JPH0937383A - Howling preventing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a howling preventing circuit capable of effectively preventing the generation of howling at the time of connecting a microphone to a terminal or connecting an operation switch. SOLUTION: A current change on an input terminal 2 is always monitored by a current detector 3, and at the time of detecting the connection of a microphone 1 to an input terminal 2 or the connection of an operation switch, a gain controller 4 is driven based upon a control signal supplied from a pulse generator 5 and the gain of a microphone amplifier is temporarily reduced down to a prescribed level in which howling is not generated. A control signal is supplied from the pulse generator 5 again after the lapse of a prescribed interval to return the gain of the microphone amplifier to a required object value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a howling prevention circuit, and more particularly to a howling prevention circuit which is used in a microphone loudspeaker, a karaoke machine or the like and which prevents howling that occurs when a microphone is connected.

[0002]

2. Description of the Related Art In a microphone loudspeaker or the like, when a signal input from a microphone is amplified by an amplifier and output from a speaker, a part of acoustic energy dissipated from the speaker is fed back and input to the microphone. By forming a closed loop of a transmission path and repeatedly amplifying a signal in the closed loop through an amplifier, "howling", which is a kind of voice noise, occurs.

As a conventional countermeasure against howling, there is a method of installing a speaker in a region where the directional characteristic of the microphone is "null", and suppressing the acoustic energy radiated from the speaker from being fed back to the microphone.

FIG. 3 is a diagram for explaining an example of the directional characteristic of the microphone (super cardioid characteristic). The microphone is installed at the origin on the Cartesian coordinates. In this directional characteristic, the fact that the microphone does not respond to the acoustic energy radiated from the speaker installed in the part shown as the "null area" in the figure is used to determine the positional relationship between the microphone and the speaker. Prevents howling from occurring.

Further, instead of such a structural measure,
A method of providing a circuit means for canceling an echo between a microphone and a speaker is also generally adopted. For example, by connecting an echo canceller (comprising an adaptive filter, etc.) before and after an amplifier such as a microphone loudspeaker, acoustic coupling is reduced. Howling is prevented by subtracting the estimated value of the echo from the output signal.

[0006]

However, in the above-mentioned conventional structural measures, the directional characteristics of the microphones are different for each microphone, and the positional relationship between the microphone and the speaker may not be fixed. In the case of, there is a problem that it is not an effective measure.

Also, in the measures using the conventional echo canceller, the echo canceller is useful only in a limited frequency range of the signal, and the microphone terminal is connected to the input terminal of the device (terminal connection). , When the microphone operation switch is turned on (operation switch connection), the microphone can be used, but if the speaker output or the microphone amplifier gain is set to a large value, howling will be completely eliminated. There is a problem that it cannot be prevented.

The present invention has been made in view of the above problems, and an object thereof is to effectively prevent howling that occurs when a microphone terminal is connected or an operation switch is connected.

[0009]

In order to achieve the above object, the present invention provides a howling prevention circuit for preventing howling that occurs when a sound input from a microphone is amplified and output from a speaker. A howling prevention circuit comprising a detector for detecting a connection state of the microphone, and reducing the volume output from the speaker to a predetermined level when the detector detects the connection of the microphone. I will provide a.

Further, according to the present invention, when the detector detects the connection of the microphone, the volume output from the speaker is reduced to a predetermined level, and then controlled to be set to a desired value again. Provided is a howling prevention circuit.

Further, according to the present invention, when the detector detects the disconnection of the microphone, the volume output from the speaker is reduced to a predetermined level, while the connection of the microphone is detected. Provided is a howling prevention circuit characterized by controlling a volume to be set to a desired value.

In the howling prevention circuit of the present invention, a gain controller for varying the gain of the amplifier connected to the microphone is further provided, and the volume output from the speaker is increased or decreased via the gain controller. It is preferable that a control signal generator for supplying a control signal for varying the gain of the amplifier to the gain controller be further provided.

In the howling prevention circuit of the present invention, if the detector detects a change in current at an input terminal to which a terminal of the microphone is connected, the detector detects connection and / or disconnection of the microphone. Good.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

[0015]

First Embodiment FIG. 1 is a block diagram for explaining the structure of a howling prevention circuit according to a first embodiment of the present invention.

Referring to FIG. 1, in the present embodiment, a microphone 1 for converting an input audio signal into an electric signal and outputting the electric signal is connected to a terminal (jack or the like, not shown) of the microphone 1. Input terminal 2, a current detector 3 that detects a change in current at the input terminal 2, and an amplification factor (“gain”) of a microphone amplifier (not shown) that amplifies an electric signal captured through the input terminal 2. (Hereinafter also referred to as “)”, a pulse generator 5 for generating a control signal in a pulse form (control pulse) for increasing or decreasing the gain of the microphone amplifier with respect to the gain controller 4, and a pulse generator. 5 is provided with a timing generator 6 for supplying a reference signal, and a speaker 8 for converting the amplified electric signal into an audio signal and outputting the audio signal.

In FIG. 1, a current detector 3 is connected to an input terminal 2 to which a terminal of a microphone 1 is connected, and a change in current at the input terminal 2 is constantly monitored.

The current detector 3 turns on the operation switch when the terminal of the microphone 1 is connected to the input terminal 2.
When a change in the current that occurs when is set is detected, the pulse generator 5 is driven to send a control pulse to the gain controller 4, and the gain of the microphone amplifier is once reduced to a predetermined level at which howling does not occur.

After a predetermined interval, the pulse generator 5 again generates a control pulse based on the reference signal supplied from the timing generator 6, and controls the gain controller 4 to change the gain of the microphone amplifier. The microphone 1 is returned to a predetermined desired value at predetermined intervals.
The input signal from is output from the speaker 8 with a sufficient volume.

By adopting the circuit configuration as described above, according to the present embodiment, howling that occurs when the microphone 1 is connected to the terminals or the operation switch is connected can be effectively prevented.

[0021]

Second Embodiment FIG. 2 is a block diagram for explaining the structure of a howling prevention circuit according to a second embodiment of the present invention.

With reference to FIG. 2, in this embodiment, a microphone 1 for converting an input audio signal into an electric signal and outputting the electric signal is connected to a terminal (jack or the like, not shown) of the microphone 1. Input terminal 2, a current detector 3'for detecting a change in current at the input terminal 2, and a gain of a microphone amplifier (not shown) for amplifying an electric signal taken in through the input terminal 2 are variably controlled. Gain controller 4 and an up counter 7 for generating a control signal for increasing the gain of the gain controller 4.
And a speaker 8 for converting the amplified electric signal into a sound signal and outputting the sound signal.

In the first embodiment, the gain of the microphone amplifier is increased or decreased when the terminals of the microphone 1 are connected or when the operation switch is connected. However, in the present embodiment, as shown in FIG.
The gain of the microphone amplifier is variably controlled not only when the microphone is connected but also when the microphone 1 is disconnected.

That is, the current detector 3'includes the input terminal 2
From the microphone 1 and the disconnection of the operation switch are detected, and at the time when these disconnections of the microphone 1 are detected, the current detector 3 ′ directly drives the gain controller 4 and howling the gain of the microphone amplifier occurs. The level is lowered to a predetermined level that does not exist (down control).

On the other hand, when the current detector 3'detects the connection of the microphone 1, the gain controller 4 is controlled by the up counter 7 after a predetermined time delay, and the gain of the microphone amplifier is predetermined at predetermined intervals. Return to desired target value (up control).

The pulse generator 5 and the timing generator 6 used in the first embodiment are provided instead of the up counter 7 of the present embodiment, and the microphone 1 is used.
When the disconnection is detected, the gain of the microphone amplifier may be reduced based on the control pulse supplied at a predetermined interval.

By adopting the circuit configuration as described above, according to the present embodiment, howling that occurs when the microphone 1 is connected to the terminal or the operation switch is connected can be effectively prevented, and when the terminal is disconnected. In addition, since the gain of the microphone amplifier is lowered to a predetermined level, it is possible to shorten the time until the volume output from the speaker 8 is properly set.

In the first and second embodiments, the case where the output of the speaker is suppressed by the gain controller 4 increasing or decreasing the gain of the microphone amplifier is described as an example. Even when an amplifier is provided separately from the microphone amplifier, the same control as the control described in each of the above embodiments can be performed on this amplifier.

However, when there is a signal input to the speaker 8 in addition to the audio signal input from the microphone 1, for example, the audio input from the microphone and the C
In the case of a karaoke device or the like that outputs a music performance by a D player or the like from the same speaker, in the sense that howling can be prevented without affecting the output of signals other than the microphone, the method described in each of the above embodiments is used. It is preferable to control the gain of the microphone amplifier.

Although some embodiments of the present invention have been described above, the present invention is not limited to these embodiments and includes various embodiments according to the principle of the present invention.

[0031]

As described above, according to the present invention,
It is possible to effectively prevent howling from occurring when the output of the speaker is set to a large value when the microphone is connected.

Further, according to the present invention, when the disconnection of the microphone is detected, the volume output from the speaker is lowered in advance to a predetermined level, so that the time required to set the volume to a desired value can be reduced. Can be shortened.

Further, according to the present invention, by varying the gain of the amplifier connected to the microphone to increase or decrease the volume output from the speaker, it is possible that there is sound input to the speaker from other than the microphone. In this case, howling can be prevented without affecting the output of the sound.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of a howling prevention circuit according to a first embodiment (Embodiment 1) of the present invention.

FIG. 2 is a block diagram for explaining a configuration of a howling prevention circuit according to a second embodiment (Embodiment 2) of the present invention.

FIG. 3 is a diagram illustrating an example of a directional characteristic of a microphone (super cardioid characteristic).

[Explanation of symbols]

 1 Microphone 2 Input Terminals 3, 3'Current Detector 4 Gain Controller 5 Pulse Generator 6 Timing Generator 7 Up Counter 8 Speaker

Claims (6)

[Claims] 1. A howling prevention circuit for preventing howling that occurs when a sound input from a microphone is amplified and output from a speaker, comprising a detector for detecting a connection state of the microphone. When the detector detects the microphone connection,
A howling prevention circuit, which reduces the volume output from the speaker to a predetermined level. 2. When the detector detects the connection of the microphone, the volume output from the speaker is reduced to a predetermined level, and then the volume is controlled to a desired value again. The howling prevention circuit according to claim 1. 3. When the detector detects disconnection of the microphone, the volume output from the speaker is reduced to a predetermined level, and when the connection of the microphone is detected, the volume is set to a desired level. The howling prevention circuit according to claim 1, wherein the howling prevention circuit is controlled to be set to a value. 4. A gain controller for varying the gain of an amplifier connected to the microphone, further comprising: increasing or decreasing a volume output from the speaker via the gain controller. The howling prevention circuit according to any one of the above. 5. The howling prevention circuit according to claim 4, further comprising a control signal generator for supplying a control signal for varying the gain of the amplifier to the gain controller. 6. The method according to claim 1, wherein the detector detects a connection and / or a disconnection of the microphone by monitoring a change in current at an input terminal to which a terminal of the microphone is connected. The howling prevention circuit according to any one of the above.