JPH05167366A - In-vehicle sound reproduction device - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize an in-vehicle sound reproducing device capable of solving a lack of bass without deteriorating the SN ratio of the reproduced sound in the high and middle frequencies. [Structure] Low-frequency components of acoustic signals output from the low-pass filters 21 and 22 are added to adders 23 and 24 with the back reflection sound delayed and convoluted by the reflection sound generation unit 4. By reproducing this acoustic signal from the rear speaker, the low frequency component is corrected. The forward reflected sound obtained from the reflected sound generation unit 4 has a flat frequency characteristic. When this signal and the acoustic signal source are added by the adders 7 and 8, a natural reflected sound can be obtained, and the SN ratio in the middle and high frequencies does not deteriorate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle-mounted on-vehicle sound reproducing device having a sound reproduction characteristic corrected.

[0002]

2. Description of the Related Art In recent years, as a car audio system, there has been used a digital signal processor which corrects a sound reproduction characteristic in an amplification circuit section of a sound signal in order to obtain a feeling of presence and a sense of spaciousness in a vehicle. In addition, in order to compensate for the lack of low-frequency reproduction due to the limitation of the diameter of the speaker installed in the vehicle and the lack of back surface capacity, the low-frequency component of the acoustic signal is electrically corrected, and the in-vehicle acoustic reproduction device that enables comfortable music listening is provided. Development is in progress.

An example of a conventional vehicle-mounted sound reproducing device will be described with reference to FIGS. 10 and 11. FIG. 10 is a block diagram showing the configuration of a conventional vehicle-mounted sound reproduction device. In the figure, an acoustic signal source 1 is a signal source for outputting an acoustic signal of a radio or a music reproducing device attached to a vehicle. The low-frequency correction unit 2 is a frequency characteristic correction circuit for emphasizing the low-frequency components of the output signals of the L and R channels of the acoustic signal source 1. FIG. 11A shows the frequency characteristic of the low-frequency correction unit 2. In FIG. 10, the low-frequency correction unit 2 is, for example, 100H.
Frequency components above _Z are allowed to pass, while 100H _Z
The component below is a frequency selective amplifier which increases the gain by 10 dB. The A / D converter 3 converts the analog output of the low-frequency correction unit 2 into a digital signal, and the output is given to the reflected sound generation unit 4. The reflected sound generation unit 4 delays the input signal with a plurality of delay times, amplifies each delayed signal with a different gain, and then mixes the signals by convolution calculation to generate a reflected sound in the front and back. Is.

The two output signals of the reflected sound generator 4 are D / A
It is provided to the converters 5 and 6. The D / A converters 5 and 6 convert the delay-processed digital audio signal into a stereo analog signal. The signals of the two channels of the D / A converter 5 are given to the first adders 7 and 8, respectively. The adders 7 and 8 are circuits that add the undelayed left and right channel acoustic signals output from the low-frequency correction unit 2 and the delayed acoustic signals of the D / A converter 5. The respective outputs of the adders 7 and 8 are given via power amplifiers 9 and 10 to speakers 11 and 12 attached to the front left and right doors of the vehicle, respectively. The signals of the two channels of the D / A converter 6 are given to the speakers 15 and 16 mounted on the left and right of the rear tray of the vehicle via the power amplifiers 13 and 14, respectively.

The operation of the on-vehicle sound reproducing device thus configured will be described. The acoustic signal output from the acoustic signal source 1 is input to the low-frequency correction unit 2, and the low-frequency component is emphasized as shown in FIG. The analog stereo sound signal corrected by the low-frequency correction unit 2 is converted into a digital signal by the A / D converter 3. Here, the level of the output signal of the low-frequency correction unit 2 must not exceed the maximum allowable level of the A / D converter 3. That is, assuming that the +10 dB input acoustic signal output from the low-frequency correction unit 2 is the maximum input level (0 dB) of the A / D converter 3 as shown in FIG.
As shown in the frequency characteristic of (b), the input signal level in the middle and high frequencies is supplied to the A / D converter 3 with a reduction of 10 dB compared with the low frequency range.

Next, the output of the A / D converter 3 is given to the reflected sound generating section 4, and the reflected sound before and after the original sound signal is generated. This reflected sound is generated in order to create a realistic and expansive feeling in the actual sound field inside the vehicle.For people sitting on the seat in front of the vehicle, the reverberation sounds from the front and rear are different. Set to feel the effect. Now, of the reflected sound output from the reflected sound generation unit 4,
The signal reproduced by the front speaker is converted into an analog signal again by the D / A converter 5, and the low-frequency correction unit 2 is added by the adders 7 and 8.
It is added with the acoustic signal output from. This signal is amplified by the power amplifiers 9 and 10, and sound is output from the left and right speakers 11 and 12. This voice is a reflection-free component added with a reflection component that is natural.

On the other hand, the rear reflected sound output from the reflected sound generating section 4 is converted into an analog signal by the D / A converter 6, amplified by the power amplifiers 13 and 14, and then the left and right speakers 15 at the rear of the vehicle. The sound of only the reflection component is output from 16. As described above, in the conventional vehicle-mounted sound reproduction device, the low-frequency component of the input signal is electrically emphasized by the low-frequency correction unit 2, so that both the direct sound and the reflected sound are amplified and the low-frequency range of the reproduced sound in the vehicle is insufficient. Was compensating for.

[0008]

However, in the above-mentioned conventional configuration, since the low frequency component of the signal input to the A / D converter is amplified in advance, the dynamic range of the acoustic signal in the middle and high frequency range is small. Will be things. Therefore, the SN ratio of both the front and back reflected sounds deteriorates in the middle and high frequencies, which hinders comfortable listening to music.

The present invention has been made in view of the above conventional problems, and by eliminating the shortage of low frequency components without deteriorating the SN ratio of the reproduced sound in the middle and high frequencies,
It is an object of the present invention to provide an in-vehicle sound reproduction device that enables more comfortable listening to music.

[0010]

According to the invention of claim 1 of the present application, an acoustic signal source for outputting an acoustic signal, an A / D converter for converting the output of the acoustic source into a digital signal, and an A / D converter. Of the output signal of D.A., which produces forward reflected sound and backward reflected sound by delay processing and convolution processing, and D / A which converts the forward and backward digital signals output from the reflected sound generation section into analog signals. A converter, a first adder for adding the forward reflected sound output from the D / A converter and the left and right acoustic signals of the acoustic signal source, and a plurality of low frequency components for extracting the low-frequency component of the acoustic signal of the acoustic signal source. Low-pass filter and the other D
And a second adder that adds the back reflected sound output from the / A converter and the output signal of the low-pass filter.

According to the invention of claim 2 of the present application, the low-pass filter is characterized in that the cut-off frequency is set to be equal to or lower than the resonance frequency of the passenger compartment in which the acoustic signal source is mounted.

The invention according to claim 3 of the present application is characterized in that a band cutoff filter for attenuating the resonance frequency band of the passenger compartment is connected in series to the low-pass filter.

The invention according to claim 4 of the present application has a noise detecting section for detecting a noise level in the vehicle, and the low-pass filter changes the output level based on the output of the noise detecting section. To do.

[0014]

According to the invention of claim 1 of the present application having such a feature, the output of the acoustic signal source is digitized by the A / D converter, and this signal is given to the reflected sound generation unit to perform delay processing and convolution. Processing is performed to generate a front reflected sound and a back reflected sound. Then, the back reflected sound and the direct sound in which the low-frequency component is emphasized by the low-pass filter are added by the second adder. A /
Since the D converter digitally processes the acoustic signal at the same signal level in the entire frequency band, the SN ratio of the generated front reflected sound and rear reflected sound does not deteriorate in the middle and high frequencies.

According to the invention of claim 2 of the present application, claim 1
In addition to the above effect, the cutoff frequency of the low-pass filter is set to the resonance frequency of the vehicle interior or lower to lower the amplification of the acoustic signal in the resonance frequency band of the vehicle, and the reproduction sound in the resonance frequency band at the time of low frequency amplification. Prevent the level from rising.

Further, according to the invention of claim 3 of the present application, in addition to the operation of claim 1, by making the center frequency of the band cutoff filter equal to the resonance frequency of the vehicle, the low pass filter from the low pass filter in the resonance frequency band of the vehicle is provided. Attenuates the output signal to prevent an increase in the reproduced sound level in the resonance frequency band during low-frequency amplification.

According to the invention of claim 4 of the present application, claim 1
In addition to the above effect, the output signal level of the low-pass filter is increased as the noise level detected by the noise detection unit increases, so that the acoustic effect in the vehicle is not deteriorated.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an in-vehicle sound reproduction device according to the first embodiment of the present invention. In the figure, an acoustic signal source 1, an A / D converter 3, a reflected sound generating unit 4, D / A converters 5, 6, adders 7, 8, power amplifiers 9, 10, 13, 14, a speaker 11, 12, 15, 1
Since 6 is the same as the conventional example, the description thereof is omitted.
In the vehicle-mounted sound reproduction device of this embodiment, unlike the conventional example, the stereo sound signal of the sound signal source 1 is added to the adders 7, 8 and the A / D.
It is given directly to the converter 3, and at the same time, given to the low-pass filters (LPF) 21 and 22.

The LPFs 21 and 22 are the same filters that pass acoustic signals of low frequency, and a concrete circuit configuration example thereof is shown in FIG. In this figure, the acoustic signal source 1
Is applied to the non-inverting input section of the operational amplifier A1 via the resistors R1 and R2 connected in series. A feedback capacitor C2 is connected between the output terminal and the connection point of the resistors R1 and R2, and the resistor R is connected between the output terminal and the ground.
4, R3 are connected in series. The non-inverting input section of the operational amplifier A1 is grounded via the capacitor C1, and the inverting input section is directly connected to the connection point of the resistors R3 and R4. The output of each operational amplifier A1 of LPF21 and LPF22 is
It is given to the second adders 23 and 24 shown in FIG. 1, respectively.
Figure 2 (b) is a frequency characteristic of the LPF 21, LPF 22, and set the cut-off frequency f _C1 of the value of around for example 100 ~200H _Z.

Assuming that the cutoff frequency of the low-pass filter is f _C , the amplification factor is G _C , and Q is f _C1 , then f _C , G
_C, Q _C is expressed by the following equation.

[Equation 1] The a and b used here are expressed by the following equations.

[Equation 2] In this embodiment, the cutoff frequency f _C1 is set to be _{equal to} or higher than the resonance frequency f _Q of the passenger compartment.

The adder 23 adds the left acoustic signal of the D / A converter 6 and the output of the LPF 21, and the adder 24 adds the D / A.
The right acoustic signal of the converter 6 and the output of the LPF 22 are added. The outputs of the adders 23 and 24 are given to the speakers 15 and 16 via the power amplifiers 13 and 14 as in FIG. On the other hand, the outputs of the adders 7 and 8 are given to the speakers 11 and 12 via the power amplifiers 9 and 10.

The operation of the vehicle-mounted sound reproducing apparatus of the first embodiment constructed as described above will be described. The analog audio signal of the audio signal source 1 is digitally converted by the A / D converter 3. The frequency characteristic of this acoustic signal is not corrected, and the maximum allowable signal level is the same in all frequency bands.
Therefore, the A / D converter 3 can process the signal at the same level in the entire frequency band, and the level in the middle and high frequencies does not decrease. Then, this output is given to the reflected sound generation unit 4, and the reflected sound is generated by performing a convolution operation by performing delay processing as in the conventional example. Next, this reflected sound is added to the direct sound from the LPFs 21 and 22 by the adders 23 and 24, and the sound is reproduced from the rear speakers 15 and 16 in a state in which a sense of presence and a sense of spaciousness are added.

On the other hand, the forward reflected sound output from the reflected sound generating unit 4 is set to have a delay time shorter than that of the rear reflected sound, and the signal whose frequency characteristic is not corrected and this reflected sound are added by the adders 7 and 8. The added sounds are reproduced from the front speakers 11 and 12 to give a natural sound.

As described above, according to this embodiment, since the maximum allowable signal level of the input of the A / D converter 3 is the same in all frequency bands, the signal is processed in a wide dynamic range here. Therefore, it is possible to efficiently amplify the low-frequency component, which tends to be insufficient in the vehicle, without deteriorating the SN ratio in the middle and high frequencies of the front reflected sound and the rear reflected sound. In particular, since the front speakers 11 and 12 of the vehicle are arranged at the door portion, the back surface capacity is small and it is difficult to reproduce the sound of the low frequency component. However, bass sounds generally do not have a feeling of localization, and even if bass sounds are reproduced only from the rear, there is little discomfort and there is no problem. That is,
As long as the bass is sufficiently reproduced from the rear speakers 15 and 16 arranged on the rear tray, the lack of bass is not felt even if the bass is not reproduced from the front speaker. still,
Here, the reflected sound is emphasized in the low frequency range and is not amplified, but in general, the signal level of the reflected sound is lower than the direct sound and the direct sound is dominant. Is obtained.

Next, a second embodiment of the present invention will be described. The configuration of the on-vehicle sound reproducing device of this embodiment is the same as that of the first embodiment, but the cutoff frequencies f _C2 of the LPFs 21 and 22 are set to be equal to or lower than the resonance frequency f _{Q of the} vehicle. Figure 3
Is a frequency characteristic of the LPFs 21 and 22, and FIG. 4 is a frequency characteristic diagram showing a reproduced sound level inside the vehicle. Curve S in FIG.
Reference _numeral 1 indicates the reproduced sound level inside the vehicle in the first embodiment (f _Q <f _C1 ), and curve S2 indicates the reproduced sound level in the passenger compartment in this embodiment. A common peak existing at the same low frequency of the curves S1 and S2 is a resonance frequency due to a resonance phenomenon according to the vehicle interior length and volume, and is usually 1 for passenger cars.
Occurs in the frequency band of about 00Hz to 300Hz.

As shown in FIG. 4, the reproduced sound in the passenger compartment has a low-amplified reproduced sound level further increased due to the resonance of the vehicle in the curve S1, and an uncomfortable muffled sound is generated. However, in this embodiment, the cutoff frequency f _C2 is set to a value equal to or lower than the vehicle resonance frequency f _Q. Therefore, the reproduction frequency characteristic changes from the curve S1 to the state shown in the curve S2,
The muffled sound in the car is kept low.

As described above, according to the present embodiment, as in the first embodiment, the SNs in the middle and high frequencies of the front reflected sound and the rear reflected sound.
It is possible to amplify the low frequency component lacking in the passenger compartment without deteriorating the ratio. Also low-pass filter 2
By setting the cutoff frequencies of 1 and 22 to be equal to or lower than the resonance frequency of the passenger compartment, the amplification degree of the output signals of the low-pass filters 21 and 22 in the resonance frequency band is lowered, and the reproduced sound level in the resonance frequency band during low-frequency amplification It is possible to prevent the muffled sound from being generated due to the rise of the.

Next, a third embodiment of the present invention will be described. FIG. 5 is a block diagram showing the configuration of an on-vehicle sound reproduction device according to the third embodiment of the present invention. In the figure, an acoustic signal source 1, an A / D converter 3, a reflected sound generator 4, D / A converters 5, 6, adders 7, 8, LPFs 21, 22 and power amplifiers 9, 10, 13, 14 , Speakers 11, 12, 1
Since the components 5 and 16 are the same as those in the first embodiment, the description thereof will be omitted. Unlike the first embodiment, the on-vehicle sound reproducing apparatus of this embodiment has the same band cutoff filter (BE) between the LPFs 21 and 22 and the adders 23 and 24, respectively.
F) 31 and 32 are provided.

The BEFs 31 and 32 are band elimination filters that cut off only the components near a specific frequency, and a concrete configuration example thereof is shown in FIG. As shown in the figure, the BEF filters 31 and 32 are active band-elimination filters in which a T-notch filter and an operational amplifier A2 are combined, and the respective resistance values and capacitances are as shown. Here, these BEF filters 31,
When the center frequency of 32 is f _O and the amplification degrees G _O and Q of the operational amplifier A2 are Q _O , f _O , G _O and Q _O are respectively given by the following equations.

[Equation 3] The multipliers d and e used here are expressed by the following equations.

[Equation 4]

Here, the center frequency f _O of the BEF filters 31 and 32 is set equal to the resonance frequency f _Q of the passenger compartment. Here, the total characteristics of the LPF 21 and the BEF 31 are shown in FIG. f _C is the cutoff frequency of the low pass filter LPF 21, and f _O is the center frequency of the BEF filter 31. The outputs of the BEFs 31 and 32 are given to the adders 23 and 24 shown in FIG. 5, respectively.

With respect to the on-vehicle sound reproducing apparatus of the present embodiment having the above-mentioned structure, the operation of the parts different from those of the first and second embodiments will be described. FIG. 7B shows the frequency characteristic of the reproduced sound level in the passenger compartment. In this figure, BEF31,3
While the reproduced sound level in the passenger compartment when not using No. 2 is in the state shown in the curve S3, when the resonance frequency f _{Q of the} vehicle and the cutoff frequency f _O are set to be the same, the state is shown in the curve S4. That is, conventionally, the reproduced sound in the passenger compartment was raised in the resonance frequency band of the passenger compartment due to the resonance and low-frequency amplification of the passenger compartment, and an unpleasant muffled sound was generated. Generation of muffled sound is suppressed.

As described above, according to this embodiment, as in the first and second embodiments, the SN ratio in the mid-high range of the front reflected sound and the rear reflected sound is not deteriorated and the vehicle interior tends to be insufficient. It is possible to sufficiently reproduce the sound of the low frequency component. Further, it is possible to prevent the muffled sound from being generated due to the increase in the reproduced sound level in the resonance frequency band at the time of low frequency amplification.

Next, a fourth embodiment of the present invention will be described. FIG. 8 is a block diagram showing the configuration of an on-vehicle sound reproduction device according to the fourth embodiment of the present invention. In the figure, an acoustic signal source 1, an A / D converter 3, a reflected sound generator 4, D / A converters 5, 6, adders 7, 8, power amplifiers 9, 10, 1
3 and 14, and the speakers 11, 12, 15, and 16 are provided respectively, which is the same as in the first embodiment.
Omit it. The on-vehicle sound reproducing device of this embodiment has a variable resistor for changing the gains of the low-pass filters 41 and 42. Further, a control unit 44 for controlling the amplification factor based on the output level of the noise detection unit 43 is provided. The noise detection unit 43 in the figure is a sensor that detects the running noise of the automobile, and its output is given to the control unit 44.
The control unit 44 gives a control signal to the LPFs 41 and 42 according to the signal level from the noise detection unit 44, and changes the amplification factor thereof.

With respect to the on-vehicle sound reproducing apparatus of this embodiment having the above-mentioned structure, only the operation different from that of the first embodiment will be described. FIG. 9 is a frequency characteristic diagram of the reproduced sound level and the noise level in the vehicle. In the figure, curve N0 is the noise level when the vehicle is stopped, and N1 is the noise level when the vehicle is running. Curves S5 and S6 represent reproduced sound levels when the vehicle is at a low stop and when the vehicle is running. By the way, the noise level during running greatly increases compared to the noise level when stopped. In particular, the low-frequency component level of the noise level during running is significantly higher than that during stopping.

The control unit 44 sends control signals corresponding to the noise level in the vehicle detected by the noise detection unit 43 to the LPFs 41 and 42.
To increase the amplification factor as the noise level increases. Therefore, when the vehicle travels and the noise level in the vehicle increases, correction is automatically performed so that the low frequency component of the acoustic signal is emphasized. In this way, the low-frequency amplification factor is varied during running, and the masking of reproduced sound due to running noise is improved. In this way, similar to the first embodiment, it is possible to emphasize low-frequency components that tend to be insufficient in the vehicle, without deteriorating the SN ratio of the middle and high frequencies of the front reflected sound and the rear reflected sound.

[0036]

As described in detail above, according to the invention of claim 1 of the present application, it is possible to prevent deterioration of the SN ratio in the mid-high range of the front reflected sound and the rear reflected sound, and further it is insufficient in the vehicle. The effect of sufficiently amplifying the low-frequency component sound that tends to be obtained is obtained, and its practical value is great.

Further, according to the second and third aspects of the present invention, it is possible to amplify the low frequency component lacking in the vehicle without deteriorating the SN ratio of the middle and high frequencies of the front reflected sound and the rear reflected sound. In addition to this, it is possible to obtain the effect of preventing muffled sound from being generated due to an increase in the reproduced sound level in the resonance frequency band of the vehicle during low-frequency amplification.

Further, according to the invention of claim 4, the low frequency component lacking in the vehicle can be amplified without deteriorating the SN ratio of the middle and high frequencies of the front reflected sound and the rear reflected sound. Therefore, it is possible to prevent the masking of the low frequency component of the reproduced sound due to the running noise of the automobile.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an in-vehicle sound reproduction device according to a first embodiment of the present invention.

FIG. 2A is a circuit diagram of a low-pass filter used in the vehicle-mounted sound reproduction device of the first embodiment, and FIG. 2B is a frequency characteristic diagram of the low-pass filter.

FIG. 3 is a frequency characteristic diagram of reproduced sound in the second embodiment of the present invention.

FIG. 4 is a frequency characteristic diagram of a reproduction level inside a vehicle in the second embodiment.

FIG. 5 is a block diagram showing a configuration of an on-vehicle sound reproduction device in a third embodiment of the invention.

FIG. 6 is a circuit diagram of a band stop filter used in the third embodiment.

FIG. 7A is a frequency characteristic diagram of a band stop filter of the third embodiment, and FIG. 7B is a frequency characteristic diagram of reproduced sound.

FIG. 8 is a block diagram showing a configuration of an on-vehicle sound reproduction device in a fourth embodiment of the invention.

FIG. 9 is a frequency characteristic diagram of reproduced sound in the fourth embodiment.

FIG. 10 is a block diagram showing a configuration of a conventional vehicle-mounted sound reproduction device.

FIG. 11 is an explanatory diagram of frequency correction characteristics in a conventional vehicle-mounted sound reproduction device.

[Explanation of symbols]

 1 Acoustic Signal Source 3 A / D Converter 4 Reflected Sound Generator 5, 6 D / A Converter 7, 8, 23, 24 Adder 9, 10, 13, 14 Power Amplifier 11, 12, 15, 16 Speaker 21 , 22, 41, 42 LPF 31, 32 BEF 43 Noise detection unit 44 Control unit

Claims (4)

[Claims] 1. An acoustic signal source for outputting an acoustic signal, an A / D converter for converting an output of the acoustic source into a digital signal, and an output signal of the A / D converter by delay processing and convolution processing. A reflected sound generation unit that generates a front reflected sound and a rear reflected sound, a D / A converter that converts front and rear digital signals output from the reflected sound generation unit into an analog signal, and the D / A converter A first adder for adding the front reflected sound output from the acoustic signal source and the left and right acoustic signals of the acoustic signal source; a plurality of low-pass filters for extracting low-frequency components of the acoustic signal of the acoustic signal source; An in-vehicle sound reproduction device comprising: a back adder output from a D / A converter and a second adder that adds the output signal of the low-pass filter. 2. The on-vehicle sound reproduction device according to claim 1, wherein the low-pass filter has a cutoff frequency set to be equal to or lower than a resonance frequency of a vehicle compartment in which the acoustic signal source is mounted. 3. The on-vehicle sound reproducing device according to claim 2, wherein a band cutoff filter for attenuating a resonance frequency band of the vehicle compartment is connected in series to the low-pass filter. 4. A noise detecting section for detecting a noise level in the vehicle, wherein the low-pass filter changes its output level based on an output of the noise detecting section. The in-vehicle sound reproduction device described.