wrapped around a rotating cylinder with a wrapping angle of more than 1801f is rotated. The rotating heads 1 and 12 are reproduced alternately and in chronological order by the heads 11 and 12.
Each reproduced FM signal from the , and 52, respectively.

Note that an adder circuit 10, which will be described later, is provided between the low-pass filter 4□ and the fixed contact 5□. This switching circuit 5 is switched and controlled by a switching signal So input from an input terminal T1. Switching signal S. is the rotating head 1. The level state changes at a predetermined time within the overramp period of the active period of and 1□゛, and the movable contact 5. of the switching circuit 5 changes in the rHJ state. to the fixed contact 51, and rLJ
In this state, the movable contact 53 is switched and connected to the fixed contact 5□. As a result, the rotating head 11.1□ゝ and the demodulator 38.
The reproduced signals respectively reproduced and demodulated in time series from 32 are spliced into a negative continuous signal and sent to the output terminal T2.
taken out from

Further, the output of the low-pass filter 41 and the output of the adder circuit 10 are connected to the second and third switching circuits 60, respectively.
．． 62 to the first and second sample-and-hold circuits 70.7□. The sample-and-hold circuits 71 and 72 are arranged so that the rotating heads 11.1□ are
Each F when not in contact with air tape 2 (inactive period)
The offset voltage detected and held by both sample-and-bold circuits 71.7□ is used to detect the difference between the offset voltages detected and held by both sample-and-bold circuits 71. is added to an adder circuit 10 via an RC filter circuit 9 for providing .

Switching signal S. are the second and third switching circuits 61.
62, the signal is input to the first switch control circuit 111 via the inverter 12, and is directly input to the second switch control circuit 11□, respectively. In the switch control circuits 111 and 112, 131.13□ is a delay circuit;
141.14□ is a mono-multi pie break, and the output signal S of each delay circuit and each mono-multi pie break is
S, and each control signal S6 and S3 from Annex 1-K-1-15 and 152 to which S6 and S2 are input, respectively.
controls the second and third switching circuits 6 and 62.

Here, the second and third switching circuits 6. and 6□ are closed when control signals S6 and S3 are "H", and rL
Open when j.

Finally, the output of the low-pass filter 4□ and the addition time 10
The outputs of are respectively input to the differential amplifier 16.

The output of the differential amplifier 16 is taken in when the fourth switching circuit 17 is turned on, and this taken-in difference signal is subjected to FMM adjustment via an FLC filter circuit 18 that provides an appropriate control time constant and a necessary buffer amplifier 22. The sensitivity of the device 32 is controlled.

Switching signal S. is also input to the third switch control circuit 113 to control the fourth switching circuit 17. In the switching circuit 113, a switching signal S is generated.

are input to mono-multi pie breaks 19□ and 192, respectively. The output signal S7 of the mono-multi high flake 19 is directly input to one input terminal of the AND gate 20, and the output signal S8 of the mono-multi pie break 19□ is input to the other input terminal via the inverter 21. be done. The control signal S9 output from the ant gate 20 causes the fourth switching circuit 17 to operate.

Here, the fourth switching circuit 17 receives the control signal S.

It is formed when the voltage is rHJ, and it is opened when the voltage is "L".

The operation will be explained below with reference to the time chart in FIG. 2. In FIG. 2, A and B are demodulated waveforms corresponding to each head 1□ and 12, D is an overramp period, and t, ~t4 indicates the signal splicing time, and
Particularly, for the later harmonic waveforms A and B, the signal levels do not match during the overlap period.

First, to explain the offset voltage difference correction control system, the first sample-and-halt circuit 7I responds to the fall of the control signal S6 from "14" to rLJ immediately before the active period of the rotating head 11 starts. maintain the offset voltage of the demodulation system of the rotating head 1° during the inactive period of
This voltage is input to one input terminal of the differential amplifier 8, and the second sample ant-hold circuit 7□ activates the rotary head 12 in response to the fall of the control signal S from "I" to rLJ. holding the offset voltage of the demodulation system of the rotary head 12 during the inactive period immediately before the start of the period;
The voltage is input to the other input terminal of the differential amplifier 8.

The differential amplifier 8 outputs a difference signal responsive to the level difference between the two offset voltages. This difference signal is added by the adder IO to the output of the demodulation circuit corresponding to the rotating head 1□ so that the level difference between both offset voltages becomes 0.

This corrects the level difference between the demodulated outputs based on the offset voltage difference between the demodulated circuits.

Next, the control system for sensitivity difference will be explained.Control signal S.

Closing of the switching circuit 17 in response to the rise of rLJ to rHJ captures the difference information between the demodulated outputs from both demodulation circuits when both rotary heads 11.12 are in the active state.

This difference information represents the sensitivity difference between the two demodulation circuits after the above-mentioned offset voltage difference correction. Therefore, based on this difference information, the demodulator 3□
The sensitivities of are corrected, and the sensitivities of both harmonic circuits are matched. Note that this control can be carried out by changing the amplitude of the pulse if the FM demodulator is, for example, a pulse Callan 1-type.

Furthermore, by providing an appropriate difference in response time constant between the offset voltage difference control system and the sensitivity difference control system, reliable operation can be achieved.

The present invention is not limited to the above-described embodiments, but includes, for example, the switch control circuits 111 to 11. It is also possible to replace the switching circuit 17 with another pulse circuit.
It is also possible to provide the adder circuit at the front stage of the differential amplifier 16, and various other configurations can be taken, such as arranging the adding circuit on the rotary head II side or correcting the sensitivity of the demodulator 31.

As described above, according to the present invention, in the so-called helical scan method in which a continuous reproduction signal is formed by sequentially splicing each reproduction signal reproduced in time series from discontinuous tracks, the difference in offset voltage and sensitivity between demodulation circuits Since the signal voltage difference in the spliced portion of the signals is controlled to be equal, it is possible to obtain a reproduced audio signal with high fidelity to the original sound without switching noise.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram of a reproducing circuit according to an embodiment of the present invention, and FIG. 2 shows a waveform diagram for explaining the circuit. 1-12...Rotating head, 30.3□...FM demodulator, 41.42 -Low pass filter, 5.60.6□
, 17... Switching circuit, 71.72... Sample and hold circuit, 8.16... Differential amplifier,
1o...Adder, IL, 112.113...Switch control circuit procedural amendment (method) May 76, 1980 Director General of the Patent Office 1. Indication of the case 1988 Patent Application No. 15028 2 Invention Name switching noise removal device 3 Relationship with the case of the person making the amendment Patent applicant address 1-153 Suzuki-cho, Kodaira-shi, Tokyo 187
(0423) 42-1111 April 6, 1982 5, column of title of invention of application subject to amendment and column of title of invention of specification. 6. Contents of amendment (1) The entry in the column of the name of the temple of origin in the application form will be amended as shown in the attached sheet. (2) The description "Switching noise removal device (2)" in the column of the title of the invention in the specification is corrected to "Switching noise removal device." 7. List of attached documents

Claims (1)

[Claims] The first and second active periods form an overlapping period.
A rotary head type magnetic recording and reproducing device that records and reproduces FM signals using a rotary head, first and second FM demodulation circuits that demodulate each reproduced FM signal from the first and second rotary heads, respectively; first and second detection and holding circuits that respectively detect and hold each output level of the first and second FM demodulation circuits during each inactive period of the first and second rotating heads; the first and second FM during the overlap period when both rotating heads are in the active period;
a detection circuit that detects a level difference between both demodulated outputs of the demodulation circuit, and detects the first and second outputs by a difference signal responsive to the level difference between the respective output levels detected and held by the first and second detection and holding circuits, respectively. A second FM demodulation circuit corrects and controls a level difference between demodulated outputs based on an offset voltage difference between the first and second FM demodulation circuits, and a difference signal responsive to a level difference between the demodulated outputs detected by the detection circuit. A switching noise removal device that corrects and controls sensitivity differences between FM demodulation circuits.