JPH0644724B2 - Howling detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a howling detection device in a loudspeaker system at a lecture or a conference, a teleconference system, or the like.

2. Description of the Related Art In recent years, in addition to lectures and conferences, systems using a loudspeaker such as a teleconference system have been developed, and a clear and natural voice transmission with a sufficient loudness is desired. .

However, in reality, there is a risk of howling, so that the loudness of the loudness cannot be raised sufficiently, and only the loudness of the loudness is low and the degree of intelligibility is poor. Because howling grows rapidly once it begins to grow,
The maximum output of the loudspeaker is reached in a short time. Therefore, absolute howling should not occur during the operation of the loudspeaker, and therefore the gain of the loudspeaker is usually set to be sufficiently low in advance. In particular, when used by general users such as in lectures and conferences, and when the acoustic characteristics of the sound field change drastically, the gain must be kept even lower.

Maximum gain within the range that does not cause howling the loudspeaker,
That is, when operating at the maximum loudness volume, howling will occur even if the acoustic characteristics of the sound field are slightly changed. Therefore, in order to operate the loudspeaker in this state, howling is detected at an early stage of its occurrence,
There is a need for a technology that automatically controls the gain and frequency characteristics of a loudspeaker.

Research on this technique has been made in the past, and one example is the howling suppression device by Matsumoto et al. (Proceedings of the Spring Meeting of the Acoustical Society of Japan 1983, P313) The conventional howling detection apparatus described above will be described with reference to the drawings.

FIG. 4 shows the structure of a conventional loudspeaker incorporating a howling detection device. In FIG. 4, 41 is a microphone, 42 is a howling detection device, 421 is a frequency analysis unit that analyzes the frequency of the output signal of the microphone 41, 422 is a determination unit that determines the occurrence of howling from the frequency analysis result, and 43 is howling. A gain control unit that lowers the gain of the loudspeaker when it occurs, 44 is a power amplifier, 4
Reference numeral 5 is a speaker. In the loudspeaker apparatus of FIG. 4, the howling detection apparatus 42 is composed of a frequency analysis unit 421 and a determination unit 422.

The operation of the loudspeaker incorporating the howling detection apparatus configured as described above will be described below.

The voice signal of the speaker is picked up by the microphone 41, amplified by the power amplifier 44, and then amplified by the speaker 45.
Since the acoustic coupling between the microphone 41 and the speaker 45 cannot be reduced to zero, the amplified voice signal is transmitted again to the microphone 4
The sound is absorbed at 1, amplified, and then amplified again by the speaker 45, and a feedback loop is formed. This is the cause of howling, and causes an oscillating phenomenon, that is, howling at a frequency where the gain of the feedback loop exceeds 1.

On the other hand, the output signal of the microphone 41 is the frequency analysis unit 42.
The frequency analysis is performed at 1, and the result is sent to the determination unit 422. The determining unit 422 uses the property that the howling sound is closer to a pure sound than the sound, and determines that howling has occurred when a frequency analysis result that energy is concentrated in a narrow frequency band is obtained. The determination result is sent to the gain adjusting section 43. This criterion is that the ratio between the energy of a certain frequency band and the energy of the frequency bands on both sides of the frequency band is larger or smaller than a preset threshold value. If the ratio is large, howling is occurring in that frequency band. judge. If it is determined that howling is occurring, then the gain adjusting unit 43 reduces the gain of the loudspeaker system to suppress howling.

Problems to be Solved by the Invention However, with the above-mentioned howling detection device, detection cannot be performed until the howling has grown considerably.
This is because the voice is also quite pure in the vowel part, and it was impossible to completely separate and detect the voice and the howling sound in the early stage of howling growth. For this reason, the conventional loudspeaker incorporating the howling detection device has a drawback that howling is considerably strong, though in a short time.

In view of the above problems, the present invention provides a howling detection device that detects howling when it is about to occur or at an early stage of its growth.

Means for Solving the Problems In order to achieve this object, a howling detection apparatus of the present invention detects a signal section immediately after a syllable of a voice included in a signal of a loudspeaker from a change in amplitude of a signal of the loudspeaker. The section energy detection section, the frequency analysis section that performs frequency analysis of the signal of the loudspeaker, the section detection result of the section detection section and the frequency analysis result of the frequency analysis section, and the signal energy of the signal section immediately after the syllable of the voice. Is concentrated in a narrow frequency band, and is not included.

Operation With this configuration, avoiding the signal section of the syllable part where the sound energy is concentrated in the signal of the loudspeaker, the signal section immediately after the syllable where the sound energy is low and the howling energy is concentrated is used. Howling can be detected using only the frequency analysis result of the signal, and a howling detection apparatus with less erroneous detection due to voice can be realized. As a result, the accuracy of howling detection is dramatically improved, and howling can be detected at an early stage of its growth, which is not conspicuous yet.
By combining with a howling suppressing device such as automatic control of the gain of the loudspeaker, it becomes possible to realize a loudspeaker that completely prevents howling. In addition, since howling can be detected and suppressed in advance, the initial setting value of the gain of the loudspeaker can be set near the howling limit, which leads to an increase in loudness.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of a howling detection apparatus according to an embodiment of the present invention.

In FIG. 1, 1 is an input terminal of a signal, 2 is a section detection unit that detects a signal section immediately after a syllable of a voice included in the input signal from an amplitude change of the input signal, and 11 is a short-term average amplitude of the input signal. Amplitude calculation unit to be obtained, 12 is a differentiating circuit for obtaining a differential value of the short-time average amplitude, 3 is a frequency analyzing unit for performing frequency analysis of the input signal, 4 is a result of the section detecting unit 2 and the frequency analyzing unit 3, When the energy of the signal in the section immediately after the syllable of is concentrated only in a narrow frequency band,
A determination unit 5 that determines howling is occurring in this frequency band is an output terminal for the determination result.

The operation of the howling detection apparatus configured as described above will be described below.

First, the output signal of the microphone of the loudspeaker is input terminal 1
And is supplied to the section detector 2. In the section detecting section 2, first, the amplitude calculating section 11 obtains the short-time average amplitude of the input signal, then the differentiating circuit 12 calculates the differential value, and the result is sent to the judging section 4. Further, the input signal is frequency-analyzed by the frequency analysis unit 3, and the result is also sent to the determination unit 4. The determination unit 4 determines that the period in which the differential value sent from the differentiating circuit 12 is negative is the section immediately after the syllable, and the analysis result sent from the frequency analysis unit 3 is the same as the conventional example for this section only. To analyze whether howling is occurring or not. However, as will be described later, since there is little risk of erroneous detection due to voice, the criterion is set so that detection can be performed with higher sensitivity than before.

Next, the operation of the section detector 2 will be described in more detail.

The signal waveform of the input terminal 1 is shown in FIG. In FIG. 2, 21 is an input signal waveform in a state where no howling is occurring, 22 is a howling margin of 3 dB,
The input signal waveform is in a slightly howling state. In the state of the howling margin of 3 dB, the howling did not continue or grow, and a weak howling sound was sometimes felt, and the howling sound also immediately attenuated.

Comparing the two waveforms, it can be seen that immediately before the howling, a signal component due to the howling occurs immediately after the syllable of the voice. Therefore, if frequency analysis is performed only on the signal section including many howling components immediately after the syllable, it becomes possible to perform howling detection with high accuracy without being disturbed by voice. The present invention realizes exactly this principle.

Through many experiments, we found that the signal section containing a lot of howling components immediately after the syllable can be detected by monitoring the amplitude change of the signal of the loudspeaker. That is, it was found that the section containing many howling components immediately after the syllable coincides with the monotonically decreasing section following the rapid increase in amplitude. The embodiment of FIG. 1 employs a method of detecting a monotonically decreasing section of the amplitude by utilizing the differential value of the short-time average amplitude of the signal.

The principle of detection of the signal section immediately after the syllable is shown in FIG. In FIG. 3, 31 is a howling margin 3d in FIG.
It is the same as the input signal waveform 22 of B, 32 is the short-time average amplitude of this input signal waveform 31 obtained by the amplitude calculator 11, and 33 is the differential value of the short-time average amplitude 32 obtained by the differentiating circuit 12. Is. This differential value 33 and the input signal waveform 3
When 1 is compared, the differential value 33 is always negative in the section immediately after the syllable. Therefore, it is understood that the section can be detected by the positive / negative of the output of the differentiating circuit. The determination unit 4 receives the output from the differentiating circuit 12, analyzes the analysis result sent from the frequency analysis unit 3 in the same manner as in the conventional example only in the negative section of the output, and determines howling.

As described above, according to the present embodiment, by providing the section detection unit, the frequency analysis unit, and the determination unit, the howling detection accuracy can be dramatically improved. By combining with a howling suppression device such as automatic gain control, it is possible to realize a loudspeaker that completely prevents howling.

EFFECTS OF THE INVENTION As described above, according to the present invention, a section detecting unit that detects a signal section immediately after a syllable of a voice included in a signal of a loudspeaker from a change in the amplitude of a signal of the loudspeaker, and a voice booster. A frequency analysis unit that performs frequency analysis of the signal, receives the section detection result of the section detection unit and the frequency analysis result of the frequency analysis unit,
Avoid the signal section of the syllable section where the energy of the voice is concentrated by configuring it with the judgment section that judges whether the energy of the signal in the signal section immediately after the syllable of the voice is concentrated in a narrow frequency band or not. , Howling judgment can be made only by using the frequency analysis result of the signal in the signal section immediately after the syllable where the energy of the speech is low and the energy of the howling is concentrated, and there are few false detections due to the speech. A howling detector has become feasible.

As a result, the accuracy of howling detection is dramatically improved, and howling can be detected at an early stage of growth where the howling is still inconspicuous. As a result, a loudspeaker system that completely prevents howling can be realized.
Further, since howling can be detected and suppressed in advance, the initial setting value of the gain of the loudspeaker can be set near the howling limit, which leads to an increase in loudness and the practical effect thereof is great.

[Brief description of drawings]

FIG. 1 is a block diagram showing the structure of a howling detection apparatus according to an embodiment of the present invention, FIG. 2 is a waveform diagram of an input signal of the howling detection apparatus, and FIG. 3 is an explanatory view of the principle of section detection.
FIG. 4 is a block diagram of a conventional howling detection apparatus and a loudspeaker using the same. 2 ... section detection unit, 3 ... frequency analysis unit, 4 ... determination unit, 11 ... amplitude calculation unit, 12 ... differential circuit.

Claims (1)

[Claims] 1. A section detector for detecting a signal section immediately after a syllable of a voice included in a signal of the loudspeaker, from a change in the amplitude of the signal of the loudspeaker, and a frequency analysis of the signal of the loudspeaker. A frequency analysis unit for performing the section detection result of the section detection unit and the frequency analysis result of the frequency analysis unit, whether the signal energy of the signal section immediately after the syllable of the voice is concentrated in a narrow frequency band, A howling detection apparatus comprising: a determination unit that determines whether or not there is any.