JPS634267B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reproduction audio time axis processing circuit for a variable speed reproduction device.

More specifically, the present invention provides a circuit suitable for use when applying an audio time-base companding circuit to a VTR device having a variable speed playback function or a stereo recording and reproducing device having a variable speed playback function. It is something to do.

Recent home VTR devices are required not only to simply record and playback, but also to have various other functions. Among these, special playback functions include, for example, still image playback, high-speed image search, and variable speed playback functions. The quality of images during these special reproductions has significantly improved due to advances in reproduction technology. On the other hand, regarding reproduced audio, in most special reproductions, muting is applied to the audio signal output due to the reproduction processing procedure, but in the case of variable speed reproduction, the reproduced sound is output as is. In variable speed playback of an audio signal recorded on a magnetic recording tape, the overall frequency band of the reproduced audio signal changes depending on the ratio of the playback speed during normal playback and the playback speed during variable speed playback. . In other words, when playing quickly, the reproduced audio frequency increases as a whole, and when playing slowly, the frequency changes to lower overall. When the variable range is narrow, intelligibility is not significantly impaired and there is no practical problem, but recent home VTRs
The variable range extends from a paused state to about 1.4 times the normal playback speed, and the intelligibility of the audio signal output as it is is significantly reduced, which is a practical difficulty. Therefore, compression and expansion processing is performed on the time axis of the reproduced audio signal for variable speed playback, so that the playback speed remains fast or slow, and at the same time, the frequency of the reproduced audio is converted to the same band as during normal playback. , it is thought that good intelligibility can be obtained during all variable speed playback.

The present invention provides a time-base companding processing circuit for such audio.
The present invention aims to provide a circuit suitable for application to VTR equipment, and in particular provides an application example where the VTR equipment has a variable speed playback function and is also compatible with audio multiplex broadcasting. be. The present invention will be described in detail below along with Examples.

When applying an audio time axis companding circuit to a VTR compatible with audio multiplex broadcasting, a problem arises when playing back stereo audio. Two expansion circuits must be used to add to each channel CH. However, the cost of the time axis companding circuit itself occupies a large proportion of the total cost of the VTR, and using two of these expensive time axis companding circuits poses a major problem.

On the other hand, if we consider the purpose of the variable speed playback function,
What is required of the reproduced audio at this time is good intelligibility; for example, the requirements for stereophonic sound effects and fidelity are far lower than the requirements for intelligibility. The present invention takes this point into consideration, and in the case of variable speed playback of stereo signals, one time axis is set for a monaural signal which is the sum of the signals of both (L) and (R) CHs, without sacrificing practical value. It is configured so that processing is performed by a companding circuit.

The drawings are examples illustrating the content of the present invention.
The VTR has left and right playback heads PH(1) and PH(r).
The playback signal from the audio playback circuit 1 is (L) (R)
These two systems are input to the output switching circuit 2.
(Lch) output signal is interlocked with selector switch S1,
It is connected to the main CH contacts 3 and 4 of S2 and the stereo/double contact 5 of S1, and the output signal of (Rch) is connected to S1,
It is connected to the sub-CH contacts 6 and 7 of each S2 and the stereo/double contact 8 of S2. Lord of S1 and S2
When CH contacts 3 and 4 are closed, S1 and S
2. (Lch) audio is simultaneously output to each common terminal 9, 10, and when sub-CH contacts 6, 7 are closed, (Rch) audio is simultaneously output to common terminals 9, 10. be done. Also S1,
When the respective stereo/duplex terminals 5 and 8 of S2 are closed, (Lch) playback audio is output to the common terminal 9 of S1, and (Rch) playback is output to the common terminal 10 of S2. Audio is output.

Changeover switches S3, S4, S5, S6 are for VTR
This is a signal path changeover switch that is interlocked (or controlled) by the variable speed regeneration start switch circuit 11, and in the case of normal regeneration, it is normally closed (N.
C) Terminals 12, 13, 14, 15 are closed, and the output signal from the output switching circuit 2 is transmitted from the common terminals 18, 19 of S3, S4 to the NC terminals 12, 14 and 13, 15 of S5, S6. common terminal 16,
17 is output as is. Normally open (NO) terminals 20 and 21 of S3 and S4 are connected to the input of a signal addition circuit 22. The signal addition circuit 22 outputs a sum signal of the two input signals to the audio time-base companding circuit 23. The time axis companding circuit 23 responds to the speed signal from the tape speed detection circuit 24 by expanding the time axis for high speed playback and compressing the time axis for low speed playback. Converts the frequency band of the reproduced audio to the same frequency band as the original sound for normal reproduction. Note that a VTR motor servo circuit can be used as the tape speed detection circuit 24, and the motor feed voltage can be used as the speed signal. The output of the audio time axis companding circuit 23 is S5, S
It is connected to the NO terminals 25 and 26 of 6.

Next, the switch circuit 11 is closed, and at the same time the variable speed regeneration operation starts, S3, S4, S5, S6
The NO terminal side of is closed, and as described above, the two systems of reproduced audio are converted into a sum signal by the signal adder 28, subjected to time axis compression or expansion processing, and then output.

The variable speed playback start switch circuit 11 may be controlled by the tape speed detection circuit 24 as shown in the figure, but it is also possible to control the opening and closing of S3, S4, S5, and S6 by manual means unrelated to the detection circuit 24. It's okay to get old.

Further, as is clear from the content thereof, the present invention can also be applied to a stereo recording/playback device capable of variable speed playback.

As described above, the present invention is configured such that even if the reproduced signal from the output switching circuit is a stereo signal during variable speed reproduction, the signals are added to form a monaural signal, and the time axis companding process is performed on this monaural signal. Variable speed playback is low cost and highly practical.
A VTR device or a stereo recording/playback device can be realized.

[Brief explanation of the drawing]

The drawing is a block circuit diagram showing a reproduced audio time axis processing circuit of the present invention. 1...Audio reproduction circuit, 2...Output switching circuit, 1
1... Variable speed playback start switch circuit, 22... Signal addition circuit, 23... Time axis companding circuit, 24...
Tape speed detection circuit, S3, S4, S5, S
6...Signal changeover switch.

Claims (1)

[Claims] 1. A variable speed playback operation detection means for detecting the presence or absence of a variable speed playback operation, a signal addition circuit that adds two input audio signals, and a time axis of the added signal of the signal addition circuit to adjust the playback speed during variable speed playback. a time-base companding circuit that compresses and expands as appropriate according to the speed, and a time-base companding circuit that is controlled by the variable speed playback operation detection means and outputs the two input audio signals corresponding to each other during an operation other than the variable speed playback operation. and a signal path switching means for supplying the two input signals to the signal addition circuit during variable speed playback and simultaneously connecting the output of the time base companding circuit to the two output terminals. Playback audio time axis processing circuit of variable speed playback device.