JPH0739090Y2 - Sound quality improvement circuit - Google Patents

Description

Detailed Description of the Invention (a) Field of Industrial Application The present invention relates to a sound quality improvement circuit.

(B) Conventional technology In order to improve the sound quality of a video tape recorder (VTR), a method of recording an audio signal with a rotary head by an FM modulation method has been realized (for example, TV technology '84 .8 August PP.27-32). reference). In this method, an audio signal to be recorded is subjected to a predetermined noise reduction process and supplied to an FM modulation circuit via a limiter circuit for preventing overmodulation.

(C) Problems to be solved by the invention By the way, in the case of an audio signal, a high-level signal may be suddenly input (such as the sound of a drum set cymbal). In this case, the noise reduction (N
R) The processed signal is recorded with its amplitude limited by a limiter provided in the preceding stage of the FM modulation circuit in order to prevent overmodulation. Therefore, a signal having a large level and a short period is distorted by being applied to a limiter or by NR processing during reproduction.

(D) Means for Solving the Problems In the present invention, a level detection circuit for detecting that the output of the NR circuit during recording exceeds a predetermined value, and a signal of a predetermined pulse width based on the output of the level detection circuit A pulse output circuit for outputting and a means for increasing the compression rate of the NR circuit during the output period of the pulse signal are provided.

(E) Action Therefore, since the impulse-like audio signal is compressed as a whole without being limited, the waveform distortion can be reduced as compared with the conventional example.

(F) Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment, and FIGS. 2 and 3 are waveform diagrams.

In the figure, (1) is a modulation / demodulation IC, (2) is an NR IC,
(3) and (4) are level detection circuits (corresponding to L and R channels), and (5) is an IC having two monomultis.
The NR IC (2) (compatible with L and R channels) conforms to the VHS standard, and at the time of recording, the input terminal (2a)
A predetermined compression enhancement process is applied to the audio signal input to the. Then, the output signal after this processing is input to the modulation / demodulation IC (1) (having a built-in limiter) and is also supplied to the level detectors (3) and (4).

The level detector (3) (hereinafter, the L channel will be described) has two comparators. Then, when a large-amplitude audio signal exceeding the upper and lower limit voltage range defined by the resistors (R ₁ ) (R ₂ ) (R ₃ ) is obtained, an output (L level) is obtained. ing. The upper and lower limit voltages correspond to the limiter level of the modulation / demodulation IC.

The output of the level detector (3) changing to the L level triggers the mono-multi (provided in the IC (5)),
A pulse signal that is at H level for a predetermined period is output. This is to create a pulse whose compression rate can be changed.
This predetermined period is determined by listening,
In the embodiment, it is about 0.5 to 1 ms. It should be noted that this mono-multi can be re-triggered (it can be used when impulse-like signals are obtained at short intervals).

This mono-multi output is an IC for NR through a diode (D ₇ ).
It is given to the smoothing capacitor (C0) of the level detector (2b) of (2). The degree of compression is controlled according to the voltage of this capacitor (C0) (10 μF). When the output from the monomulti is obtained, the compression rate becomes large and the amplitude of the audio signal is suppressed below the limiter level. Will be done.

Therefore, the recorded signal is less likely to be clipped by the limiter, and the degree of waveform distortion is reduced. The effect of the present invention will be described with reference to FIGS.
FIG. 2 shows the output waveform of the NR circuit ((a) Conventional example (b) embodiment), and FIG. 3 shows the final reproduction output waveform ((b) Conventional example (b) embodiment). There is.

The input signal was a 400 Hz square wave. This is because it is considered that the square wave can estimate the impulse-like distortion of the audio signal.

As shown in FIG. 2, in the case of the embodiment, the level of overshoot (generated by emphasis) at the time of rising and falling becomes small, and the limiter level is not reached. In the conventional case, the reproduced signal is clipped by the limiter, and the waveform is blunted by NR (de-emphasis etc.) at the time of reproduction, resulting in poor crispness of the reproduced signal.
On the other hand, according to the embodiment, the waveform distortion is reduced as shown in FIG.

(G) Effect of the Invention As described above, according to the present invention, the waveform distortion during reproduction can be reduced, which is practical.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the embodiment, FIG. 2 and FIG.
The figure is a waveform diagram. (2) …… NR circuit, (3) (4) …… Level detection circuit (5) …… Monomulti (pulse output circuit) (C ₀ ) (C ₀ ) ′ …… Smooth capacitor

Claims (1)

[Scope of utility model registration request] 1. A level detection circuit for detecting that the output of an NR circuit during recording is a predetermined value or more, a pulse output circuit for outputting a pulse signal of a predetermined pulse width based on the output of the level detection circuit, and this pulse. A sound quality improvement circuit comprising means for increasing the compression ratio of the NR circuit during a signal output period.