JPH098755A - Fm stereo receiver - Google Patents

Abstract

PURPOSE: To output a satisfactory sound by attenuating the audio level of a noisy frequency band just for the amount according to a noise level when the detected noise level is higher than a set value. CONSTITUTION: A noise detector 21 detects the noise caused by a multipulse or adjacent interference while being connected to a level meter terminal. When the detected noise is higher than a set level, the audio level of the noisy frequency band is attenuated just for the amount according to the noise level by a DSP 22. Besides, when the noise level is higher than the set level, a prescribed coefficient value is set to the DSP 22 by a microcomputer 23, and the audio level is attenuated just for the amount corresponding to the noise level by the DSP 22. Thus, the noise of the noisy frequency band (from 2kHz to 3kHz) can be reduced, an S/N is improved and the satisfactory sound can be outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM stereo receiver, and more particularly to an FM stereo receiver for controlling the degree of channel separation and the high frequency attenuation of a voice signal according to the electric field strength.

[0002]

2. Description of the Related Art In an FM stereo receiver, the S / N ratio is improved by changing from stereo to monaural or by attenuating (high-cutting) a high frequency range when a weak electric field which causes a large noise level or when each disturbance occurs. You can For this reason,
An on-vehicle radio receiver is provided with a channel separation circuit and a high cut circuit. For example, as shown in FIG. 7, when the received electric field strength becomes E ₁ or less, the degree of channel separation is weakened to give a monaural tendency. , When the received electric field strength becomes E ₂ or less, the high cut amount is increased as the received electric field strength becomes weaker, and the received electric field strength becomes E ₃
When it becomes below, I try to apply soft mute.

[0003]

However, conventionally, the high cut only reduces the sound in the vicinity of 10 kHz, and does not reduce the sound of 2 to 3 kHz which is disturbing to the human ears. Therefore, when the noise level is high, there is a problem that the noise in the sound range is audible.
There is also a problem that the high-cut amount becomes large and a high-fidelity feeling cannot be obtained. From the above, an object of the present invention is to provide an FM stereo receiver capable of outputting a good sound by attenuating an audio level in a frequency band in which noise is offensive by an amount according to the noise level when the noise level is equal to or higher than a set value. Is to provide.

[0004]

According to the present invention, there are provided means for detecting a noise level and determining whether or not the noise level is equal to or higher than a set value, and in the case where the noise level is equal to or higher than the set value. The FM stereo receiver is provided with means for attenuating an audio level in a frequency band in which noise is annoying, according to the noise level.

[0005]

[Function] The noise level is detected, and it is determined whether or not the noise level is equal to or higher than the set value. When the noise level is equal to or higher than the set value, the audio level in the frequency band in which noise is annoying is adjusted according to the noise level. , Attenuate. In this way, noise in the frequency band where noise is offensive can be reduced, and good sound can be output.

[0006]

1 is a block diagram of an FM stereo receiver according to an embodiment of the present invention. In the figure, 11 is an antenna, 12 is a front end, 13 is an intermediate frequency amplifier, 14 is a detector,
Reference numeral 15 is a noise killer, 16 is a stereo demodulation circuit, and 17 is a separation control unit for weakening the degree of separation and making a monaural tendency as shown in FIG. 7 when the received electric field intensity becomes E ₁ or less. , 18 has a received electric field strength of E
_When it becomes ₂ or less, as shown in FIG. 7, a high cut circuit that increases the amount of high frequency attenuation (high cut amount) as the received electric field strength becomes weaker, 19 is a source switching unit, 20 is a level meter of the intermediate frequency amplifier 13. A level meter circuit connected to the terminal for outputting a level meter signal Ve having a value corresponding to the received electric field strength E, and 21 a noise detecting circuit,
It is connected to a level meter terminal to detect noise due to multipath or adjacent interference. The direct current component appearing at the level meter terminal contains an AM component proportional to noise due to multipath and adjacent interference.
Noise can be detected using the M component. Reference numeral 22 is a digital signal processor (DSP), which attenuates the audio level in the frequency band (2 to 3 KHz) where noise is annoying when the noise level is higher than the set level, and 23 is a microcomputer When the noise level is equal to or higher than the set level, a predetermined coefficient value is set in the DSP and the DSP attenuates the audio level by an amount according to the noise level.

FIG. 2 is a block diagram of a noise detection circuit 21 for detecting adjacent interference. Intermediate level amplifier 13 level meter
A high-pass capacitor 21a for passing a high frequency component of a signal appearing at the terminal, a tuning amplifier 21b having a tuning tank STK having a tuning frequency of around 100 kHz and amplifying and outputting an adjacent interference component near the tuning frequency, and an adjacent interference. The detector 21c which converts a signal into direct current is provided.

FIG. 3 shows an unpleasant frequency band (2 to 3 kHz).
z) is a functional block diagram of a DSP that attenuates the audio level, and is a 1-sampling time delay unit 31a to 31.
d and predetermined coefficients a ₀ , a ₁ , for the input signal and each delayed signal,
has a _2, b _1, b ₂ a multiplication unit 32a~32e for multiplying, summing unit 33 for adding and outputting the multiplication unit output. By appropriately setting the coefficients a ₀ , a ₁ , a ₂ , b ₁ and b ₂ , the dip characteristic DP in the band F as shown in FIG.
Can be provided to control the depth (attenuation amount) of the dip. As the noise level increases, the amount of attenuation increases as indicated by the dotted line.

FIG. 5 is a correspondence table of the noise level and the coefficient. The noise level is divided into three stages of large, medium and small, and the coefficients a ₀ and a ₁ are obtained so that the attenuation amount corresponding to each noise level can be obtained. , A ₂ , b ₁ , b ₂ have been determined.
This correspondence table is preset in the microcomputer 23.

FIG. 6 is a processing flow of the microcomputer 23.
The microcomputer 23 AD-converts and takes in the noise level detected by the noise detection unit 21 (step 101),
It is checked whether the noise level is higher than a preset value (step 102), and if it is lower, the same channel separation control, high cut control and soft mute control as before are performed to improve the S / N ratio. If the noise level is lower than the preset value, the DSP 22 does not attenuate the audio level in the frequency band (2 to 3 kHz). However, when the noise level is equal to or higher than the set value, the coefficient value corresponding to the noise level is obtained from the table (FIG. 5) and set in the DSP 22 (step 103). As a result, the DSP 22 attenuates the audio level in the frequency band (2 to 3 kHz) where noise is annoying, and outputs the attenuated audio level. This makes it possible to simultaneously reduce noise in a frequency band where noise is annoying, improve the S / N ratio, and output good sound. Although the present invention has been described above with reference to the embodiments, the present invention can be variously modified according to the gist of the present invention described in the claims, and the present invention does not exclude these.

[0011]

As described above, according to the present invention, the noise level is detected, and it is determined whether or not the noise level is equal to or higher than a set value. Since the audio level is attenuated by an amount corresponding to the noise level, noise in the frequency band where noise is annoying can be reduced, and the S / N ratio can be improved to output a good sound.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an FM stereo receiver of the present invention.

FIG. 2 is a configuration diagram of a noise detector.

FIG. 3 is a functional block diagram of a DSP that attenuates a predetermined frequency band.

FIG. 4 is an explanatory diagram of effects on a DSP frequency band.

FIG. 5 is a correspondence table of noise levels and coefficient values.

FIG. 6 is a processing flow of a microcomputer.

FIG. 7 is an explanatory diagram of high cut and channel separation.

[Explanation of symbols]

 18. High-cut circuit 20. Level meter 21. Noise detector 22. DSP 23 .. Microcomputer

Claims (1)

[Claims] 1. An FM stereo receiver that controls the degree of channel separation and the amount of high-frequency attenuation of a voice signal according to the electric field strength, detects a noise level, and determines whether the noise level is equal to or higher than a set value. An FM stereo receiver comprising means and means for attenuating an audio level in a frequency band where noise is annoying when the noise level is equal to or higher than a set value, by an amount according to the noise level.