JPH04355391A - Simulated-signal generating apparatus - Google Patents

Abstract

PURPOSE:To generate a wide-band acoustic signal having the specified frequency spectrum by less computing processes by repeatedly reading the time series data generated with an inverse Fourier transformation device, and multiplying the result by the white-noise analog signal from a white-noise generating circuit. CONSTITUTION:A frequency characteristic signal 11 is the signal for imparting the frequency spectrum of a wide-band acoustic signal to be simulated. The signal undergoes inverse Fourier transformation in an inverse Fourier transformation device l and becomes an inverse Fourier transformation output 12. A repeating reading circuit 2 stores the output 12 and repeatedly reads the outputs. The read output 13 is outputted. When the repeating period of the output 13 is made to be T, the frequency spectrum of the output 13 becomes the discrete spectrum level which is obtained by sampling the signal 11 at the interval of 1/T. Meanwhile, a narrow-band noise generating circuit 3 generates narrow-band noises 14. The noises 14 undergo A/D conversion with an analog/digital converter 4. In a multiplier 5, the output 13 and a digitized narrow-band noises 15 from the converter 4 are multiplied, and a digitized wide-band acoustic signal 16 is outputted. The signal 16 undergoes D/A conversion with a digital/analog converter 6, and a high-band acoustic signal 17 as the continuous spectrum is outputted.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention is utilized as a training device for improving the skill level of operators of passive sonar devices. In particular, the present invention relates to a passive sonar simulation signal generation device that simulates a broadband acoustic signal generated by an underwater target.

0002

2. Description of the Related Art As shown in FIG. 3, a conventional device generates a broadband acoustic signal whose spectral level can be arbitrarily determined. In FIG. 3, a frequency characteristic signal 11 is a signal giving a frequency spectrum of a broadband acoustic signal to be simulated, and is inverse Fourier transformed by an inverse Fourier transformer 1 to become an inverse Fourier transform output 12. The broadband noise generating circuit 7 outputs white noise 18, which is digitized by the analog-to-digital converter 4 into digitized white noise 19. The FIR filter 8 is an FIR filter that uses the inverse Fourier transform output 12 as a filter coefficient, and its frequency characteristics are equal to the characteristics given by the frequency characteristic signal 11. The digitized white noise 19 is filtered by the FIR filter 8 into a digitized broadband acoustic signal 16 and further analogized by the digital-to-analog converter 6 into a broadband acoustic signal 17. The broadband acoustic signal 17 is an output obtained by filtering white noise with a filter having characteristics equal to the frequency characteristic signal 11, and its spectrum is the same as that of the frequency characteristic signal 11.
be equivalent to.

0003

In such a conventional device, the calculation shown in the following equation is required using the FIR filter every time one sample of the digitized wideband signal is calculated.

mΣKi ・Nii=1Ki : Filter coefficient Ni : Sample value sequence of digitized white noise This formula shows that m multiplications and m additions are required to calculate one sample. . In order to increase the precision of the filter and provide accurate frequency characteristics, it is necessary to increase the order m of the filter, and therefore,
The conventional device has the disadvantage that the amount of calculation processing required to generate the simulated signal is large.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks, and to provide a simulated signal generating device that can generate a broadband acoustic signal having a desired frequency spectrum with a small amount of computational processing.

[0006]

[Means for Solving the Problems] The present invention provides an inverse Fourier transformer that generates time series data by inverse Fourier transforming frequency spectrum data of a broadband acoustic signal used in a passive sonar, and a white noise analog signal that generates a white noise analog signal. A noise generation circuit, an analog-to-digital converter for converting the white noise analog signal into a digital signal, and a digital signal output from the analog-to-digital converter to which the time-series data generated by the inverse Fourier transformer is applied to generate the broadband acoustic signal. In a simulated signal generation device comprising a signal processing circuit that generates a digital signal equivalent to the signal, and a digital-to-analog converter that converts the digital signal generated by the signal processing circuit into an analog signal, the white noise generation circuit is , the signal processing circuit is configured to generate a narrowband white noise analog signal, and the signal processing circuit repeatedly reads out the time series data generated by the inverse Fourier transformer and multiplies it by the narrowband white noise analog signal. It is characterized by

[0007]

[Operation] The spectrum of a desired broadband acoustic signal is converted into time-series data by an inverse Fourier transformer, and it is repeatedly read out by a repeat reading circuit. Since the time-series data read out in this manner has a discrete spectrum, it is multiplied by narrowband noise to create a continuous spectrum.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of this embodiment. As shown in FIG. 1, this embodiment includes an inverse Fourier transformer 1 that generates time series data by inverse Fourier transforming frequency spectrum data of a wideband acoustic signal used in a passive sonar, and a narrowband white noise analog signal. The narrowband noise generation circuit 3 that generates the narrowband white noise, the analog-to-digital converter 4 that converts this narrowband white noise analog signal into a digital signal, and the time series data generated by the inverse Fourier transformer 1 are repeatedly read out. A repeat reading circuit 2 and a multiplier 5, which are signal processing circuits that generate a digital signal equivalent to the broadband acoustic signal multiplied by a white noise analog signal, and a digital circuit that converts the digital signal generated by this signal processing circuit into an analog signal. and an analog converter 6.

Next, the operation of this embodiment will be explained. Figure 2
is an explanatory diagram for explaining the operation. The frequency characteristic signal 11 is a signal giving a frequency spectrum of a broadband acoustic signal to be simulated, and is inverse Fourier transformed by the inverse Fourier transformer 1 to become an inverse Fourier transform output 12. The repetitive readout circuit 2 stores the inverse Fourier transform output 12, repeatedly reads it out, and outputs it as a readout output 13. If the repetition period of the readout output 13 is T (seconds), the frequency spectrum of the readout output 13 is the frequency characteristic signal 11 divided by 1/T.
This results in discrete spectral levels sampled at intervals of (Hz). On the other hand, the narrowband noise generation circuit 3 generates narrowband noise 1
Generates 4. The narrowband noise 14 is digitized by the analog-to-digital converter 4 to produce digitized narrowband noise 1.
It becomes 5. Multiplier 5 multiplies readout output 13 and digitized narrowband noise 15 and outputs digitized wideband acoustic signal 16 . The digitized wideband acoustic signal 16 is converted to analog in an analog-to-digital converter 6 to become a wideband acoustic signal 17. The readout output 13 is modulated by a narrowband noise in a multiplier 5, and all of the discrete spectra at intervals of 1/T (Hz) have the shape of a spectral pattern of narrowband noise, and have a continuous spectrum approximately equal to the frequency characteristic signal 11. A wideband acoustic signal can be obtained.

0010

Effects of the Invention As explained above, the present invention replaces the FIR filter, which requires a large amount of calculation, with a repeat readout circuit and a multiplier, thereby eliminating the need for a large number of multiplications and additions to calculate one sample. This has the effect of dramatically reducing the amount of time required for multiplication.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram of each part showing the operation of the embodiment of the present invention.

FIG. 3 is a block configuration diagram showing the configuration of a conventional example.

[Explanation of symbols]

1 Inverse Fourier transformer 2 Repeated readout circuit 3 Narrowband noise generation circuit 4 Analog-digital converter 5 Multiplier 6 Digital to analog converter 7 Broadband noise generation circuit 8FIR filter 11 Frequency characteristic signal 12 Inverse Fourier transform output 13 Readout output 14 Narrowband noise 15 Digitized narrowband noise 16 Digitized wideband acoustic signal 17 Broadband acoustic signal 18 White noise 19 Digitized white noise

Claims (1)

[Claims] 1. An inverse Fourier transformer that generates time series data obtained by inverse Fourier transforming frequency spectrum data of a broadband acoustic signal used in a passive sonar, a white noise generation circuit that generates a white noise analog signal, and a white noise generation circuit that generates a white noise analog signal. An analog-to-digital converter that converts an analog signal into a digital signal, and a digital signal output from the analog-to-digital converter is subjected to time-series data generated by the inverse Fourier transformer to generate a digital signal equivalent to the broadband acoustic signal. In the simulated signal generation device, the white noise generation circuit includes a signal processing circuit that converts the digital signal generated by the signal processing circuit into an analog signal, and a digital-to-analog converter that converts the digital signal generated by the signal processing circuit into an analog signal. , and the signal processing circuit is configured to repeatedly read the time series data generated by the inverse Fourier transformer and multiply it by this narrowband white noise analog signal. .