JP2001333491A - Acoustic reproduction system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an acoustic reproduction system that reduces noise when noise with a very high level is generated or a reproduction level of an audio signal is very high, and does not generate an abnormal sound with high distortion from a speaker giving an adverse effect on the reproduction of the audio signal. SOLUTION: This acoustic reproduction system is provided with an interference signal generating means 106 and a limiting amplifier means 105. A 1st mixer 104 provided in a pre-stage of the limiting amplifier means 105 receives an output signal from an audio compensation signal generating means 103.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound reproduction system capable of reducing noise and reproducing music.

[0002]

2. Description of the Related Art A sound reproducing system as shown in FIG. 6 has been proposed as a method of reproducing music while actively reducing road noise of a vehicle.

In FIG. 6, reference numeral 501 denotes a microphone.
A sound wave including a reproduced sound and a noise of the audio signal is detected near the driver's seat in the passenger compartment 502, and an interference wave signal having a phase opposite to that of the sound wave is detected from the signal by a filter 503 as an interference wave signal generation unit. create. This interference wave signal and an audio signal from a radio tuner, a tape deck, or the like are added by a first mixer 504, and then power-amplified by a power amplifying unit 505 and output from a speaker 506 as a sound wave.
2 radiated. This reduces noise, but also changes the reproduced sound of the audio signal. Therefore, an audio compensation signal is created from the audio signal by the audio compensation signal creation means 507,
The audio compensation signal and the output signal of the first mixer 504 are compensated by being added by the second mixer 508,
The playback of the audio signal is not affected. The audio compensation signal is created from the audio signal so that it has the same amplitude and opposite phase as the signal fed back by the microphone 501 when the audio signal is reproduced. The audio compensation signal creating means 507 is composed of a phase and amplitude adjustment circuit and a delay circuit.

[0004]

However, an example of the measured spectrum of the road noise when the vehicle is traveling on a general road is shown in FIG. 7, and the worst influence on the audibility is around 40 Hz. The peak of the noise. This frequency range creates a very uncomfortable feeling of pressure and muffledness. However, in the case of the sound reproduction system as shown in FIG. 6, a great effect on audibility can be obtained by reducing the peak of the noise around 40 Hz. 30Hz shown in 7
The following signal for canceling a very high noise level signal is applied to the speaker 506. Speaker 506
Since an electrodynamic loudspeaker is generally used, when an excessively low frequency component is input, the amplitude becomes extremely large, a loud distortion sound is generated, and a practical problem occurs.
Further, when traveling on a step or a seam of a road, noise having a larger amplitude is generated, and it is difficult to apply the sound reproducing system as shown in FIG. 6 to an actual vehicle. In addition, even when the reproduction level of the audio signal is increased, in this acoustic reproduction system, an abnormal sound with a large distortion is generated from the speaker 506, and the reproduction of a good audio signal is hindered.

According to the present invention, even when a very loud noise is generated, it is possible to reproduce the audio signal while always maintaining the compensation level of the audio signal at an appropriate level without generating an abnormal sound with a large distortion from a speaker. In addition, when the reproduction level of the audio signal becomes extremely large, the noise reduction capability as well as the audio signal compensation capability are automatically reduced, and the distortion from the loudspeaker adversely affects the audio signal reproduction. It is an object to realize a sound reproduction system that does not generate sound.

[0006]

In order to solve the above-mentioned problems, a sound reproducing system according to the present invention comprises a transducer for detecting a reproduced sound of an audio signal and noise or vibration having a high correlation with the noise, and a reproducing apparatus for reproducing the audio signal. Audio compensation signal creating means for creating, from the audio signal, a compensation signal for canceling the audio signal component fed back from the transducer, and a first signal for adding the output signal of the transducer and the output signal of the audio compensation signal creating means. And the output signal of the first mixer is input, and when the amplitude of the input signal is equal to or smaller than a predetermined output amplitude, the output signal of the first mixer is amplified at a constant amplification degree. When the amplitude of the input signal exceeds the predetermined output amplitude. Includes limiting amplifier means for said output amplitude to a predetermined variable and outputs an amplification degree according to the magnitude of the output signal of the first mixer so as to be substantially an upper limit,
Interference wave signal creation means for creating an interference wave signal for reducing the noise by interfering with the noise from the output signal of the limiting amplification means, and adding the output signal of the interference wave signal creation means and the audio signal A second mixer, power amplifying means to which an output signal of the second mixer is input,
An electroacoustic conversion unit that receives an output signal of the power amplification unit and emits a sound wave. With this configuration, even when a very loud noise is generated, the audio signal can be reproduced with the compensation level of the audio signal always kept at an appropriate level without generating an abnormal sound with large distortion from the speaker. When the playback level of an audio signal becomes extremely large, the noise reduction capability and the audio signal compensation capability are automatically reduced, and abnormal sound with large distortion from the speaker that adversely affects the audio signal playback is generated. It is possible to realize a sound reproduction system that does not cause the sound reproduction.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, a transducer for detecting a reproduced sound of an audio signal and a noise or a vibration highly correlated with the noise, and a feedback from the transducer by reproducing the audio signal. Audio compensation signal creating means for creating a compensation signal for canceling the audio signal component from the audio signal, a first mixer for adding an output signal of the transducer and an output signal of the audio compensation signal creating means, and When the output signal of the first mixer is input and the amplitude of the input signal is equal to or smaller than a predetermined output amplitude, the output signal of the first mixer is amplified and output at a constant amplification degree, and When the amplitude of the input signal exceeds the predetermined output amplitude, the predetermined output amplitude is used. Amplifying means for varying the degree of amplification in accordance with the magnitude of the output signal of the first mixer so that the noise level is substantially equal to the upper limit, and the noise by interfering with the noise from the output signal of the limiting amplifying means. Signal generating means for generating an interference signal for reducing noise, a second mixer for adding an output signal of the interference signal generating means and the audio signal, and an output signal of the second mixer being input. Power amplification means, and an electroacoustic conversion means for receiving an output signal of the power amplification means and emitting a sound wave, so that even when extremely loud noise is generated, abnormal sound with large distortion is generated from the speaker. The audio signal can be reproduced with the compensation level of the audio signal always kept at an appropriate level without occurrence, and when the reproduction level of the audio signal becomes extremely large. Also it has an effect of not automatically compensated ability noise reduction capability only if the audio signal is also reduced to generate a large abnormal noise distortion from the speaker adversely affect the reproduction of the audio signal.

According to a second aspect of the present invention, there is provided a transducer for detecting a reproduced sound of an audio signal and noise or vibration having a high correlation with the noise, and for canceling an audio signal component fed back from the transducer by reproducing the audio signal. Audio compensation signal creation means for creating the compensation signal from the audio signal; and an interference wave signal creation means for receiving an output signal of the transducer and creating an interference wave signal for reducing the noise by interfering with the noise. A first mixer that adds an output signal of the interference wave signal generation unit and an output signal of the audio compensation signal generation unit, and an output signal of the first mixer that is input, and the amplitude of the input signal is When the output amplitude is equal to or less than a predetermined output amplitude, the output signal of the first mixer is changed to a fixed value. When the amplitude of the input signal exceeds the predetermined output amplitude, the output signal of the first mixer is output so that the predetermined output amplitude becomes substantially the upper limit. Amplifying means for varying the degree of amplification according to the magnitude of the signal, a second mixer for adding the output signal of the limiting amplifying means and the audio signal, and an output signal of the second mixer. Power amplifying means and an electroacoustic converting means for receiving an output signal of the power amplifying means and emitting a sound wave, so that even when a very loud noise is generated, an abnormal sound with a large distortion is generated from the speaker. The audio signal can be played back with the compensation level of the audio signal always kept at an appropriate level without the need to perform the automatic operation even when the playback level of the audio signal becomes extremely large. Has the effect of compensating capability of the noise reduction capability only if the audio signal is also reduced, it does not generate a large abnormal noise distortion from the speaker adversely affect the reproduction of the audio signal.

An embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is an explanatory diagram for explaining an embodiment of a sound reproducing system according to the present invention. In FIG. 1, reference numeral 101 denotes a microphone as a transducer, which is disposed near a driver's seat in a vehicle interior 102, detects noise and reproduced sound of an audio signal from a radio tuner, a cassette deck, or the like, and converts it into an electric signal. Reference numeral 103 denotes an audio compensation signal creating unit that creates an audio compensation signal from the audio signal. 104 is the microphone 1
01 is a first mixer for adding the output signal of the audio compensation signal generation unit 103 to the output signal of the audio compensation signal generation unit 103. 105
If the amplitude of the output signal is below a predetermined threshold,
When the amplitude of the output signal exceeds the threshold value, the input signal is amplified at a certain amplification degree, and when the amplitude of the output signal exceeds the threshold value, the threshold value becomes substantially equal to the upper limit value of the amplitude of the output signal. This is limiting amplification means for varying the amplification degree of the input signal and outputting the result. Reference numeral 106 denotes an interference wave signal generation unit that generates an interference wave signal that reduces noise by causing interference with noise.
Reference numeral 107 denotes a second mixer that adds the output signal of the interference wave signal generation unit 106 and the audio signal. 108 is the second
Power amplifying means for amplifying the output signal of the mixer 107 of FIG. Reference numeral 109 denotes a speaker as an electroacoustic conversion unit that receives an output signal of the power amplification unit 108 and emits a sound wave into the vehicle interior 102.

The above-mentioned audio compensation signal creating means 103
When the audio signal is reproduced, the microphone 10
1 and a signal having the same amplitude and opposite phase as the signal generated in the audio signal 1. Also, the microphone 101, the first mixer 104, the limiting amplifier 10
5, interference wave signal creating means 106, second mixer 107,
A path leading to the power amplifying means 108 and the speaker 109 forms a closed loop via the vehicle interior 102. The loop transfer function of this closed loop is F (s), and the microphone 101
Let Vn be the original noise at the position, and Vn 'the noise at the position of the microphone 101 when the closed loop is operated.

[0012]

(Equation 1)

When F (s) is represented by amplitude and phase, noise is reduced in the frequency range where the phase is around 180 °.

FIG. 2 shows the loop transfer function F (s) when the sound reproduction system shown in FIG.
FIG. 4 is a characteristic diagram represented by a phase. In FIG. 2, it can be seen that the noise in the frequency band near 40 Hz is reduced because the amplitude characteristic peaks near 40 Hz and the phase is near 180 °. The interference wave signal creation means 106 determines the loop transfer function F
(S) is responsible for adjusting the phase and amplitude so as to satisfy the above conditions.

FIG. 3 is a block diagram showing a specific configuration example of the limiting amplification means 105 shown in FIG. Reference numeral 301 denotes an operational amplifier, and reference numeral 302 denotes a transconductance amplifier having an output of the operational amplifier 301 as an input and an output connected to a minus input of the operational amplifier 301. The transconductance amplifier 302 has a configuration in which conductance can be varied by a current flowing through an external current terminal 303. The conductance increases when the current is large, and decreases when the current is small. Reference numeral 304 denotes a window comparator, which is connected to the output of the operational amplifier 301. The window comparator 304 is connected to a positive power supply as an output in a section where the absolute value of the output of the operational amplifier 301 exceeds a certain threshold, and has an operation of opening when the absolute value of the output is equal to or less than the threshold. Reference numeral 305 denotes a time constant setting circuit composed of a capacitor and a resistor, which is connected to the output of the window comparator 304. A constant current source 306 generates a current proportional to the output voltage of the time constant setting circuit 305. The output current of the constant current source 306 is
02 is supplied to the external current terminal 303. Reference numeral 307 denotes a resistor connecting the input to the negative input of the operational amplifier 301, and reference numeral 308 denotes a resistor connecting the output of the operational amplifier 301 to the negative input.

The operation of the limiting amplifier 105 will be described below. When the output voltage of the time constant setting circuit 305 is zero, the output current from the constant current source 306 becomes zero. At this time, the conductance of the transconductance amplifier 302 is zero, and the amplification of the limiting amplifier 105 is a constant value determined by the resistor 308 / the resistor 307. On the other hand, when the output of the operational amplifier 301 exceeds the threshold value of the window comparator 304, the time constant setting circuit 305 is connected to a positive power supply, and an output voltage is generated in the time constant setting circuit 305. Output current, the conductance of the transconductance amplifier 302 increases, and equivalently, the operational amplifier 301
Is connected between the output of the operational amplifier 301 and the negative input of the operational amplifier 301, and the amplification degree of the limiting amplifying means 105 decreases from the resistance 308 / resistance 307. When there is a continuous large input, the amplification degree is automatically adjusted so that the output of the operational amplifier 301 slightly exceeds the threshold value of the window comparator 304. That is, the amplification of the operational amplifier 301 changes according to the input signal level so that the output of the operational amplifier 301 becomes substantially equal to the threshold value of the window comparator 304. By using the limiting amplification means 105 in this way, even if there is a strong noise input of 30 Hz or less in the actually measured road noise spectrum shown in FIG. 4, the generation of unnecessary abnormal sounds from the speaker 109 can be prevented.

On the other hand, when an audio signal from a radio tuner or a cassette deck is reproduced, the reproduced sound of the audio signal in the absence of the closed loop is changed by the same mechanism as the above-described noise reduction. Therefore,
In order to prevent a change in the reproduced sound of the audio signal, an audio compensation signal is created by the audio compensation signal creation means 103 and input to the first mixer 104. FIG.
FIG. 2 is a block diagram showing a specific configuration example of an audio compensation signal creating unit 103 shown in FIG. The audio compensation signal creating means 103 is provided with the limiting amplification means 10 shown in FIG.
5. From the interference wave signal creation means 106 to the second mixer 107
A gain adjustment circuit 401, a delay circuit 402, and a frequency characteristic adjustment so that when an audio signal is reproduced in a state where a signal flow to the microphone 101 is interrupted, a signal having substantially the same amplitude and opposite phase as a signal generated in the microphone 101 can be created. It is composed of a circuit 403. As described above, the audio compensation signal is supplied to the first mixer 1
In addition to the function of the limiting amplifier 105, the limiting amplifying means 105 not only functions as a function of substantially reducing the amplification factor when the input noise is large, but also when the reproduced sound of the audio signal is loud. It functions to a lesser degree and the audio compensation level also changes substantially following. As a result, it is possible to reproduce an excellent audio signal without generating an abnormal sound with large distortion from the speaker 109.

In this embodiment, the audio compensation signal generating means is provided in the first stage before the limiting amplifying means.
In addition to the mixer described above, the configuration in which the interference wave signal creating means is provided after the limiting amplification means has been described, but the output signal of the microphone as a transducer is input to the interference wave signal creating means, and the interference wave signal creating means is arranged after the interference wave signal creating means. The first mixer, the limiting amplifier, and the second mixer may be sequentially provided, and the output signal of the audio compensation signal creating unit may be added to the first mixer. That is, the core of the technical idea of the present invention is to provide an interference wave signal generating means and a limiting amplifier in a sound reproducing system, and to input an output signal of the audio compensating signal generating means to a mixer provided in a stage preceding the limiting amplifier. It is in.

In this embodiment, the microphone has been described as a transducer.
In addition, various transducers can be used. Further, it is possible to detect not only the noise directly from the microphone but also vibration having a high correlation with the noise.

In this embodiment, the description has been made using the electroacoustic conversion means and the speaker, but the present invention is not necessarily limited to this.

[0021]

As described above, according to the present invention, a transducer for detecting a reproduced sound of an audio signal and noise or vibration having a high correlation with the noise, and an audio signal component fed back from the transducer by reproducing the audio signal Audio compensation signal creating means for creating a compensation signal for canceling the audio signal from the audio signal, a first mixer for adding an output signal of the transducer and an output signal of the audio compensation signal creating means, When an output signal is input and the amplitude of the input signal is equal to or less than a predetermined output amplitude, the output signal of the first mixer is amplified and output at a fixed amplification degree, and the input signal is output. Is larger than the predetermined output amplitude, the predetermined output amplitude is substantially equal to the upper limit. Limiting amplification means for varying and outputting an amplification degree according to the magnitude of the output signal of the first mixer, and reducing the noise by interfering with the noise from the output signal of the limitation amplification means. Signal generating means for generating the interference wave signal, a second mixer for adding the output signal of the interference wave signal generating means and the audio signal, and a power amplifier to which the output signal of the second mixer is inputted Means, an output signal of the power amplifying means is input, and an electro-acoustic converting means for radiating sound waves, so that even if extremely loud noise is generated, an abnormal sound with large distortion is not generated from the speaker. The audio signal can be played with the compensation level of the audio signal always kept at an appropriate level, and automatically when the playback level of the audio signal becomes extremely large. Compensation capability of the noise reduction capability only if the audio signal is also reduced, it is possible to realize a sound reproduction system that does not generate a large abnormal noise distortion from the speaker adversely affect the reproduction of the audio signal.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an embodiment of a sound reproduction system according to the present invention.

FIG. 2 is a characteristic diagram of a loop transfer function when the system is mounted on a vehicle.

FIG. 3 is a block diagram showing a specific configuration example of a limiting amplification unit of the system.

FIG. 4 is a measured road noise spectrum diagram.

FIG. 5 is a block diagram showing a specific configuration example of an audio compensation signal generation unit according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram for explaining a conventional sound reproduction system.

FIG. 7 is a road noise spectrum diagram when driving on a general road.

[Explanation of symbols]

 Reference Signs List 101 microphone 102 cabin 103 audio compensation signal generation means 104 first mixer 105 limiting amplification means 106 interference wave signal generation means 107 second mixer 108 power amplification means 109 speaker 301 operational amplifier 302 transconductance amplifier 303 external current terminal 304 window comparator 305 Time constant setting circuit 306 Constant current source 401 Gain adjustment circuit 402 Delay circuit 403 Frequency characteristic adjustment circuit 501 Microphone 502 Cab 503 Filter 504 First mixer 505 Power amplifier 506 Speaker 507 Audio compensation signal generator 508 Second mixer

Claims (2)

[Claims] 1. A transducer for detecting a reproduced sound of an audio signal and noise or vibration having a high correlation with the noise,
Audio compensation signal creating means for creating, from the audio signal, a compensation signal for canceling an audio signal component fed back from the transducer by reproduction of the audio signal; an output signal of the transducer and an output signal of the audio compensation signal creating means And an output signal of the first mixer, and when the amplitude of the input signal is equal to or smaller than a predetermined output amplitude, the output signal of the first mixer is fixed. When the amplitude of the input signal exceeds the predetermined output amplitude, the first mixer is controlled so that the predetermined output amplitude is substantially equal to the upper limit. Limiting amplifying means for varying and outputting the degree of amplification in accordance with the magnitude of the output signal; and And interference signal producing means for producing an interference wave signal for reducing the noise by interfering with the sound,
A second mixer that adds the output signal of the interference wave signal creating unit and the audio signal, a power amplifying unit that receives an output signal of the second mixer, and an output signal of the power amplifying unit, An acoustic reproduction system comprising: an electroacoustic conversion unit that emits a sound wave. 2. A transducer for detecting a reproduced sound of an audio signal and noise or vibration having a high correlation with the noise,
Audio compensation signal creation means for creating a compensation signal from the audio signal for compensating the audio signal component fed back from the transducer by reproduction of the audio signal, and an output signal of the transducer is input and interferes with the noise An interference wave signal creating unit that creates an interference wave signal for reducing the noise; a first mixer that adds an output signal of the interference wave signal creating unit and an output signal of the audio compensation signal creating unit; When the output signal of the first mixer is input and the amplitude of the input signal is equal to or smaller than a predetermined output amplitude, the output signal of the first mixer is amplified and output at a constant amplification degree, and When the amplitude of the input signal exceeds the predetermined output amplitude, the predetermined output amplitude is substantially Limiting amplifying means for varying the degree of amplification according to the magnitude of the output signal of the first mixer so as to limit the output, and a second mixer for adding the output signal of the limiting amplifying means and the audio signal And a power amplifying unit to which an output signal of the second mixer is input, and an electroacoustic conversion unit to which an output signal of the power amplifying unit is input and emits a sound wave.