JPH11275682A - Sound reproducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the stable feedback and to secure the feedback effects in a wide band by correcting the output side of a sensor, which detects the reproduced signals at a correction part and connecting the corrected output side to one of both input sides of a subtracter. SOLUTION: The output side of a sensor 4, which is placed near a speaker 3, is connected to an A/D conversion part 5, a signal processing part 6 and a D/A conversion part 7. The output side of the part 7 is connected to one of both input terminals of a subtracter 1. A correction part consists of the parts 5, 6 and 7. As the signal of the sensor 4 that detected the output of the loudspeaker 3 has its limited feedback degree, the phase characteristic is corrected by the correction part without very much affecting the amplitude characteristic. Thus, the phase shift of a feedback signal is suppressed by the correction part, and accordingly the stable feedback operations are secured in a wide band. As a result, the distortions and the sound pressure frequency characteristic can be improved adequately with respect to the actual reproduced sounds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound reproducing apparatus having a reproduction signal feedback circuit.

[0002]

2. Description of the Related Art In a conventional sound reproducing apparatus, as a method for improving a sound reproduced from a speaker, an MFB for detecting a movement of a speaker and applying a negative feedback to a drive amplifier, a so-called motional feedback, or an AFB for applying a feedback by a reproduced sound, a so-called AFB. Acoustic feedback is known.

In both cases, by applying negative feedback, an error from the original signal can be reduced and the frequency characteristics and the distortion can be improved.

[0004]

However, in the improvement method of the conventional apparatus, the speaker load is shifted in phase by the impedance component in both the reduction and the high frequency range. The margin of feedback is lost, and it is easy to cause oscillation,
In addition, the detection unit and the detection circuit are also problematic due to factors around the phase.

[0005]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention provides a correction section for a feedback signal and performs phase correction, whereby the feedback is stably applied and the feedback effect over a wide band is obtained. It is obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention provides a subtractor connected to an input signal, a power amplifier for amplifying the output of the subtractor, and a speaker for reproducing the output of the power amplifier. And a sensor for detecting a reproduction signal, and a correction unit for correcting the output of the sensor and connected to the other input of the subtractor. The correction unit includes an A / D conversion unit, a signal processing unit, and a D / A A sound reproducing device comprising a conversion unit, which has an operation of correcting a phase rotation of a feedback signal by digital signal processing.

According to a second aspect of the present invention, in the first aspect, the signal processing section is an acoustic reproduction apparatus comprising a time axis conversion section and a digital filter, and a phase of a feedback signal is obtained by digital signal processing. It has the function of correcting rotation.

According to a third aspect of the present invention, in the second aspect of the invention, the time axis conversion unit is located before the digital time filter and the time axis reversal unit before the digital filter. This is a sound reproducing device including a post-time-time reversing unit, and has an operation of correcting a phase rotation of a feedback signal by digital signal processing.

According to a fourth aspect of the present invention, in the sound reproducing apparatus according to the third aspect, the digital filter is an infinite-length impulse response filter. It has the effect of correcting.

According to a fifth aspect of the present invention, there is provided an audio reproducing apparatus according to the fourth aspect, wherein the signal processing section obtains a right-up phase characteristic having a positive slope with respect to the frequency. Yes, it has the effect of correcting the phase rotation of the feedback signal by digital signal processing.

According to a sixth aspect of the present invention, in the second aspect of the invention, N signal processing units are connected in parallel, and the processing time lengths of the time axis processing are the same, and the respective phases are sequentially shifted. This is a sound reproducing device configured to be shifted by 1 / N time, and has an operation of correcting a phase rotation of a feedback signal by digital signal processing.

According to a seventh aspect of the present invention, in the first aspect of the present invention, the sensor is a sound reproducing device which is a microphone, and the AFB corrects the phase rotation of the feedback signal by digital signal processing. Having.

According to an eighth aspect of the present invention, in the first aspect, the sensor is a sound reproducing apparatus which is a vibration pickup for detecting vibration of a speaker.
The FB has the function of correcting the phase rotation of the feedback signal by digital signal processing.

According to a ninth aspect of the present invention, in the first aspect, the sensor is a sound reproducing device which is a sensor for detecting a driving current of a speaker, and a feedback signal is provided to the MFB by digital signal processing. Has the function of correcting the phase rotation of

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a block diagram of an audio reproducing apparatus according to Embodiment 1 of the present invention.

In FIG. 1, an input signal is connected to an input terminal of a subtracter 1, an output of the subtracter 1 is connected to an input terminal of a power amplifier 2, and an output of the power amplifier 2 is connected to an input terminal of a speaker 3. Connected. The output of the sensor 4 disposed in the vicinity of the speaker 3 is connected to an A / D converter 5, the output of the A / D converter 5 is connected to a signal processor 6, and the output of the signal processor 6 is D / D The output of the D / A converter 7 is connected to the other input terminal of the subtractor 1. In the signal processing unit 6, a pre-time axis reversing unit 8, a digital filter 9, and a post-time time reversing unit 10 are connected in this order. Here, the AD conversion unit 5, the signal processing unit 6, and the DA conversion unit 7 constitute a correction unit.

The operation of the first embodiment will be described. The signal of the sensor 4 which has detected the output of the speaker 3 has a frequency characteristic which is not flat as shown in FIG. If it is used for a signal, there is a problem in stability and band, and the degree of feedback is limited. Therefore, the correction unit should minimize the influence on the amplitude characteristic as shown in FIG.
The phase characteristic is corrected as shown in FIG. In general, the phase inclination has a right-down characteristic that lags against an increase in frequency. Therefore, it is necessary to obtain an opposite right-up characteristic in order to correct the inclination.

However, in an analog circuit, since the phase and amplitude characteristics are closely related, it is not usually possible to obtain a phase characteristic that rises to the right while keeping the amplitude constant.

As shown in FIGS. 3A and 3B, it is conceivable to use a negative resistance in the phase shift circuit. However, it is practically difficult to perform a stable operation using the negative resistance.

Therefore, once a correction characteristic is obtained by converting the signal into a digital signal, the signal is returned to an analog signal to obtain a feedback signal so that a desired characteristic is obtained by digital technology.

FIGS. 4A to 4D are explanatory diagrams of the detailed operation of the signal processing unit. The sensor signal is converted into a digital signal as shown in FIG. 4A by the A / D converter 5 and then inverted by the pre-time axis inverting unit 8 at every time interval ts.
(B) The signal is obtained.

When this signal is subjected to a high-frequency emphasis characteristic by the digital filter 9, a post-shoot signal as shown in FIG. 4C is obtained. Next, when the time axis is returned at the time interval ts by the post-time axis reversing unit 10, a preshoot signal can be obtained as shown in FIG. Here, an infinite-length impulse response filter as shown in FIG.

As described above, by interposing the digital filter 9 between the time axis reversing units 8 and 10, the inverse time characteristic signal y (t) = x (-) with respect to the original output signal x (t) of the filter unit.
t) will be obtained. Therefore, by using a digital filter as shown in FIG. 5 which simulates a conventional analog phase shift circuit in the filter section to obtain the characteristic shown in FIG.
The inverse time characteristic signal shown in FIG. 6B is obtained, and a desired right-upward phase characteristic can be realized. The signal is supplied to the D / A converter 7
After returning to the analog signal in step (1), the signal is input to the subtractor 1 and feedback is applied. However, since the phase of the feedback signal is corrected, feedback can be applied stably, and a feedback effect over a wide band can be obtained. it can.

According to the first embodiment, since the phase of the feedback signal is suppressed by the correction unit, a stable feedback operation can be obtained over a wide band. For this reason, in the feedback system which was conventionally unstable and could be applied only in a narrow band and shallow, it is possible to sufficiently apply the signal in a wide band, and it is possible to improve the distortion, the response, and the sound which are the effects of the negative feedback operation. The improvement of the pressure frequency characteristic and the like are sufficiently applied to the actual reproduced sound, and the effect is large.

(Embodiment 2) FIG. 7 is a block diagram of an audio reproducing apparatus according to Embodiment 2 of the present invention. The difference from Embodiment 1 is that two signal processing units 6, 16 are connected in parallel. Is a point. In the second embodiment, an input signal is connected to an input terminal of a subtractor 1, an output of the subtracter 1 is connected to an input terminal of a power amplifier 2, and an output of the power amplifier 2 is connected to an input terminal of a speaker 3. The output of the sensor 4 is connected to an A / D converter 5, the output of the A / D converter 5 is connected to a signal processor 6, and the output of the signal processor 6 is connected to a D / A converter 7. Connected to the D / A converter 7
Is connected to the other input terminal of the subtractor 1.

The two signal processing units 6 and 16 are connected in parallel.
The digital filter 9 and the post-time axis reversing unit 10 are connected in this order.

Similarly, the second signal processing section 16 is also connected in the order of the preceding time axis reversing section, the digital filter, and the subsequent time axis reversing section. Here, the AD conversion unit 5, the signal processing unit 6,
16, a correction unit is configured by the DA conversion unit 7.

The operation of the second embodiment will be described. In the first embodiment, the time interval ts is synchronized with the discontinuous point of the signal, but is not synchronized with the discontinuous point of the signal as shown in FIGS. When you perform various signal processing,
As a result of returning the time axis, unnecessary signals may be added at the end of the time interval ts as shown in FIG. 8D.

Therefore, an interval tsh is set anew in which the time interval ts is １ ／, and the first signal processing unit and the second signal processing unit perform the signal processing with the time interval tsh shifted. By connecting the first half of the result at every time interval tsh, an unnecessary additional signal generated at the terminal end can be avoided, and a desired processing result can be obtained. FIGS. 9A to 9D
10A to 10D show signals at each processing stage of the first signal processing unit 6, and FIGS. 10A to 10D show signals at each processing stage of the second signal processing unit 16 and show signals connected to FIG. Indicated.

Here, two signal processing units 6 and 16 are arranged in parallel. However, the same result is obtained even if the time interval thf is set to 1 / N and the shift of each processing unit is shifted by 1 / N. Can be obtained.

According to the second embodiment, the signal processing units 6
Providing a plurality of 16 makes it possible to cope with processing of a signal having many discontinuous points, and a desired signal can be obtained. Since the phase of the feedback signal is suppressed by the correction unit, a stable feedback operation over a wide band can be obtained. For this reason, in the feedback system which was conventionally unstable and could be applied only in a narrow band and shallow, it is possible to sufficiently apply the signal in a wide band, and it is possible to improve the distortion, the response, and the sound which are the effects of the negative feedback operation. The improvement of the pressure frequency characteristic is sufficiently applied to the actual reproduced sound, and the effect is great.

[0032]

As described above, according to the present invention, a system with high stability can be constructed by providing various correction units and performing correction while suppressing the phase rotation of the feedback signal. Is a great thing.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a sound reproducing device according to a first embodiment of the present invention.

FIG. 2A is a diagram showing a microphone output frequency characteristic when the device is corrected for distance; FIG. 2B is a diagram showing a microphone output frequency characteristic when the device is not corrected for distance;

3A is a circuit diagram of a phase shift circuit, and FIG.

FIG. 4 is an explanatory diagram of an operation of a correction unit of the apparatus.

FIG. 5 is a circuit diagram of an infinite-length impulse response filter used in a correction unit of the apparatus.

FIG. 6 is an explanatory diagram of the operation of the digital filter.

FIG. 7 is a block diagram showing a sound reproducing device according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram of an operation of the correction unit of the apparatus when an unnecessary signal is added.

FIG. 9 is an explanatory diagram of an operation of a first signal processing unit of the device.

FIG. 10 is an explanatory diagram of an operation of a second signal processing unit of the device.

FIG. 11 is a signal diagram corrected by a correction unit of the apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Subtractor 2 Power amplifier 3 Speaker 4 Sensor 5 A / D conversion part 6, 16 Signal processing part 7 D / A conversion part 8 Pre-time axis reversal part 9 Digital filter 10 Post-time time reversal part

Claims (9)

[Claims] 1. A subtractor connected to an input signal, a power amplifier for amplifying an output of the subtractor, a speaker for reproducing an output of the power amplifier, a sensor for detecting a reproduced signal, and an output of the sensor. And a correction unit connected to the other input of the subtractor, the correction unit including an A / D conversion unit, a signal processing unit, and a D / A conversion unit. 2. The sound reproducing apparatus according to claim 1, wherein said signal processing unit comprises a time axis conversion unit and a digital filter. 3. The sound reproducing apparatus according to claim 2, wherein the time axis conversion section comprises a front time axis reversal section provided before the digital filter and a post time axis reversal section provided after the digital filter. 4. The sound reproducing device according to claim 3, wherein said digital filter is an infinite impulse response filter. 5. The sound reproducing apparatus according to claim 2, wherein the signal processing section obtains a right-up phase characteristic having a positive slope with respect to the frequency. 6. The N signal processing units are connected in parallel, and the processing time length of the time axis processing is the same, and each phase is sequentially 1
3. The sound reproducing apparatus according to claim 2, wherein the sound reproducing apparatus is configured to be shifted by / N time. 7. The sound reproducing device according to claim 1, wherein the sensor is a microphone. 8. The sound reproducing apparatus according to claim 1, wherein said sensor is a vibration pickup for detecting vibration of a speaker. 9. The sound reproducing apparatus according to claim 1, wherein said sensor is a sensor for detecting a drive current of a speaker.