Abstract:
It is possible to easily design an FIR filter having an arbitrary frequency characteristic only by inputting a waveform of a desired frequency characteristic as an image without having any special knowledge, i.e., by inputting a waveform of a desired frequency characteristic as a numerical value series and performing reverse FFT of this to obtain a filter coefficient group. Moreover, by performing a special rounding calculation to the numerical value series obtained by the reverse FFT, it is possible to simplify the filter coefficient value without lowering the filter characteristic accuracy and significantly reduce the number of times a multiplier as a filter constituting element is used. Furthermore, by performing window multiplication to the result of the reverse FFT, it is possible to increase the length of the numerical value series input firstly so as to minimize the frequency error and minimize the number of filter coefficients, thereby simplifying the configuration of the digital filter to be designed.
Abstract:
A filter circuit is composed of FIR filters, and the filter factor is of a symmetrical type, thereby realizing a linear phase characteristic and preventing phase distortion even if a desired frequency band is emphasized. The first filter factors of a low-pass filter are determined so that the first filter factors may be the terms of a sequence in which the sum of the terms is not zero, the sign of the sum of every other terms is the same as that of the other every other terms, and the sum of the every other terms is equal to that of the other every other terms. Thus, by only changing a part of the signs of the filter factors, second filter factors of a high-pass filter can be simply determined so that they may be the terms of a sequence in which the sum of the terms is zero, the sign of the sum of every other terms is opposite to that of the other every other terms, and the absolute value of the sum of the every other terms is equal to that of the other every other terms.
Abstract:
For data to be compressed and having periodicity, two windows of identical size are set for two intervals in accordance with peaks appearing almost periodically and sample data is alternately rearranged between the windows of the identical size, thereby replacing the frequency of data having periodicity with approximately a half frequency without deteriorating reproducibility into original data, so that the replaced data of a low frequency is subjected to compression. This rearrangement processing may be applied to a compression having a characteristic that the compression ratio cannot be increased in a high frequency region, so as to increase the compression ratio without deteriorating the quality of the reproduced data obtained by decompression.