JPH03280697A - Howling eliminating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a howling removal device attached to an electronic tongue base, a karaoke device, or a general public address device.

(Prior art) As is well known, when a part of the audio output from the speaker of the audio amplification system enters the microphone, a positive feedback loop of sound is formed and the amplification system oscillates, causing the amplification system to oscillate at a certain frequency. A large-amplitude sustained sound is produced. This is Know\Uring.

As a device to prevent this unpleasant howling,
Conventionally, when howling occurs, the gain of the audio signal amplification system is temporarily lowered to suppress the howling.

(Invention or Problem to be Solved) Is it possible to suppress howling by lowering the gain of the amplification system when it occurs, or is it possible to suppress howling by lowering the gain of the amplification system when it occurs? If the conditions do not change, howling will occur again at the same frequency. In other words, although it is possible to temporarily cut off the sustained howling sound, there is a high possibility that howling will occur again when the amplification gain is returned to its original state.

This invention was made in view of the conventional problems mentioned above, and its purpose is to reduce the amplification gain even if the conditions of the acoustic system connecting the speaker and microphone are the same as when the noring occurred. To provide a howling removal device capable of continuously suppressing howling without any problem.

(Means for Solving the Problems) A howling removal device according to the present invention is inserted on a signal transmission path where /1 howling may occur, and delays a transmitted signal by a time specified by a control signal. a delay means, a howling frequency detection means for repeatedly measuring the frequency spectrum characteristics of the signal on the signal transmission path at high speed and detecting a frequency that causes howling and has a large amplitude or is sustained; and delay time control means for specifying a time corresponding to a half wavelength of the frequency to the delay means using the control signal.

(Function) When howling occurs at a certain frequency, it is detected by the detection means, and the delay time of the delay means is set to a time corresponding to a half wavelength of the detected howling frequency. As a result, the phase condition for positive feedback at the frequency that was causing the lX howling is satisfied and no longer exists, and the signal component of the /'% howling frequency fed back from the microphone becomes the opposite phase to the original signal, and the howling stops. do.

(Embodiment) FIG. 1 shows a schematic configuration of a car telephone device to which a howling removal device is added according to an embodiment of the present invention. The output signal of the microphone 1 of the handset is inputted to a transmitter 3 via an amplifier 2, and is sent out to a radio telephone line. Also, signals sent from the other party via the wireless telephone line are received by the receiver 4, passed through the amplifier 6, and then sent to the speaker 7 of the handset.
Audio is output from.

In order to apply this invention, a delay circuit 5 is inserted on the audio signal transmission path from the receiver 4 to the amplifier 6. This delay circuit 5 uses a DSP (digital signal processor), and delays the signal by a time specified by a control signal, which will be described later, before transmitting the signal.

It is assumed that the delay time is zero in the normal state.

In such a car telephone device, a portion of the audio output from the speaker 7 enters the microphone 1 on both sides of the conversation, creating a positive feedback loop, which may cause howling.

The audio signal output from the receiver 4 is also input to an FFT (fast Fourier transform) circuit 8. The FFT circuit 8 repeatedly measures the frequency spectrum characteristics of the audio signal transmitted toward the speaker 7 at high speed, and sequentially stores the measured spectrum characteristics data in the buffer 7 memory 9. The buffer memory 9 sequentially stores spectral characteristic data obtained through multiple measurements within a certain period of time. The howling frequency detection circuit 10 examines the data in the buffer memory 9, analyzes whether a state in which an extremely large amplitude continues for a certain period of time or more at a specific frequency (that is, howling) is occurring, and detects when howling has occurred. If detected, the frequency is transmitted to the delay time control circuit 11. When the delay time control circuit 11 is notified of the occurrence of howling and its frequency, the delay time control circuit 11 calculates a time corresponding to a half wavelength of the howling frequency, and causes the delay circuit 5 to delay and transmit the signal by that time. give a control signal to. As a result, the audio output generated from the speaker 7 is delayed by the above-mentioned time, the phase condition of the positive feedback loop including the telephone device of the other party no longer holds true, and the knowing at the above-mentioned frequency is stopped.

(Effects of the Invention) As explained in detail above, the 71 howling removal device of the present invention delays the signal on the signal transmission path by a half wavelength of the howling frequency when howling occurs, thereby eliminating howling. Howling is stopped by destroying the positive feedback phase conditions that cause howling, so the amplification gain of the signal transmission path can be maintained as it is during normal operation, and the audio coupling conditions between the speaker and microphone are changed to prevent howling. Even if it is the same as before, howling can be stopped by manipulating the phase of the signal using a circuit, and it is possible to continue using it at normal speed without howling.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a car telephone device equipped with a howling removal device according to an embodiment of the present invention. 1... Microphone 2... Amplifier 3... Transmitter 4... Receiver 5... Delay circuit 6...
Amplifier 7... Speaker 8... Fast Fourier transform circuit (FFT) 9...
... Buffer memory 10 ... Howling frequency detection circuit 11 ... Delay time control circuit

Claims (1)

[Claims] A delay means is inserted on a signal transmission path that is likely to cause howling and delays the transmitted signal by a time specified by a control signal, and a delay means that repeatedly measures the frequency spectrum characteristics of the signal on the signal transmission path at high speed. , a howling frequency detection means for detecting a frequency at which howling occurs and a large amplitude is sustained; and a delay time control means for specifying a time corresponding to a half wavelength of the detected howling frequency to the delay means using the control signal. Equipped with a howling removal device.