JP2744095B2 - Active silencer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Field of Industrial Application) The present invention relates to an active silencer that silences noise and the like actively.

(Prior Art) Recently, much attention has been paid to how to eliminate noise. Various proposals have been made for this. The use of active silencers is one of them.

The active silencer is configured to actively muffle sound at a control target point by controlling an electroacoustic transducer with a signal obtained by processing an acoustic signal detected by a sensor with a signal processing device. I have.

FIG. 3 shows an example in which an active silencer is used to prevent the drive noise of the compressor from leaking out of the machine room of the electric refrigerator to the outside. That is, in the drawing, reference numeral 1 denotes a duct constituting the machine room, 2 denotes an opening for exhaust heat provided in the duct 1, and 3 denotes a compressor housed in the duct 1. Compressor 3 is usually
Generates noise. This noise leaks outside through the opening 2. Therefore, a harsh compressor sound can be heard near the electric refrigerator. Therefore, the active silencer 11 is used to prevent sound from leaking from the opening 2 to the outside. The active silencer 11 is a sensor such as a microphone.
The compressor sound is detected at 12, the detected signal is processed by the signal processing device 13, and the processed signal is used to drive an electroacoustic transducer 14 such as a speaker. At this time, the signal processing device 13
Creates a control signal that causes the electroacoustic transducer 14 to output an additional sound having the same amplitude and opposite phase as the compressor sound in the opening 2.

By the way, such an active silencer 11 normally causes the digital signal processor to generate an additional sound signal in the signal processor 13. That is, the sensor
The signal detected at 12 is digitized by an A / D converter, and the digital signal is subjected to filter operation processing by a digital filter, and the result is converted to an analog signal by a D / A converter.
Give to. The filter characteristics are obtained by measurement or calculation, and are set in advance as digital filter coefficients. Some devices employ an adaptive filter system that adaptively updates digital filter coefficients so as to maximize the silencing effect.

However, the active silencer configured as described above has the following problems. That is, in the case where the level of the noise generated from the noise source changes with time, in order to mute using the digital signal processor, it is necessary to select an input gain so that the maximum level of the sound is not distorted. For example, in the example shown in FIG. 3, the sound level when the compressor 3 is started is, as shown in FIG. 2, 10 dB or more higher than the level during steady operation. Therefore, the digital signal processor, especially the A / D converter, needs to be able to process the start-up sound. However, if the start-up sound can be processed in this way, the A / A
The bit resolution of the D converter is worse than at startup. In order to obtain a noise reduction effect by active control, it is necessary to precisely match the phase and amplitude.However, if the bit length of the operation cannot be used effectively as described above, the quantization error due to the quantization error in A / D conversion Accuracy cannot be obtained due to the influence of quantization distortion and the error due to the finite word length of the quantization error due to rounding down of the calculation result in the calculation process, and the noise reduction effect is degraded. In particular, as shown in FIG. 2, a good noise reduction effect cannot be obtained when a sound source having a low level at normal times and a occasionally high level is targeted. Further, when the adaptive filter system is adopted, the input level is related to the adaptation speed, and when the level is low, the input level becomes slow, so that the obtained filter characteristic becomes inaccurate.

For this reason, in order to obtain a good silencing effect, it is necessary to always use the operation bits effectively, but there is a problem that this cannot be realized by the conventional device.

(Problems to be Solved by the Invention) As described above, in the conventional active silencer, there is a problem that sufficient accuracy cannot be obtained especially when the level of the detected sound is low, and good silencing characteristics cannot be exhibited. Was. Therefore, an object of the present invention is to provide an active silencer that always exhibits good silencing characteristics even when the level of a detected sound fluctuates.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides an electroacoustic transducer using a signal obtained by processing an acoustic signal detected by a sensor with a signal processing device. An active silencer in which a sound at a control target point is actively silenced by controlling an input side gain controller provided between a sensor and a signal processing device, a signal processing device and an electroacoustic transducer An output gain controller provided between
The gains of the input-side gain controller and the output-side gain controller are controlled so that the accuracy and resolution of the signal processing device are kept constant under the condition that the overall gain is kept constant corresponding to the input terminal signal level of the input-side gain control sensor. Gain control means.

(Operation) The gain control means monitors the input end signal level, and when the input signal level is low, increases the gain of the input side gain controller and decreases the gain of the output side gain controller instead. When the input signal level is high, the gain of the input-side gain controller is decreased, and instead, the gain of the output-side gain controller is increased. In this case, the gain control means controls the input-side gain controller so that the word length of the A / D converter located at the preceding stage in the signal processing device is always fully used (however, so as not to cause overflow or underflow). Control the gain.

(Example) Hereinafter, an example is described, referring to drawings.

FIG. 1 shows an active silencer according to an embodiment of the present invention.

In the figure, reference numeral 21 denotes a sensor for detecting a control target sound. The output signal of the sensor 21 is introduced to an input-side gain controller 22 composed of an electronic volume directly or via an amplifier (not shown). And
The signal that has passed through the input-side gain controller 22 is introduced into the signal processing device 23.

The signal processing device 23 is a digital signal processor, and includes an A / D converter 24 for converting a signal passed through the input-side gain controller 22 into a digital signal, and an A / D converter 24.
A digital filter 25 that filters the output of the digital filter to create a secondary additional sound signal required for silencing, and a D / A converter 2 that converts the output of the digital filter 25 to an analog signal
It is composed of six.

The output of the D / A converter 26 is provided to an electroacoustic transducer 28 for sound generation via an output-side gain controller 27 composed of an electronic volume.

On the other hand, a gain controller 29 for controlling the input side gain controller 22 and the output side gain controller 27 is provided. The gain controller 29 includes an input terminal signal of the input side gain controller 22, that is, a peak value detection circuit 30 for detecting a peak value of the input signal, and an average value detection circuit 31 for detecting an average value of the input signal. I have. Then, the output of the average value detection circuit 31 and the output of the peak value detection circuit 30 are introduced to the gain determination circuit 32. This gain judgment circuit
32 sets the input level of the A / D converter 24 based on both outputs,
Calculate the gain that can be used at the level used by using the entire word length without causing overflow or underflow. The output of the gain determination circuit 32 is provided on one side as a control signal of the input side gain controller 22, and the other side is provided as a control signal of the output side gain controller 27 via a reciprocal value calculation circuit 33. The reciprocal numerical operation circuit 33 is configured to output 1 / A when the output of the gain determination circuit 32 is A.

With such a configuration, the input-side gain controller
When the input signal level of 22 is low. The gain of the input-side gain controller 22 is increased, and the gain of the output-side gain controller 27 is reduced accordingly. When the input signal level is high, the input side gain controller 22
Is decreased, and the gain of the output side gain controller 27 is increased accordingly. The gain control is performed so that the word length of the A / D converter 24 always satisfies the condition of full use without causing overflow or underflow. Therefore, although the overall gain does not change, the signal level is adjusted so that the bit resolution of the A / D converter 24 is always maximized.In the end, without being influenced by the level of the input signal, Good silencing characteristics can always be exhibited.

[Effects of the Invention] As described above, according to the present invention, since the accuracy of the filter operation can be improved, it is possible to always exhibit good noise reduction characteristics without being affected by the level of the detected sound. .

[Brief description of the drawings]

FIG. 1 is a block diagram of an active silencer according to an embodiment of the present invention, FIG. 2 is a diagram for explaining a change in noise level of a compressor, and FIG. FIG. 6 is a diagram showing an example in which is muted. 21 ... Sensor, 22 ... Input gain controller, 23 ...
... Signal processing device, 24 ... A / D converter, 25 ... Digital filter, 26 ... D / A converter, 27 ... Output side gain controller, 28 ... Electroacoustic converter, 29 ... Gain control vessel.

Claims (1)

(57) [Claims] 1. An active silencer in which a sound at a control target point is actively silenced by controlling an electroacoustic transducer with a signal obtained by processing an acoustic signal detected by a sensor by a signal processing device. An input gain controller provided between the sensor and the signal processing device; an output gain controller provided between the signal processing device and the electroacoustic transducer; and the input gain. A gain for controlling the gain of the input-side gain controller and the gain of the output-side gain controller so as to keep the accuracy and resolution of the signal processing device constant under the condition that the overall gain is kept constant corresponding to the input terminal signal level of the controller. An active silencer comprising a control means.