JPS61190762A - Recorder of audio signal - Google Patents

Abstract

PURPOSE:To obtain an audio signal being applied normally with noise reduction, at reproduction, by eliminating this part in advance by a limitter, in case there is a part exceeding the maximum permissible input level of an A/D converter to an audio input signal, at recording. CONSTITUTION:In a signal line between a filter 13 and a noise reduction circuit 14, a limiter 3 to limit the level of a signal Sa at the level corresponding to the maximum permissible input level of the A/D converter 15. In such a way, at recording, when the audio signal Sa is fetched from the filter 13, after the signal Sa is limited to the maximum permissible input level of a converter 15 by a limiter 31, and supplied to a noise reduction circuit 14 in the output signal Sn, there is not the part exceeding the maximum permissible input level of an A/D converter 24. In such a way at reproduction, the audio signal Sa that the noise reduction is normally applied can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to, for example, a digital recording device for audio signals.

[Summary of the invention]

According to the present invention, when an audio signal is digitally recorded in, for example, 8 mm video, the level of the audio signal is limited to prevent a reproduction noise reduction circuit from malfunctioning.

[Conventional technology]

The recording and reproducing systems of the PCM audio signal system for 8 mm video are configured as shown in FIGS. 3 and 4, for example.

That is, during recording, the audio signal (stereo signal) Sa is supplied from the input terminal (11) through the input amplifier (12) to the low-pass filter (13), and unnecessary high-frequency components (components higher than the horizontal frequency of the video signal) are removed. is removed, and this signal Sa is supplied to a recording noise reduction circuit (14), and the amplitude is compressed with predetermined characteristics to become an audio signal Sn. This signal Sn is input to an A/D The signal is supplied to a converter (15) and sampled at twice the horizontal frequency to produce a digital signal Sd. Then, this signal Sd is sent to the encoder (
16), the time axis is compressed by about 6 times for each field period, and encoded into a signal Se with an error correction code added, and this signal Se is supplied to the modulation circuit (1
7) and is converted into a pi-phase mark signal sb, and this signal sb is supplied to a pair of rotating magnetic heads (11) through a recording amplifier (18).

This head (1) has an angular spacing of 180° from each other, is rotated at a frame frequency, and covers an angular range of approximately 220° with respect to its rotating circumference.
) is wound diagonally and run at a constant speed. Therefore, as shown in FIG. 5, a diagonal magnetic track (3) is formed on the tape (2) every one field period, and its 40° overlamp section (3A)
The signal sb is recorded in a section of about 30 degrees. Although not shown, a video signal recording system records a video signal in a 180° section (3v) of the track (3), and the entire length of the track (3) is used for tracking servo during playback. pilot signals are recorded simultaneously.

On the other hand, during re-going, the head (1) reproduces the signal sb from the tape (2), and this signal sb is transmitted to the demodulation circuit (22).
) and demodulated into a signal Ss, this signal Se is supplied to a decoder (23) and decoded into a signal Sd that has undergone error correction and error correction, and this signal Sd is
It is supplied to a converter (24) and converted into a signal Sn,
This signal Sn is supplied to a reproduction noise reduction circuit (26) through a low-pass filter (25), and the noise reduction circuit (14) processes the complementary characteristics to generate the original audio signal Sa, and this signal Sa is output. It is taken out to an output terminal (28) through an amplifier (27).

(Literature: "Radio Technology J March 1985 issue, published by Radio Technology Co., Ltd.") [Problems to be solved by the invention] By the way, the input/output characteristics of the recording noise reduction circuit (14) are also shown in Figure 6. As shown, its input signal S
The input/output characteristics of the reproduction noise reduction circuit (26) are such that the changes in the level (amplitude) of the input signal Sn are doubled. be.

During recording, a sine wave signal whose level changes from 0 to medium (-10 dB) to small (-30 dB) is supplied to the noise reduction circuit (14) as the input signal Sa, as shown in FIG. 7A, for example. Then, the response of the noise reducer 5 circuit (14) has a time constant and is influenced by the signal level just before that, so the output signal Sn changes as shown in FIG. That is, the level of signal Sn is
During the period T2 (attack time), the uncompressed level (-) is influenced by the level of the signal Sa during the period T1.
10 dB) to a normal level (-5 dB), and remains at the normal level during period T3. Then, during period T4 (recovery time), the reliability% of period T3 is
Overly compressed level affected by the level of Sa (-2
5 dB), it gradually returns to the normal level (-15 dB), and stabilizes at the normal level in period T5.

On the other hand, during playback, this level-compressed signal Sn is
Since it is supplied to the noise reduction circuit (26) and level expanded with complementary characteristics, the output signal Sa becomes as shown in A in the same figure, that is, the original audio signal Sa
is obtained.

However, if a signal Sa as shown in FIG. 8A is supplied to the noise reduction circuit (14) during recording, a problem will occur during reproduction.

That is, when such a signal Sa is supplied to the noise reduction circuit (14) during recording, the output signal Sn is level-compressed as shown in FIG. 8B in the same way as in the case of FIG. 7. This signal Sn is then supplied to the next stage A/D converter (15), but in any A/D converter, as the level (instantaneous level) of the analog input signal increases, it reaches a certain level. In this case, the digital output signal becomes all “1”, and even if the analog input signal is raised to a higher level, the digital output signal becomes all “1”.
In other words, for any A/D converter, there is a clear maximum allowable input level (the upper limit of the dynamic range), and input levels above this level will cause clipping in the output. become.

In the case of 8 mm video, the OdB level of the signal Sn is set to the maximum allowable level of the A/D converter (15), as shown by the chain line in FIG.
In the /A converter (15), the part of the signal Sn that is more than OdB is clipped, and the digital signal Sd of the A/D conversion (shown after D/A conversion) is the part that is more than OdB as shown in C of the same figure. A portion of the signal is lost due to clipping.

Then, since such a signal Sd is recorded and reproduced, the signal Sn from the D/A converter (24) becomes a signal with more than OdB clipped as shown in C of the same figure. When the signal Sn is supplied to the noise reduction circuit (26), compared to the signal Sn at the time of recording (B in the same figure), the part that is more than OdB has disappeared.
The signal Sa from the noise reduction circuit (26) is converted into the original audio signal Sa (A in the same figure), as shown in the same figure.
), the level of the signal during the period T4 is attenuated compared to the period T4. That is, during recording, the audio signal Sa is
If there is a portion that exceeds the maximum allowable input level (non-clip input level) of the A/D converter (15), during playback, the level of the following signal portion (period T4) will be lower than the original level, and thereafter (period Ts ) becomes the original level.

In general, if the audio signal is a normal music signal, clipping in the signal does not cause much of a problem in terms of hearing, but if there is a partial attenuation of the level as in period T4, it becomes unpleasant to listen to. It becomes.

This invention attempts to solve these problems.

Means for Solving Problem C] In the present invention, for example, the signal line between the filter (13) and the noise reduction circuit (14) is
a limiter (31) that limits the level of the signal Sa at a level corresponding to the maximum allowable input level of the /D converter (15);
) will be established.

[Effect]

According to this invention, when recording, the audio signal Sa is
Even if there is a part that exceeds the maximum allowable input level of the D converter (15), it is removed by the limiter (31) before noise reduction processing and A/D conversion for recording are performed, so that it will not work normally during playback. An audio signal Sa subjected to noise reduction can be obtained.

Furthermore, the configuration for this purpose is extremely simple and low cost, as it only requires the provision of a limiter (31).

〔Example〕

That is, as shown in FIG. 1, in the signal line between the filter (13) and the noise reduction circuit (14),
A limiter (3) limits the level of the signal Sa at a level corresponding to the maximum allowable input level of the A/D converter (15).
1) will be provided.

According to such a configuration, when recording, FIG. 2A (FIG. 8A)
When a signal Sa as shown in Figure B) is extracted from the filter (13), this signal Sa is
The limiter (31) limits the input level to the maximum allowable input level (OdB) of the A/D converter (15) before supplying it to the noise reduction circuit (14), so the output signal Sn becomes as shown in Figure C. , A/D converter (
24) will not exceed the maximum allowable input level.

Therefore, when this signal Sn is recorded and played back, D
/A converter (26) also outputs the signal Sn of C in the same figure.
Therefore, as shown in the same diagram, the noise reduction circuit (26) obtains an audio signal Sa in which only the portion above OdB is clipped, and the other portions are reproduced normally. . Note that this signal S
As mentioned above, the clip part a does not have much of an audible problem.

Thus, according to the present invention, even if there is a portion of the audio signal Sa that exceeds the maximum allowable input level of the A/D converter (15) during recording, this portion is removed by the limiter (31) before being processed for recording. Since noise reduction processing and A/D conversion are performed, it is possible to obtain an audio signal Sa that has undergone normal noise reduction during playback.

Furthermore, the configuration for this purpose is extremely simple and low cost, as it only requires the provision of a limiter (31).

Note that in the above description, the limiter (31) can be configured with a constant voltage diode, a differential amplifier, or the like. In addition, the limiter (31) is connected to the terminal (11) and the filter (1).
3).Furthermore, for 8 mm video, the audio signal Sa is subjected to noise reduction processing for recording and then converted to an FM signal.
This FM signal is frequency-multiplexed with the video signal and the head (1
1, it is recorded on tape (2), but in this case too, if there is an excessive input part in the audio signal Sa during recording, the FM signal will be overmodulated, and the same problem as mentioned above will occur during playback. This invention can be used to solve such problems.

Furthermore, as proposed in Japanese Patent Application No. 57-15287, it can also be applied to the case where the track (3) is divided into a plurality of sections in the length direction and the signal sb is recorded and reproduced in these divided sections. .

Furthermore, noise reduction circuits (14) and (2
The input/output characteristics of 6) are also not a concern.

〔Effect of the invention〕

According to this invention, when recording, the audio signal Sa is
Even if there is a portion that exceeds the maximum allowable input level of the D converter (15), it is removed by the limiter (31) before noise reduction processing and A/D conversion for recording are performed, so that the input level is not exceeded during playback. , it is possible to obtain an audio signal Sa that has undergone normal noise reduction.

Furthermore, the configuration for this purpose is extremely simple and low cost, as it only requires the provision of a limiter (31).

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an example of the present invention, and FIGS. 2 to 8 are diagrams for explaining the same. (11 is a rotating magnetic head, and (2) is a magnetic tape. Figure 2: Frozen form of each egg. Distance engraving of each part.

Claims (1)

[Claims] An input audio signal is supplied to a noise reduction circuit for recording to compress level changes, and the audio signal from this noise reduction circuit is processed to the maximum allowable level, such as a D/A converter or an FM modulation circuit. In an audio signal recording device that supplies the signal to a conversion circuit whose input level is set, converts it into a signal of a predetermined format, and records the converted signal, the input end of the input audio signal and the 1. An audio signal recording apparatus, comprising: a circuit for limiting the level of the audio signal supplied to the conversion circuit so as not to exceed the maximum allowable input level, on a signal line between the recording noise reduction circuit and the recording noise reduction circuit.