JPH0426237A - Dark noise detecting method and automatic level control loud-speaking system for sound field - Google Patents

Abstract

PURPOSE:To easily monitor the level of dark noise in a sound field by comparing the sound field monitor signal of a sound field monitoring sound collector with a line signal in proportion to the output of an amplifier to drive a loudspeaker, obtaining a loud-speaking sound signal after separating the same waveform component,and using the difference between the sound field monitor signal and the loud-speaking sound signal as a dark noise signal. CONSTITUTION:A sound field monitor sound collector 3 is provided to extract the line signal in proportion to the output from an amplifier to drive a loudspeaker 4 in a sound field 20, and to sense a loud-speaking tone from the loudspeaker 4 in the sound field 20 and the dark noise of the sound field 20. Then, the loud-speaking sound signal is formed after separating the same waveform component as the waveform of the line signal in the output of the sound field monitor sound collector 3, and the difference between the output of the sound field monitor sound collector 3 and the loud-speaking sound signal is used as the dark noise signal so as to detect the level of the dark noise signal. Thus, the level of the dark noise in the sound field can be easily detected.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for detecting background noise in a sound field and an automatic level control public address system, and in particular, to a method for detecting background noise in a sound field, and in particular, to perform a call broadcast, background music broadcast, emergency broadcast, masking broadcast, etc. in spaces inside and outside a building at a level that is always higher than the background noise level by a certain level. Concerning automatic level control public address systems.

[Conventional technology]

When controlling the loudspeaker sound level in a space where loudspeaker broadcasting is performed (hereinafter referred to as a sound field), the following method has conventionally been mainly used, but the control at that time is performed manually. (1) The loudspeaker input power is adjusted by adjusting the amplifier output of the loudspeaker broadcasting device, and the loudspeaker sound level of the sound field is controlled. (2) Adjust the speaker input power by adjusting the attenuator connected to the speaker, and control the amplified sound level of the sound field.

[Problem to be solved by the invention]

If there is no change in the background noise level in the sound field or if there is only a small change, once adjustment is made by the above-mentioned manual control, loudspeaker broadcasting at an appropriate level can be maintained for a considerable period of time without any problem. However, if the background noise level of the sound field changes significantly, especially if it occurs frequently, frequent manual adjustments are required to make the loudspeaker broadcast clear, effective, and comfortable. In reality, due to various difficulties such as difficulty in securing skilled operating personnel, adjustments are rarely made to follow changes in background noise and ensure that the amplified sound level is always at least a certain level higher than background noise. . In this case, effective and comfortable public address broadcasting in a sound field with changes in background noise cannot be expected. Therefore, an object of the present invention is to provide a simple method for detecting background noise in a sound field and to provide an automatic level control public address system that maintains the amplified sound level higher than the background noise by a required difference even if the background noise level changes. be.

[Means to solve the problem]

Referring to the embodiments of FIGS. 1 and 2, the method for detecting background noise in a sound field of the present invention extracts a line signal proportional to the amplifier output from an amplifier 2 that drives a speaker 4 in a sound field 20. , amplified sound from the speaker 4 and the sound field 20 in the sound field 20
A sound field monitoring sound collector 3 sensitive to background noise is provided, and a component having the same waveform as the line signal in the output of the sound field monitoring sound collector 3 is separated to produce an amplified sound signal, and the sound field monitoring A configuration is used in which the difference between the output of the sound collector 3 and the amplified sound signal is used as a background noise signal, and the level of the background noise signal is detected. Also, according to the automatic level [11 public address system of the present invention]
A sound field monitoring sound collector 3 is provided in a sound field 20 in which a speaker 4 driven by an amplifier 2 is arranged, and a line signal terminal 2C for generating a line signal proportional to the output of the amplifier 2 is provided on the amplifier 2. . A required value for the difference between the amplified sound level and the background noise level is set in the level difference setting device 15. A waveform comparison circuit 9 is connected to the line signal terminal 2C of the amplifier 2 and the sound field monitoring sound collector 3, and detects and separates components of the same waveform as the line signal waveform in the output of the sound field monitoring sound collector 3. The difference between the output of the sound field monitoring sound collector 3 and the amplified sound signal is used as a background noise signal. The level of the background noise signal is detected by the background noise level circuit 11, the level of the amplified sound signal is detected by the amplified sound level circuit 12, and the difference between the output of the background noise level circuit 11 and the output of the amplified sound level circuit 12 is determined as a level. It is determined by the difference circuit 13. A 1IillI+ signal corresponding to the difference between the output of the level difference circuit 13 and the setting value of the level difference setting device 5 is obtained by the control signal generation circuit 14, and the control signal is applied to the amplifier 2.

[Operation] In the above embodiment, amplified sound is sent from the sound source device 1 to the sound field 20 via the amplifier 2 and the speaker 4. The sound field monitoring sound collector 3 is, for example, a microphone installed in the sound field 20 at a position at the height of the human ear, and detects the sum of the amplified sound reaching that position from the speaker 4 and the background noise at that position. Output. This sum is added to the sound field monitoring input terminal 5b of the controller 5. The signal applied from the line signal terminal 2c of the amplifier 2 to the line signal terminal 5a of the controller 5 is proportional to the output of the amplifier 2 and thus to the amplified sound applied to the sound field 20 via the loudspeaker 4. The waveform comparison circuit 9 in the fsal device 5 is connected to the line signal terminal 2c of the amplifier 2 via the line signal input terminal 5a, and is also connected to the sound field monitoring sound collector 3 via the sound field monitoring input terminal 5b. Then, a component having the same waveform as the line signal waveform in the output of the sound field monitoring sound collector 3 is detected and separated to form an amplified sound signal. If the difference between the output of the sound field monitoring sound collector 3 and the amplified sound signal is calculated, this corresponds to a background noise signal. Background noise level circuit 11
By determining the level of the background noise signal using , the background noise level of the sound field 20 can be detected. Furthermore, in the automatic level control public address system of the present invention,
First, a desired value for the difference between the sound field audio level and the background noise level is set in the level difference setting device 15, and
and sends amplified sound to the sound field 20 via the speaker 4. The sound field monitoring sound collector 3 is, for example, a microphone installed in the sound field 20 at the height of the human ear, and the speaker 4
outputs the sum of the amplified sound arriving at that position and the background noise at that position. Sound field monitoring input terminal 5b of controller 5
This sum is added to . Line signal terminal 2 of amplifier 2
The line signal applied from C to the line signal terminal 5a of the controller 5 is proportional to the output of the amplifier 2 and is therefore proportional to the output of the speaker 4.
It is proportional to the amplified sound added to the sound field 20 via . The waveform comparison circuit 9 in the controller 5 has a line signal power terminal 5a.
is connected to the line signal terminal 2c of the amplifier 2 via the sound field monitoring input terminal 5b, and to the sound field monitoring sound collector 3 via the sound field monitoring input terminal 5b.
A component having the same waveform as the line signal waveform in the output of the sound field monitoring sound collector 3 is detected and separated, and this is used as an amplified sound signal. Further, the difference between the output of the sound field monitoring sound collector 3 and the amplified sound signal is defined as a background noise signal. Since the output of the sound field monitoring sound collector 3 corresponds to the sum of the amplified sound and the background noise in the sound field as described above, the background noise signal obtained as described above corresponds to the sum of the amplified sound and the background noise in the sound field 20. It corresponds to noise. The level of the background noise signal from the waveform comparison circuit 9 is determined by the background noise level circuit 11, and the level of the amplified sound signal is determined by the amplified sound level circuit 12. A level difference circuit 13 provides a difference between the background noise level and the amplified sound level. Since the signal output of the control signal generation circuit 14 takes a value corresponding to the difference between the output of the level difference circuit 13 and the setting value of the level difference setting device I5, the measured value of the difference between the loudspeaker sound and the background noise is the difference. Indicates how far away from the set value the value is. Therefore, using the output of the control signal generation/output circuit 14 as a control signal for the amplifier 2 is nothing but feedback control of the difference between the amplified sound and the background noise. That is, the amplified sound level sent out from the speaker 4 is automatically controlled to a value higher than the background noise level by the value set in the level difference setting device 15. In this way, the purpose of the present invention is to provide a simple method for detecting background noise in a sound field, and to provide an automatic level control loudspeaker that maintains the loudspeaker level higher than the background noise by a required difference even if the background noise level changes. Provision of System J is realized. [Embodiment] The configuration of an embodiment of the present invention will be explained with reference to a conceptual diagram in FIG. 1 and a block diagram in FIG. 2. The sound source device 1 includes, for example, a tape deck, a recording and reproducing bag fla such as a record player chime, and a microphone lb.
It is not limited to this example. The output of the sound source device 1 is connected to a sound source input terminal 2a of an amplifier 2, amplified to a required level, and then applied to a speaker 4 via an audio output terminal 2b. The amplifier 2 used in the present invention has basically the same structure as a conventional loudspeaker broadcasting amplifier, but has the following functions not found in the conventional one. (a) A line signal proportional to the output of the audio output terminal 2b is given to the line signal terminal 2c. (b) A control signal from the controller 5 is received at the control input terminal 2d, and the amplifier output signal level at the audio output terminal 2b is controlled to a value corresponding to the control signal. The sound field monitoring sound collector 3 may be, for example, a microphone, as long as it can collect the sum of the background noise level and the amplified sound level in the sound field 20, and does not necessarily need to be installed in the position shown in FIG. . The speaker 4 is similar to a conventional one. The basic function of the controller f5 is as follows. i) Setting a desired value for the difference between the amplified sound level and the background noise level. ii) From the output of the sound field monitoring sound collector 3 to the line signal terminal 2
A component corresponding to the waveform of the output signal of c is detected, a loudspeaker signal is output by separating the component, and a background noise signal is output by calculating the difference between the output of the sound field monitoring sound collector 3 and the loudspeaker signal. 1ii) Determine the levels of the background noise signal and loudspeaker signal thus output. iv) Calculate the difference between the obtained background noise level and amplified sound level. (2) A control signal is formed from the difference between the level difference thus obtained and the set value of the difference, and is output to the control signal output terminal 5C. FIG. 2 shows a block diagram of one embodiment that performs these functions. By setting the difference between the desired amplified sound level and the background noise level as a set value on the level difference setting device 15, the function i) above is achieved. The delay circuit 6 temporally delays the line signal from the amplifier 2 to achieve synchronization with the sound field monitoring signal from the sound field monitoring sound collector 3. Therefore, the delay time is variable within a range of 0-1 seconds, for example. In the illustrated example, the delayed line signal is converted into a digital signal by an analog-to-digital (A/D) converter 7 and applied to a digital waveform comparison circuit 9 . However, the present invention is not limited to digital formats. The sound field monitoring signal from the sound field monitoring sound collector 3 is amplified by a monitoring signal amplifier 8, converted into a digital signal by an (A/D) converter 7, and then applied to a waveform comparison circuit 9. However, digitization is not a necessary requirement. The waveform comparison circuit 9 compares the line signal and the sound field monitoring signal and detects each signal component. Therefore, the circuit 9 includes a correlation circuit, a synchronization circuit, a comparison circuit, and the like. The waveform comparison circuit 9 synchronizes and compares the sound field monitoring signal and the line signal, detects and separates the same waveform portion as the line signal in the sound field monitoring signal, and generates an amplified sound signal, which is used for sound field monitoring. By using the difference between the output of the sound collector 3 and the amplified sound signal as a background noise signal, the function ii) above is achieved. The functions of the control circuit 10 for processing the output signal of the waveform comparison circuit 9 are shown by the background noise level circuit 11, the amplified sound level circuit 12, the level difference circuit 13, and the control signal generation circuit 14 in FIG. This control circuit 10 determines the level of the background noise signal and the level of the amplified sound, calculates the difference between the two levels,
The functions 1ii), iv) and V) above are achieved by outputting a control signal from the control signal generator circuit 14 based on a comparison between the calculated level difference and the setting on the level setter 15. The above functional circuits, that is, the background noise level circuit 11, the amplified sound level circuit 12, the level difference circuit 13, etc., are connected to the control j circuit 10.
is a digital expression, various calculation means and 1/1
Octave band digital filter (63H
z, 125Hz, 250Hz, 500Hz, 1k
Hz, 2kHz, 4kHz, 8kHz), etc. In FIG. 1, the amplifier 2 adjusts the output at the audio output terminal 2b according to the control signal from the I' controller 5, that is, from the control circuit 10, so that the amplified sound level in the sound field 20 is lower than the background noise level. Always control the required value as high as possible. In reality, if the amplified sound output from the speaker 4 is made excessively loud or changes extremely rapidly in response to changes in background noise, a sense of discomfort will result. To avoid this problem, in actual control, instead of adjusting the amplifier 2 to follow the instantaneous values of the background noise level and the loudspeaker level in real time, the average value within a certain time is calculated for each level. It is desirable to calculate the MH multiplied signal for amplifier 2 from the difference between the average values of . The time for calculating this average value preferably differs depending on the type of sound of the amplification broadcast, ie, voice or music. For example, a longer time is selected for the music mode and a shorter time is selected for the audio mode. Moreover, the optimum values of these times can be determined experimentally. Furthermore, in actual control, the difference DdB between the loudspeaker sound level and the background noise level is given a slight width a, and the difference between the two levels is (DdB).
It is desirable not to adjust the amplifier 2 when it is within the range of ±a) dB. Considering the dynamic range of music, it is also possible to select the width a to be large in the music mode and small in the audio mode. The present invention is not limited to the illustrated embodiment, and various modifications can be made within the technical scope thereof. For example, 2nd v! The A/D converter 7 of J is omitted and the waveform comparison circuit 9 and below are analog circuits, a plurality of sound field monitoring sound collectors 3 are provided and the background noise of the sound field 20 is obtained by summing their outputs, and the amplifier It is conceivable to provide a compensation circuit for attenuation during the period from the sound field sound collector 3 through the speaker 4. [Effects of the Invention] As explained in detail above, the method for detecting background noise in a sound field according to the present invention uses a sound field monitoring signal that is the output of a sound field monitoring sound collector installed in the sound field, and a sound field monitoring signal that is the output of the sound field monitoring sound collector installed in the sound field. Compare the line signal proportional to the output of the amplifier that drives the speaker, separate the waveform component that is the same as the line signal waveform in the sound field monitoring signal to generate an amplified sound signal, and calculate the difference between the sound field monitoring signal and the amplified sound signal. is used as a background noise signal, and furthermore, the automatic level control public address system according to the present invention uses the background noise signal to always raise the level of the amplified sound output from the speaker by a certain value higher than the background noise level of the sound field. Since it maintains the temperature, it has the following effects. (a) The background noise level of the sound field can be continuously monitored using a simple device. (b) The loudspeaker sound level is always kept a certain value higher than the background noise level, and clear and effective loudspeaker broadcasts (background music broadcasts, paging broadcasts, emergency broadcasts, masking broadcasts, etc.) can be provided. (c) Easily adjust the response characteristics to the difference between the background noise level and the amplified sound level and the level sampling time, etc. depending on whether the sound source is music or voice, and provide appropriate amplification according to the type of sound source. Can broadcast.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of the present invention, and FIG. 2 is a block diagram of a controller. DESCRIPTION OF SYMBOLS 1...Sound source device, 2...Amplifier, 3...Sound field monitoring sound collector, 4...Speaker, 5...Controller, 6.
... Delay circuit, 7... A/D converter, 8... Supervisory signal amplifier, 9... Waveform comparison circuit, 10... Control circuit, 11... Background noise level circuit, 12...・
Amplified sound level circuit, 13...Level difference circuit, 14
...1III signal generation circuit, 15...level difference setter, 20...sound field.

Claims (2)

[Claims] (1) Extract a line signal proportional to the amplifier output from an amplifier that drives a speaker in the sound field, and install a sound field monitoring sound collector in the sound field that is sensitive to the amplified sound from the speaker and the background noise of the sound field, and A component having the same waveform as the line signal in the output of the sound field monitoring sound collector is separated to form a loudspeaker signal, and a difference between the output of the sound field monitoring sound collector and the loudspeaker signal is taken as a background noise signal. , a method for detecting background noise in a sound field, comprising detecting the level of the background noise signal. (2) A sound field monitoring sound collector installed in a sound field in which a speaker driven by an amplifier is placed; a line signal terminal on the amplifier that generates a line signal proportional to the output of the amplifier; amplified sound level and background noise; A level difference setting device for setting the difference between the level and the level; connected to the line signal terminal of the amplifier and the sound field monitoring sound collector, and configured to set a component of the same waveform as the line signal waveform at the output of the sound field monitoring sound collector. a waveform comparison circuit that detects and separates the signal into a loudspeaker signal, and uses the difference between the output of the sound field monitoring sound collector and the loudspeaker signal as a background noise signal; a background noise level circuit that detects the level of the background noise signal; A loudspeaker level circuit that detects the level of the loudspeaker signal; a level difference circuit that determines the difference between the output of the background noise level circuit and the output of the loudspeaker level circuit; and the output of the level difference circuit and the level difference setter. An automatic level control public address system comprising: a control signal generation circuit that calculates the difference between the set value of the signal and the set value of the signal and applies the signal to the amplifier.