JPS6233666B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio reproduction circuit, and is intended to alleviate the difficulty of listening due to dropouts of reproduced audio.

When reproducing audio information stored on a recording medium, for example, when extracting and reproducing an audio signal from a video signal and an audio signal that have been frequency multiplexed and recorded on the same track, dirt or other deposits may occur on the recording medium. If there is such a problem, periodic dropouts occur, making it difficult to hear the reproduced audio. One way to solve this problem is to cut off the transmission of audio information for the entire dropout period, taking into consideration that the period during which dropouts occur is generally short. This method is effective as long as the period during which dropouts occur is short, but when the period becomes long, it becomes difficult to grasp the content.

The present invention has been devised in view of this point, and it reduces the clarity of the audio signal reproduced over the entire period during which periodic dropouts occur, thereby alleviating the difficulty of listening due to the dropouts, while at the same time The aim is to make it possible to understand the contents of the book.

FIG. 1 shows an embodiment of the invention. Pickup 1 was stored in frequency multiplex format from the recording medium.
Reproducing and extracting FM video signals and FM audio signals. The reproduced FM signal (FIG. 2) passes through a preamplifier 2 and is then supplied to a video processing circuit 3, an audio processing circuit 4, and a dropout detection circuit 5. The video processing circuit 3 processes the FM video signal and derives as its output a video signal capable of displaying an image on the screen of a standard television receiver. The dropout detection circuit 5 detects the periodic dropout DO included in the reproduced FM signal and generates a dropout detection signal ( _second Figure) is output. This period T ₂
is 1/30 second for the above recording medium that stores one frame of video information per revolution,
The detection signal can be easily obtained by providing in the detection circuit 5 a monostable multivibrator that is retriggered when a dropout pulse is present with a cycle within this time.

The audio processing circuit 4 includes a filter 6 and a limiter 7.
It includes an FM demodulation circuit 8 and an amplifier 9 whose transmission characteristics are controlled based on the dropout detection signal. As shown in Fig. 2, the output of the FM demodulation circuit 8 has periodic large signal distortions in response to the dropouts of the reproduced FM signal (Fig. 2), and if this signal is fed as is to the speaker, the reproduced sound will be unnatural. However, in the present invention, the transmission characteristics of the amplifier 9 are corrected during this dropout occurrence period, that is, the level and/or frequency characteristics of the reproduced audio signal are corrected so as to alleviate the ambiguity caused by the dropout. This is an attempt to eliminate this drawback.

Figures 3 to 7 show different embodiments of amplifiers having this correction function, and Figures 3 and 4 are examples in which the amount of negative feedback is increased when a dropout detection signal is present to reduce the amplification degree of the amplifier. 5 and 6 are designed to degrade the high frequency characteristics of the amplifier. Further, FIG. 7 shows a combination of both methods. As shown in FIG. 8, the frequency characteristics of the amplifier shown in each of these figures are as follows:
The one in FIG. 4 has characteristic B, the one in FIGS. 5 and 6 has characteristic C, and the one in FIG. 7 has characteristic D. In FIGS. 3 to 7, 10 is a de-emphasis circuit, Q ₁ and Q ₂ are transistors that constitute the amplifier 9, and Q ₃ , Q ₄ , Q ₅ , Q ₆ , Q ₇ , and Q ₈ are dropout detection signals (the first This is a switching transistor arranged to be conductive only when the condition shown in FIG. 2) is present.

When the output of the FM demodulation circuit 8 (Fig. 2) is applied to the amplifier 9 shown in Fig. 7, for example, the entire output level is adjusted as shown in Fig. 2 only during the period when the dropout detection signal (Fig. 2) exists. approximately
It is possible to lower the dropout by 6 dB and to dull the waveform at the boundary between the signal and the dropout, thereby alleviating the difficulty of hearing the reproduced audio.

In the system for transmitting audio signals reproduced from a recording medium, the present invention provides a system for transmitting audio signals reproduced from a recording medium, when there is a periodic dropout in the reproduced audio signal. Since an amplifier is provided to correct the frequency characteristics so as to alleviate the unintelligibility caused by the dropout, it is possible to alleviate the difficulty in hearing the reproduced audio caused by the periodic dropout, and also to reduce the difficulty in hearing the reproduced sound caused by the periodic dropout. Unlike the prior art in which the reproduced audio signal is cut off, there is no risk of hindrance in grasping the contents of the period.

[Brief explanation of the drawing]

Figure 1 is a configuration block diagram of a video player having an audio playback circuit according to the present invention, Figure 2 is a waveform diagram, Figures 3 and 4 are actual circuit diagrams of an amplifier with a level correction function, and Figures 5 and 6. 7 is an actual circuit diagram of an amplifier having a frequency characteristic correction function, FIG. 7 is an actual circuit diagram of an amplifier having a level and frequency characteristic correction function, and FIG. 8 is a frequency characteristic diagram of the amplifier. 4... Audio processing circuit, 5... Dropout detection circuit, 9... An amplifier (correction circuit) having a level and/or frequency characteristic correction function.

Claims (1)

[Claims] 1. When there is a periodic dropout in the reproduced audio signal in a system that transmits the audio signal reproduced from the recording medium, the level and/or frequency characteristics of the reproduced audio signal shall be adjusted to the level and/or frequency characteristics of the reproduced audio signal during the entire period during which the dropout exists. An audio reproduction circuit comprising a correction circuit that corrects to alleviate ambiguity caused by.