JPS6252706A - Dropout compensating circuit - Google Patents

Abstract

PURPOSE:To prevent listening displeasure to ears by providing a control circuit permitting the replacement when the result of discrimination by a level detection circuit discriminating the quantity for a signal level of a high fidelity sound based on a prescribed level is larger and muting the high fidelity sound when smaller. CONSTITUTION:In a dropout compensating circuit 11, a control circuit 13 is operated depending on the quantity of the signal level of the high fidelity sound just before a dropout takes place through the detection of a level detection circuit 12 if a dropout takes place in the high fidelity sound so as to select either the replacement by the normal sound or the muting. Thus, even when the normal sound is recorded automatically at a prescribed signal level by an automatic level control circuit at recording, the normal sound is replaced into the high fidelity sound only at a large signal and the high fidelity sound is muted at a small signal. Thus, the inconvenience that a large sound is mixed suddenly at small sound volume reproduction and unnatural and displeasant listening is avoided in an excellent way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dropout compensation circuit that replaces the dropout portion of high-fidelity audio with normal audio.

[Prior Art] A video tape recorder that performs FM modulation on an audio signal, uses a frequency band intermediate between the FM modulated luminance signal and the low frequency conversion chromaticity signal, and multiplexes the recording onto a video track is a high-fidelity audio signal. In addition to the normal audio recorded on audio tracks along the side edges of the magnetic tape,
It is also possible to simultaneously record signals from different sound sources as high-fidelity audio. However, in general,
High-fidelity audio and normal audio often record the same audio, and differences in the sound quality of reproduced audio occur due to differences in recording methods such as rotating magnetic heads and fixed magnetic heads, or FM modulation recording and AM modulation recording. It can't be helped.

However, even normal audio, which is inferior in sound quality, has a characteristic that the dropout rate is lower than that of high-fidelity audio. Taking advantage of this characteristic, we can replace normal audio with high-fidelity audio at the dropout part of high-fidelity audio. It may be used for Dropout compensation circuit 1 shown in Figure 2
is a method of replacing the dropout part of high-fidelity audio with normal audio, and the output of the normal audio circuit 2 connected to the fixed magnetic head 2a and the output of the high-fidelity audio circuit 3 connected to the rotating magnetic head 3a are as follows. The output of the dropout detection circuit 4 selectively leads to the audio output terminal 7 via an analog switch circuit 5.6 which opens and closes in reverse operation. Since the dropout detection circuit 4 outputs a low level signal when detecting a dropout, the dropout detection circuit 4 is connected to the analog switch circuit 5 provided between the normal audio 2 and the audio output terminal 7 via an inverter circuit 8. output is supplied.

[Problems to be Solved by the Invention] The conventional dropout compensation circuit 1 described above is configured to simply switch the dropout portion to normal audio when a dropout occurs in the high-fidelity audio signal. In the case of normal audio recorded after level correction by an automatic level control circuit (not shown), the signal levels of the level-corrected normal audio and high-fidelity audio do not continue smoothly at the dropout part, causing listeners to On the other hand, there were problems such as the signal level of the reproduced sound changing unnaturally, making it difficult to listen to.

[Means for Solving the Problems] This invention solves the above-mentioned problems.High-fidelity audio and normal audio, which have sound quality differences based on differences in recording methods, are separately supplied for the same audio, and high-fidelity audio and normal audio are supplied separately. a dropout compensation circuit that replaces a dropout portion with normal audio when a dropout occurs in a dropout, the circuit comprising: a level detection circuit that determines the signal level of the high-fidelity audio from a certain level based on a certain level; and a control circuit that allows the replacement if the discrimination result of the level detection circuit is large when the level detection circuit occurs, and mutes the high-fidelity audio if the discrimination result is small. The gist of this is that

[Operation] When a dropout occurs in high-fidelity audio, this invention selects either replacement with normal audio or muting depending on the signal level of the high-fidelity audio immediately before the dropout occurs, and eliminates jarring level fluctuations. Compensate for dropouts that are not accompanied by

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of the dropout compensation circuit of the present invention.

In FIG. 1, the dropout compensation circuit 11 connects a level detection circuit 12 that detects the signal level of the high-fidelity audio to the output line of the high-fidelity audio 3, and combines the output of the level detection circuit 12 with the output of the dropout detection circuit 4. The control circuit 13, which operates according to the output, controls the switching of the analog switch circuits 5 and 6 and the switching of the muting transistor switch Q interposed between the audio output terminal 7 and the ground.

The level detection circuit 12 includes a buffer amplifier circuit 14 connected to the output terminal of the high-fidelity audio circuit 3, and an output terminal of the buffer amplifier circuit 14 connected to a switch 15a and a capacitor C.
The sample and hold circuit 15 samples and holds the sample and hold circuit, a comparison circuit 16 that compares the output of the sample and hold circuit 15 with a preset reference value, and a diode Do connected to the output terminal of the comparison circuit 16. The comparison circuit 16 outputs a high level signal when the output of the sample and hold circuit 15 exceeds the reference value. Switch 15 in sample and hold circuit 15
A is opened by the dropout detection signal of the dropout detection circuit 4, and remains open during the dropout occurrence period, but is otherwise closed.

The control circuit 13 has a Nant gate circuit 17 for switching the analog switch circuit 5.6 and a NOR gate circuit 18 for switching the transistor switch Q, both of which use the output of the level detection circuit 12 as one input. shall be. The NAND gate circuit 17 has the output of the dropout detection circuit 4 inverted in polarity by the inverter circuit 19 as its other input, and the NOR gate circuit 18
uses the output of the dropout detection circuit 4 as the other input.

Now, if no dropout has occurred and the output of the dropout detection circuit 4 is at a high level,
The outputs of the Nant gate circuit 17 and the NOR gate circuit 18 in the control circuit 13 are fixed at high level and low level, respectively, regardless of the output of the level detection circuit 12. Therefore, the analog switch circuit 6 is closed, the analog switch circuit 5 is open, and the transistor switch Q is in the off state.

Therefore, only the output of the high-fidelity audio circuit 3 is guided to the audio output terminal 7 via the analog switch circuit 6.

Here, when the dropout detection circuit 4 detects the occurrence of dropout, its output is supplied to the control circuit 13 as a low level signal. On the other hand, assume that the level detection circuit 12 detects a large signal and outputs a high-level signal immediately before this dropout occurs. in this case,
The output of the Nandt gate circuit 17 in the control circuit 13 is at a low level, and the output of the NOR gate circuit 18 is also at a low level.

Therefore, the analog switch circuit 5 is closed instead of the analog switch circuit 6, but the transistor switch Q remains in the off state. Therefore, instead of the high-fidelity audio in which dropout has occurred, normal audio is led to the audio output terminal 7, and dropout compensation is performed using the normal audio so that the level difference with the signal immediately before dropout does not become harsh.

On the other hand, assume that when the dropout detection circuit 4 detects the occurrence of dropout, the level detection circuit 12 detects a small signal immediately before it and outputs a low level signal. In this case, the output of the NAND gate circuit 17 in the control circuit 13 is at a high level, and the output of the NOR gate circuit is also at a high level.

Therefore, although the analog switch circuit 6 remains closed, which is the same as before the dropout occurred, the transistor switch Q is turned on, and the audio output terminal 7 is grounded and muting is applied. Therefore, in this case, the high-fidelity audio is not replaced by the normal audio, and no dropout compensation is performed that would make the level difference with the signal immediately before dropout unpleasant.

In this way, when a dropout occurs in high-fidelity audio, the dropout compensation circuit 11 adjusts the control circuit 1 according to the signal level of the high-fidelity audio detected by the level detection circuit 12 immediately before the dropout occurs.
3 operates and selects either replacement with normal audio or muting, so even if normal audio is automatically recorded at a constant signal level by the automatic level control circuit at the time of recording, , normal audio is replaced with high-fidelity audio only when there is a large signal, and muted when the signal is small, so loud audio suddenly mixes in when playing at a low volume, eliminating the inconvenience that causes an unnatural and harsh hearing sensation. can be prevented.

[Effects of the Invention] As explained above, according to the present invention, when a dropout occurs in high-fidelity audio, replacement with normal audio or muting is performed depending on the signal level of the high-fidelity audio immediately before the dropout occurs. Since the configuration allows selection of one of the two, even if normal audio is automatically recorded at a constant signal level by the automatic level control circuit during recording, the normal audio will be replaced with high-fidelity audio only when a large signal is detected. Since muting occurs when a small signal is present, it has excellent effects such as being able to effectively prevent the inconvenience that occurs when high-volume audio suddenly mixes in during low-volume playback, resulting in an unnatural and harsh hearing sensation. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a dropout compensation circuit of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional dropout compensation circuit. 2...Normal audio circuit, 3...Hi-fi audio, 4.
... Dropout detection circuit, 5, 6 ... Analog switch circuit, 11 ... Dropout compensation circuit, 12
... Level detection circuit, 13... Control circuit.

Claims (1)

[Claims] A dropout compensation circuit that separately supplies high-fidelity audio and normal audio that have sound quality differences based on differences in recording methods for the same audio, and replaces the dropout portion with normal audio when a dropout occurs in the high-fidelity audio. , a level detection circuit that distinguishes the signal level of the high-fidelity audio from a certain level based on a certain level; and when the dropout occurs, if the determination result of the level detection circuit is high, the replacement is allowed. and a control circuit for muting the high-fidelity audio when the determination result is small.