JPH0357924A - Method and apparatus for measuring transmission function for acoustic system - Google Patents

Abstract

PURPOSE:To enable the outputting of a signal component with a better S/N ratio by detecting a frequency component with a higher correlation in transmission function between a sound source and a sound receiver to make an interpolation between frequency components high in correlation detected. CONSTITUTION:A measuring device is made up of two microphones 2a and 2b to detect sounds generated from a rotary machine 1 such as compressor as sound source, a frequency analyzer 3, a rotation synchronous component detector 4 as a frequency component detector, an interpolator 5, a transmission function resynthesizer 6 and an arithmetic device 7. Then, as it is difficult to extract a frequency component with a higher correlation only from results of measurement obtained with the analyzer 3, a frequency component with a higher correlation is detected with a detector 4 based ona signal outputted from the analyzer 3. After the detection of the frequency component with a higher correlation with the detector 4, a linear interpolation is made between adjacent frequency components higher in correlation with an interpolator 5. The frequency component interpolated linearly with the interpolator 5 is synthe sized with a resynthesizer 6 to be outputted as transmission function.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method and apparatus for measuring a transfer function of an acoustic system formed by a sound source and a space.

(Prior Art) Conventionally, when measuring the transfer function of an acoustic system formed by a sound source and a space, two sound receivers are placed in front of a speaker 10, which is a sound source, as shown in FIG. Microphones lla and llb are arranged at a predetermined interval, a signal S with clear frequency characteristics is input from a signal generator (not shown) to the speaker 10, and the speaker 10 and the microphones lla and llb are connected.
Transfer functions L, , L2 between microphones 1l and 1l
a, llb were converted into electrical signals M, , M2.

The signal M. which is converted by the microphone lla. is the frequency f
Then, M+ (f)-S (f) ◆L+ (f)...
・(1), and the signal M2 similarly converted by microphone llb is M2 (f)-S (f) ・L2 (f)...
・(2) becomes. Furthermore, this t, + (f), L2
(f) includes the characteristics of the speaker 10.

By the way, in the above case, a speaker was used as the sound source, but in an actual acoustic system, a rotating machine such as a compressor or blower that generates noise is used as the sound source.
A signal component corresponding to the signal S with clear frequency characteristics output from the signal generator (not shown) described above cannot be extracted. Therefore, as shown in equation (3) below, equation (1) can be changed to (
2) Eliminate the term S by dividing by the equation, and calculate the sound source (rotating machine) and microphone lla, 11. It is represented by the transfer characteristic LIL2 between b.

That is, when the rotating machine is operated, the microphones 11a,
The signals Ml and M2 converted by llb may be divided by each other.

However, since the result obtained by equation (3) uses a rotating machine that generates noise, the frequency components with high correlation among the signal components between the sound source (rotating machine) and each microphone lla, llb are not reliable. However, in the uncorrelated part, only a very poor signal-to-noise ratio can be obtained. For example, as shown in the coherence function shown in FIG. 4, the sound generated by a compressor has a high correlation at the rotational frequency, the power supply frequency, and its harmonics, but other frequency components have almost no correlation. When such a coherence function is used to perform addition, subtraction, multiplication, division, etc., there are overwhelmingly many uncorrelated components, so only a so-called noisy transfer function with very fine fluctuations is obtained (fifth (See Figures (a) and (b)). Note that FIG. 5(a) shows the amplitude in the frequency domain, and FIG. 5(b) shows the phase (arctanzent).

Therefore, if the transfer function obtained in this way is inversely Fourier transformed back to a time domain signal, the true signal will be completely buried in noise, and only signal components with a poor S/N ratio will be output. Ta.

(Problem to be Solved by the Invention) As mentioned above, conventionally, when measuring the transfer function of a space in which a rotating machine such as a compressor that generates sound (noise) is installed, the output signal component is S/N. Because of the poor ratio, it was not possible to obtain highly reliable results even if calculations were performed using this output signal, for example.

The present invention was made for the purpose of solving the above-mentioned problems, and the S/N
The present invention aims to provide a method and apparatus for determining the transfer function of an acoustic system that can output signal components with a good ratio.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the problems described above, the present invention provides a method for measuring the transfer function of an acoustic system formed by a sound source and a space, in which at least two or more sound receivers It is characterized in that it captures sound generated from a sound source, detects frequency components with a high correlation between the sound source and a sound receiver, and interpolates between the detected frequency components with a high correlation.

Further, the measuring device according to the present invention includes at least two or more sound receivers that take in sound generated from a sound source, and measures a transfer function between the sound receivers based on a signal input from the sound receivers. A frequency analyzer, a frequency component detector that detects highly correlated frequency components based on a signal input from the frequency analyzer, and interpolation that interpolates between the highly correlated frequency components detected by the frequency component detector. and a transfer function recombiner that resynthesizes the frequency components interpolated by the interpolator into a transfer function.

(Operation) According to the present invention, by detecting frequency components with high correlation in the transfer function between the sound source and the sound receiver and interpolating between the detected frequency components with high correlation, small fluctuations are eliminated and S A signal component with a good /N ratio is output.

(Example) Hereinafter, the present invention will be described in detail based on one embodiment shown in the drawings.

FIG. 1 is a block diagram showing a transfer function determining device according to the present invention. As shown in this figure, the transfer function measuring device according to the present invention includes two microphones 2a that detect sound (operating sound) generated from a rotating machine 1 such as a compressor, which is a sound source.
, 2bs frequency analyzer 3, a rotation synchronization component detector 4 as a frequency component detector, an interpolator 5, a transfer function resynthesizer 6, and an arithmetic unit 7.

The two microphones 2a and 2b, which are sound receivers, are placed at predetermined positions in the space where the rotary machine 1 is installed, and convert the sound generated from the rotary machine 1 into electrical signals. The output signal is input to the frequency analyzer 3. The frequency analyzer 3 selects the microphones 2a, 2a and 2a based on the input signal.
2b (see Figures 5(a) and (b)). The sound generated from the rotating machine 1 is mainly composed of rotational sound and electromagnetic sound, so the rotational sound consists of its fundamental frequency and its harmonics, and the electromagnetic sound consists of components twice the fundamental frequency of the power supply. The fundamental wave, the 1-fold wave, is dominant.

Then, the result obtained by the frequency analyzer 3 (Fig. 5 (
a). Since it is difficult to extract frequency components with high correlation using only the method (see (b)), the frequency components with high correlation are detected by the rotational quarter component detector 4 based on the signal input from the frequency analyzer 3. When detecting highly correlated frequency components with the rotation synchronization component detector 4, the microphones 2a,
The coherence function between 2b is used for evaluation (see Figure 4). At this time, all frequency components whose coherence function value is, for example, 09 or more are extracted and stored as a frequency table, and the value of the transfer function is also stored in the table. As a result, it is possible to extract highly correlated high-frequency components other than rotational sound and electromagnetic sound among sounds generated from the rotating machine 1, such as noise generated by resonance and highly correlated noise intensity generated by modulation.

After the rotation synchronization component detector 4 detects frequency components with high correlation, the interpolator 5 linearly interpolates between adjacent frequency components with high correlation. The frequency components linearly interpolated by the interpolator 5 are combined by the transfer function resynthesizer 6, and the frequency components are combined by the transfer function resynthesizer 6.
) and (b). Figure 2(a) shows the amplitude in the frequency domain,
FIG. 2(b) shows the phase (arctangent). In this way, by selecting only correlated frequency components, performing linear interpolation between adjacent frequency components, and then synthesizing the transfer function in the transfer function resynthesizer 6, an S/ A signal component with a good N ratio can be obtained.

Then, the transfer function with a good S/N ratio obtained by the transfer function resynthesizer 6 is inversely Fourier-transformed by the arithmetic unit 7 and returned to a time domain signal to obtain an impulse response. real-time signal processing using
For example, when applied to active silencing control, good silencing control can be performed.

In addition, in the above embodiment, linear interpolation was performed between adjacent frequency components with high correlation, but as shown in FIG. Signal component (b+t)2+ b. ,,b4,b5
) may be interpolated by connecting them with a curve that passes through the average value.

That is, the curve connecting al and a2 is al and bl b+
and b2 , b2 and b3 , b3 and b4 , b4 and b5
, b5 and a2, respectively.

〔Effect of the invention〕

As described above in detail based on the embodiments, according to the present invention, by extracting only highly correlated components and interpolating between the highly correlated components, a transfer function with a good S/N ratio can be obtained. can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a device for determining the transfer function δp1 of an acoustic system according to the present invention, and Figs. 2 (a) and (b) show linear interpolation using an interpolator and synthesis using a transfer function recombiner. FIG. 3 is an explanatory diagram showing an interpolation method according to another embodiment of the present invention, FIG. 4 is a diagram showing an example of a coherence function, and FIGS. 5(a) and (b) ) are diagrams showing transfer functions measured by a frequency analyzer, respectively, and FIG. 6 is a diagram showing the configuration of a conventional transfer function measuring device. 1... Rotating machine 2a, 2b... Microphone 3... Frequency analyzer 4... Rotation synchronous component detector (frequency component detector) 5...
...Interpolator 6...Transfer function resynthesizer 7...Arithmetic unit υ, patent attorney Hidekazu Miyoshi Figure 1

Claims (3)

[Claims] (1) In a method for measuring the transfer function of an acoustic system formed by a sound source and a space, at least two or more sound receivers capture the sound generated from the sound source, and the correlation between the sound source and the sound receiver is determined. A method for measuring a transfer function of an acoustic system, characterized by detecting a high frequency component of and interpolating between the detected frequency components with high correlation. (2) The method for measuring a transfer function of an acoustic system according to claim 1, wherein the interpolation section is determined to pass through an average value of frequency components with little correlation existing between correlated frequency components. . (3) at least two or more sound receivers that capture sound generated from a sound source; a frequency analyzer that measures a transfer function between the sound receivers based on a signal input from the sound receiver; a frequency component detector that detects highly correlated frequency components based on a signal input from an analyzer; an interpolator that interpolates between the highly correlated frequency components detected by the frequency component detector; 1. A transfer function measurement device for an acoustic system, comprising a transfer function resynthesizer that resynthesizes interpolated frequency components into a transfer function.