JPS62145935A - Reproduced sound field correction circuit at multi-path disturbance - Google Patents

Abstract

PURPOSE:To obtain a reproduced sound field stable even at multi-path fading by providing a sound field correction circuit restoring the location of a sound image to the home position again when the position of the sound image is about to change. CONSTITUTION:A part of left and right signal components is given to high pass filters 11, 12 whose cut-off frequency is nearly 3kHz, only the intermediate and high frequency components are inverted by inverting circuits 13, 14 and the result is fed respectively to the right and left signal components. Thus, the inverted phase of the right signal component is fed to the left signal output and the inverted phase of the left signal component is fed to the right signal output. Thus, the inverted component moves the left sound source to the left and the right sound source to the right, and even when the high-cut and blending are applied at multi-path fading so as to generate a stable reproduced sound field.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a reproduced sound field correction circuit for a vehicle-mounted FM receiver in the event of multipath interference.

B0 Summary of the Invention In a system that performs high cut and blend operations when multipath fading occurs, when the position of the sound image changes in response to this multipath fading, the mid-high frequency signal of the right signal component is inverted to the left signal component of the audio signal. Playback sound field correction in the event of multipath interference by adding the mid-high frequency signal of the left signal component to the right signal component in reverse phase, moving the left sound source further to the left and the right sound source further to the right. circuit.

C1 Conventional technology In-vehicle FM reception i is affected by multipath fading that causes amplitude fluctuations according to the Lehre distribution lawF
When receiving an M broadcast, strong noise occurs in the demodulated output, and the reception quality deteriorates significantly. In order to reduce this noise, in-vehicle FM receivers have attempted to improve the S/N ratio by using so-called high-cut and blend functions that automatically control the sound quality and sound field in response to multipath fading. However, since this function controls the sound quality and the sound field, there is a drawback that the sound image in the reproduced sound field constantly changes depending on the control conditions, which tends to result in an unstable sound field.

One aspect of human binaural auditory perception is the ability to localize the direction of a sound source, and it is said that humans determine the direction of a sound source based on the level difference, phase difference, and time difference between the sound pressures applied to the two ears. Directional localization ability is related to the sound pressure level difference between the left and right ears for high frequency components, and is related to the phase difference between the left and right ears for low frequency components.

Blending operations in response to multipath fading result in constant changes in the degree of separation of the stereo signals. As a result, the position of the sound image constantly changes due to changes in the sound pressure levels output from the left and right speakers, resulting in an unstable sound field. In other words, when the degree of separation changes due to the blending operation, as shown in Figure 4, the sound image in the right direction constantly moves between the right speaker SPR and the center position A, and the sound image in the left direction constantly moves between the left speaker SPL and the center position A. It will change. When the degree of separation becomes O (monaural reception), the sound pressure levels output from the left and right speakers are equal, so the sound image moves to the center position A and is localized to the center.

Furthermore, due to the high-cut operation, high frequency components are attenuated, and the decrease in the sound pressure level of the left and right speakers SPR and SPL is equivalent to the sound image becoming more distant. In other words,
In FIG. 4, the position of the sound image has moved away from A to B.

If the high-cut and blending operations are performed frequently due to multipath fading, the position of the sound image will constantly change, resulting in a reproduced sound field that is extremely uncomfortable for the listener O. In particular, multipath fading causes rapid changes in the position of the sound image because the high frequency components have short periods.

D0 Problems to be Solved by the Invention As described above, if high cut and blend operations are performed in response to multipath fading, the position of the sound image changes, resulting in an unstable reproduction sound field.

Therefore, if the position of the sound image is about to change due to high-cut and blending operations, if it can be returned to its original position, an unstable reproduction sound field will not result. In other words, as shown in Figure 4, the speaker SPR and SPL
When the sound source at the position deteriorates in separation due to the blending operation and attempts to move to point A, the speaker S P
By returning the sound sources to the R and SPL positions, the reproduced sound field becomes stable and a reproduced sound field with a three-dimensional effect becomes possible.

Therefore, an object of the present invention is to provide a reproduction sound field correction circuit that can suppress changes in the position of a sound image as much as possible and create a stable reproduction sound field even when performing high cut and blend operations during multipath fading. It is to be.

E6 Means for Solving Problems In order to achieve the above object, the present invention provides a control voltage circuit that generates high-cut and blend control voltages for a stereo demodulation circuit using a reproduced sound field correction circuit signal meter voltage at the time of multipath disturbance. , a low-pass filter (hereinafter abbreviated as LPF in this specification) means for removing the dip voltage of the signal meter, and a reverse phase component of the middle and high frequency components of the right signal output is added to the left signal output, and the right signal A voltage generated by a sound field correction means that adds an inverse phase component of the middle and high range components of the left signal output to the output, a means for generating a switching signal for the sound field correction means, and a means for removing the control voltage and the dip voltage. and comparing means for issuing a control signal to the means for generating the switching signal based on the comparison of the switching signals.

F0 action The reproduction sound field correction circuit detects multipath fading and generates control voltages for high-cut and blend operations.The control voltage and control voltage are set to have a rise time constant of several seconds as a long time constant of the control voltage generation circuit. The signal meter voltage input to the generation circuit is smoothed by a low-pass filter with a long time constant, and the voltage is then compared, and the sound field correction circuit is operated based on the comparison result. The voltage smoothed by the LPF is set lower than the output voltage of the control voltage generation circuit,
Using this as a reference voltage, it is compared with the control voltage.

G. EXAMPLES The present invention will be explained in more detail below using examples with reference to the drawings, but these are merely illustrative and various modifications and improvements can be made without going beyond the scope of the present invention. Of course it is possible.

FIG. 1 is a block diagram showing the configuration of a reproduced sound field correction circuit in the event of multipath interference according to the present invention.

When FM/broadcast waves affected by multipath fading are received and the received waves are converted to an intermediate frequency (abbreviated as If in the Imi Sewer Specification) at the front end, the converted frequency is F is similarly affected by multipath fading. In the figure, 1 indicates the 10.7 MHz IF signal input from the mixer output of the front end.

IF the engineering F affected by multipath fading
Amplification and detection (hereinafter referred to as IF&DE)
It is abbreviated as T. ) It is amplified in the circuit section 2 and subjected to FM detection. This FM-detected audio signal component is input to a stereo demodulator 3, separated into L and R signal components of the stereo signal, amplified by audio amplifiers 4 and 5, and output from speakers SPL and SPR. Here, since the sound output from the speakers SPL and SPR is affected by multipath fading, the sound output from the speakers SPL and SPR may generate intense noise. Therefore, the high-cut and blend function circuits included in the stereo demodulation circuit 3 aim to reduce multipath fading noise. This control is performed using the signal meter voltage, which is generated in the rF&DET circuit section 2 and is proportional to the electric field strength. In other words, a negative dip point occurs in the signal meter voltage when multipath fading occurs. Control is performed by detecting this dip point. This is performed by the control voltage generation circuit 6 shown in FIG. Here, as shown in FIG. 2, the control voltage generation circuit 6 detects the dip component included in the S meter voltage via the coupling capacitor C, and determines the signal meter voltage depending on the magnitude of the dip component. lower. In the system according to the invention, this control voltage is
As shown in the figure, the response characteristics are such that the falling time constant t is small and the rising time constant t2 is large (about several seconds).

This control voltage is input to the high-cut and blend control terminals of the stereo demodulator 3 to control the reproduced sound field and improve the S/N ratio by taking into account the reduction of light distortion caused by multipath fading. When multipath fading occurs and this control voltage decreases, the degree of separation deteriorates due to the blending operation, and the position of the sound source moves to the center. Therefore, the operation of returning the position of the sound source to its original position is performed as described below.

The signal meter voltage is input to the LPF7, which is composed of a resistor R and a capacitor C. Then, if the time constant of LPF7 is sufficiently longer than the period of multipath fading, the dip point disappears as shown in Figure 3, and the voltage VO' remains almost constant.
will be maintained. Voltage V passing through this LPF7. ' is inputted to one input of the comparator 8, and the output voltage vo of the control voltage generation circuit 6 is inputted to the other input. Here, the output voltage ``o'' of the LPF 7 is set lower than the output voltage VO of the control voltage generation circuit 6 by the regulator 8. This is because the sound field correction circuit does not operate under multipath fading that is not very severe. In other words,
Vo'< V. The voltage relationship is as follows. Then, the voltage VO' is used as a reference and compared with the voltage VO. and the reference voltage V. When the control voltage VO becomes smaller than ', the comparator outputs a "high level" signal, which is input to the switch changeover control circuit 10. This switch changeover control circuit 10 outputs an output for controlling changeover switches SWI and SW2 of the sound field correction circuit.

That is, when the output from the comparator 8 becomes high level, the changeover switches SWI and SW2 are turned on.

The fact that the output of the comparator becomes high level means that it is basic I! s
Voltage V. ′, the control voltage V. This means that the
This means that the influence of multipath fading is large.

Next, in the sound field correction circuit, a part of the left signal and right signal components are passed through a high-pass filter (hereinafter abbreviated as HPF in this specification) having a cutoff frequency of about 3 kHz.
11 and 12, only the middle and high frequency components are inverted by inverting circuits 13 and 14, respectively, and added to the right signal and left signal components, respectively. By doing this, the reverse phase component of the right signal component is added to the left signal output, and the reverse phase component of the left signal component is added to the right signal output. Due to this anti-phase component, the left sound source moves to the left, and the right sound source moves to the right.

The cutoff frequency of the HPF is 3 kHz because low frequency components have little to do with localization of a sound image.

The changeover switches SWI and SW2 are in the off state when multipath fading is not occurring, and the separated left and right signal components from the stereo demodulator 3 are output from the speakers as they are, and the normal position is maintained. Use as a sound source.

The switches SWI and SW2 are analog switches composed of transistors and the like. By automatically operating such a sound field correction circuit when multipath fading occurs, it is possible to suppress changes in sound image due to high cut and blend operations.

Effects of the H0 Invention When the reproduction sound field is changed by high-cut and blend operations when multipath interference occurs, the sound image constantly moves, making the listener feel uncomfortable. However, as explained above, according to the present invention, if the position of the sound image is about to change, it is returned to its original position, so there is an advantage that a stable reproduction sound field can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a reproduced sound field correction circuit according to the present invention, Fig. 2 is a control voltage waveform diagram in the circuit shown in Fig. 1, and Fig. 3 is a signal meter voltage with a dip point after passing through an LPF. The waveform diagram and FIG. 4 are top views for explaining changes in sound source position during high cut and blend operations due to multipath fading. 1...F signal input from front end mixer output, 2...IF and DET
Circuit, 6... Control voltage generation circuit, 7...
......LPF, 8...Comparator,
9・・・・・・・・・Adjuster, 10・・・・・・・・・
Switch switching control circuit, 11, 12...
...HPF, 13.14...Inverting circuit, S
WI, SW2...Switch, SPRlS
Pt・・・・・・Speaker.

Claims (1)

[Scope of Claims] (a) A control voltage circuit that generates high-cut and blend control voltages for the stereo demodulation circuit based on the signal meter voltage, (b) Low-pass filter means that removes the dip voltage of the signal meter, (c) Sound field correction means that adds an inverse phase component of the middle and high range components of the right signal output to the left signal output, and adds an inverse phase component of the middle and high range components of the left signal output to the right signal output; (d) Switching of the sound field correction means. and (e) comparison means for issuing a control signal to the switching signal generating means by comparing the voltage generated by the control voltage and the means for removing the dip voltage. Playback sound field correction circuit when path interference occurs.