JPH02154161A - Method and device for frequency analysis - Google Patents

Abstract

PURPOSE:To correctly display a power spectrum by setting a band so that a peak frequency of the power spectrum resulted from a narrow band frequency analysis is not overlapped with frequencies of the upper and lower limits of the band width on a wide band frequency analysis. CONSTITUTION:The acoustic pressure of a sound source 10 is detected by a microphone 12, amplified by an amplifier 14 and stored in memory means 16. Then, data of the means 16 are analyzed for narrow band frequencies in analysis means 18. By means of using the above result, the frequency fm, the spectrum power of which is made to be maximum, is obtained in frequency components detecting means 20. This frequency fm is inputted to band decision means 22, wherein a center frequency of the band is moved so that the frequency fm is made to be the center frequency fi of a certain band in the manner of not coinciding with the frequencies fT, fB of the upper and lower limits of each bandwidth, then new band is set. Further, the spectrum power in the band width newly obtained is calculated in wide band frequency analysis means 24, and the result is displayed on display means 26.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a frequency analysis method and apparatus used for evaluating noise, vibration, etc.

(Background of the Invention) Frequency analysis of input waveforms such as pressure, velocity, acceleration, displacement, distortion, etc. indicating noise, vibration, etc. is widely performed to evaluate these input waveforms.

In this analysis method, first the entire frequency range of the input waveform is
FFT by dividing into 24 equal parts, 512 equal parts, etc.
Find the frequency spectrum of (fast Fourier transform).

Then, the spectral power of each frequency component in this narrow band, that is, the square of the absolute value of the frequency component, is determined to obtain a narrow band power spectrum (referred to as narrow band frequency analysis). However, if the frequency axis of this narrowband power spectrum is linear and the spectrum is displayed over a wide frequency range, it is inappropriate to understand the spectral structure of the low frequency part, and it has a poor relationship with the sense of hearing. Problems arise, such as the inability to compare spectra using techniques such as 1/3 octave and 1 octave analysis, which have been widely used in the past.

Therefore, a method has been used in which the frequency axis is also on a logarithmic scale and a spectrum display is obtained every 1/3.1 octave (constant percentage (ratio) bandwidth analysis).

In the conventional wideband frequency analysis using this constant ratio bandwidth, the center frequency of each band was determined according to a predetermined standard. This is 2° for 1 octave band and 2° for 1/3 octave band based on LkHz.
The center frequency of each band is determined by the relationship.

However, in this case, the peaks of the frequency power spectrum of the input waveform may overlap the boundaries of the bandwidths, and in this case, there is a problem that the power spectrum appears to be small.

FIG. 2.3 is a diagram showing this situation, and in FIG. 2, the spectrum a of the input waveform has a bandwidth. FIG. 3 shows the case where the spectrum a falls between the upper and lower limit frequencies of i/), and the case where the spectrum a falls between the boundaries of the band widths bo and b+, respectively.

Here, spectrum A in FIG. 2, which is the result of wideband frequency analysis of constant ratio bandwidth, is equal to the area of spectrum a of narrowband analysis, and spectrum A1 . The total area of A, is equal to the area of spectrum a, so spectrum A1 in FIG. A 2 becomes half of the spectrum A in FIG. 2, causing the inconvenience that it appears less clearly.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and is intended to prevent the spectrum of the analysis result from appearing apparently small due to the spectrum of the human waveform entering the band boundary of wideband frequency analysis. The purpose of this invention is to provide a frequency analysis method that does the following.

A second object of the present invention is to provide an apparatus that can be used directly for carrying out this method.

(Structure of the Invention) According to the present invention, the first object is to provide a frequency analysis method for further wideband frequency analysis of the narrowband frequency analysis result obtained by fast Fourier transform. This is achieved by a frequency analysis method characterized in that the band is set so that the peak frequency does not overlap the upper and lower limit frequencies of the bandwidth of the wideband frequency analysis.

Here, the frequency of the largest peak among the peaks of the power spectrum of the input waveform may be set so that it does not overlap with the upper and lower limit frequencies of the band width, or the frequency of these peaks of the spectrum may be set to be the center frequency of the band. .

A second object of the present invention is to provide a memory means for storing sample values of an input waveform, a narrowband frequency analysis means for fast Fourier transforming the input waveform using the sample value to obtain a narrowband frequency power spectrum, and a narrowband frequency analysis means for obtaining a narrowband frequency power spectrum. a frequency component detection means for determining the frequency at which the power spectrum peaks; a band determining means for determining a band for broadband frequency analysis so that the frequency at which the power spectrum peaks does not overlap with the upper and lower limit frequencies of the bandwidth; This is achieved by a frequency analysis device characterized in that it includes a broadband frequency analysis means for determining a power spectrum according to the band.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention. This embodiment analyzes noise from a sound source 10 such as a motorcycle. The sound pressure of the sound source 10 is detected by the microphone 12, and the analog signal output from the microphone 12 is sent to the amplifier 14.
The input waveform i is amplified by the input waveform i. This input waveform i is A/
The data is D-converted, that is, quantized at predetermined sampling intervals, and stored in the memory means 16. For example, 512 (8 bits) or 1024 (16 bits) sampling values can be stored.

18 is a narrowband frequency analysis means, which is composed of an FFT (fast Fourier transform) device. FF of this analysis means 18
At T, a discrete Fourier transform is calculated, but distortion occurs when the period of the input waveform i is not an integral multiple of the number of samples N. Therefore, it is of course possible to cut out the waveform by applying a time window, or to use a weight function such as a panning window to eliminate discontinuity between the beginning and end of the time window.

This analysis means 18 performs narrowband frequency analysis by FFT calculation, and using the result, the frequency component detection means 20 determines 1 at the next frequency where the spectral power becomes maximum. This frequency f is input to the band determining means 22. This means 22 has an upper and lower limit frequency ft for each band width.
, f-, for example, the band center frequency is shifted so that this frequency f, , becomes the center frequency f of a certain band, and a new bandwidth is set. For example, in the case of 1 occube band for this center frequency f, 2
The center frequency fln of a different band is determined every n octaves, or every 2n/3 octaves in the case of a 1/3 octave band, and the upper limit frequency fT of each band at this time
In the case of a 1-octave band, the lower limit frequency fs is: fT=21/2 ・fln iI B= 2-1/2・f I+'11/3 In the case of an octave band, f1=2176 ・f.

t, +=2-'''·f.The broadband frequency analysis means 24 calculates the spectral power that falls within this newly found bandwidth, and displays it on the display means 26 such as a CRT. The means 26 performs frequency correction corresponding to hearing (for example, J
Of course, the frequency correction characteristic A) defined in IS C1502, 1505, etc. may be used.

In this embodiment, the band determining means 22 determines the band so that the maximum frequency component obtained by the frequency component detecting means 20 becomes the center frequency Rt of the band. The center frequency may be determined by selecting a peak so that the peak does not fall on the boundary between bands, or the center frequency may be determined manually.

(Effects of the Invention) As described above, the first invention of the present invention examines the peak of the power spectrum from the results of narrowband frequency analysis, and determines the band so that the frequency of this peak does not fall within the upper and lower limit frequencies of the band. Since the wideband frequency analysis is performed using the method, there is no problem that the peak of the power spectrum falls on the boundary between bands and the result of the wideband instrument frequency analysis appears smaller than it appears.

Further, according to the second invention, it is possible to obtain a frequency analyzer that can be used directly to implement the method of the first invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIGS. 2 and 3 are diagrams for explaining the reason why the power spectrum appears small in appearance. 16... Memory means, 18... Narrowband frequency analysis means, 20... Frequency component detection means, 22... Band determination means, 24... Wideband frequency analysis means, 26... Display means. Patent applicant Yamaha Motor Co., Ltd.

Claims (6)

[Claims] (1) In a frequency analysis method in which narrowband frequency analysis results obtained by fast Fourier transform are further subjected to wideband frequency analysis, the peak frequency of the power spectrum of the narrowband frequency analysis result is above the bandwidth of the wideband frequency analysis. - A frequency analysis method characterized by setting bands so that they do not overlap the lower limit frequency. (2) The frequency analysis method according to claim (1), wherein the band is set so that the maximum frequency of the power spectrum of the input waveform does not overlap with the upper and lower limit frequencies of the bandwidth of the wideband frequency analysis. A frequency analysis method characterized by: (3) The frequency analysis method according to claim (1) or (2), wherein the band is determined so that the peak frequency of the power spectrum becomes the center frequency of the bandwidth. (4) memory means for storing sample values of the input waveform;
narrowband frequency analysis means for performing fast Fourier transform on the input waveform using the sample values to obtain a narrowband frequency power spectrum; frequency component detection means for determining frequencies at which the power spectrum peaks; a band determining means for determining a band for wideband frequency analysis so that the frequency does not overlap the upper and lower limit frequencies of the bandwidth; and a wideband frequency analysis means for determining a power spectrum according to the determined band. Analysis equipment. (5) The frequency analysis device according to claim 4, wherein the band determining means determines the band such that the frequency at which the narrowband power spectrum is maximum becomes the center frequency of the band for wideband frequency analysis. . (6) Claim (4) wherein the band determining means is capable of manually setting the center frequency and upper and lower limit frequencies of the band.
) or the frequency analyzer according to (5).