Filter adaptive frequency resolution
AssigneeTelefonaktiebolaget L M Ericsson (publ)
InventorsAnisse Taleb, Harald Pobloth, Erlendur Karlsson, Erik Norvell
Life of this patent
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Abstract
In signal processing using digital filtering the representation of a filter is adapted depending on the filter characteristics If e.g. a digital filter is represented by filter coefficients for transform bands Nos. 0, 1, . . . , K in the frequency domain, a reduced digital filter having coefficients for combined transform bands, i.e. subsets of the transformed bands, Nos. 0, 1, . . . , L, is formed and only these coefficients are stored. When the actual filtering in the digital filter is to be performed, an actual digital filter is obtained by expanding the coefficients of the reduced digital filter according to a mapping table and then used instead of the original digital filter.
Claims22
A method of processing an input signal including the successive steps of:
- providing the input signal to a digital filter represented by a set of filter coefficients, and
- filtering the input signal by the digital filter, wherein, before the step of filtering, said filter coefficients are expanded from a reduced digital filter represented by and stored as reduced filter coefficients and corresponding to an original digital filter, at least one of the reduced filter coefficients corresponding to or substantially agreeing with two of the filter coefficients in the original digital filter, the reduced digital filter obtained by the steps of:
- comparing the filter coefficients of the original digital filter to each other,
- combining, according to the result of the comparing, filter coefficients that are equal to each other or are sufficiently close to each other, to subsets of filter coefficients, each such subset represented by a reduced filter coefficient obtained from the filter coefficients in the subset.
A device for processing an input signal including:
- a memory place for storing reduced filter coefficients of a reduced digital filter,
- a memory place for storing a table mapping the reduced filter coefficients to filter coefficients of an original digital filter,
- logical unit for expanding the reduced filter coefficients to form actual filter coefficients that are equal to or substantially agrees with the filter coefficients of the original digital filter, and
- a filtering unit for filtering the input signal using the actual filter coefficients.
A method of processing an input time domain signal including the successive steps of:
- transforming the input signal to the frequency time to give a transformed input signal, and
- filtering in a filter the transformed input signal by multiplying the amplitudes of frequency components in the transformed signal by coefficients of the frequency-domain impulse response of the filter, wherein the coefficients are derived from a reduced set of coefficients, at least one of the coefficients in the reduced set representing the filter response in a frequency band covering at least two adjacent frequencies used in the transforming.
A method of storing filter coefficients representing an original digital filter represented by original filter coefficients including the successive steps of:
- comparing the original filter coefficients to each other,
- combining, according to the result of the comparing, filter coefficients that are equal to each other or are sufficiently close to each other, to subsets of filter coefficients, each such subset represented by a reduced filter coefficient obtained from the filter coefficients in the subset, and
- storing the reduced filter coefficients and a table mapping the subsets to the original filter coefficients.
Dependencies are inferred from the claim text.