Method and apparatus for digital time-variant filtering
AssigneeThe Standard Oil Company
InventorKenneth L. Peacock
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Abstract
A method and apparatus for digital time-variant filtering are disclosed. The digital time-variant filters are implemented using the Hilbert transform and a time-varying instantaneous frequency control function for controlling the cutoff frequency. The digital time-variant filters are adaptable to various filtering processes, that is, as either a high-cut, low-cut, band-pass, or reject filter. The various digital time-variant filters are stable in that no unusual transients occur in the output signal; are flexible in that the cutoff frequency is controlled by a selectable time-varying control function signal; and are efficient in that computational requirements are only twice to 16 times that of known digital time-invariant filters.
Claims15
A method for processing a digital electrical signal having a time-varying character, comprising the steps of:
- selecting a digital time-varying control function signal for controlling cutoff frequency;
- discretely integrating the selected control function signal;
- combining the electrical signal with the integrated control function signal;
- applying a Hilbert transform operator to the combined electrical signal and integrated control function signal;
- and
- extracting a time-variant filtered electrical signal from the combined electrical signal and integrated control function signal to which the operator has been applied;
- wherein the Hilbert transform operator is determined by:
- selecting a roll-off interval for time-variant filtering;
- selecting an attenuation value for time-variant filtering;
- determining a Hilbert transform stength of weighting based on the selected attenuation value;
- determining a Hilbert transform operator length based on the selected roll-off interval and the attenuation value;
- and
- determining the Hilbert transform operator based on the strength of weighting and the operator length.
A method for processing digitized seismic information, comprising the steps of:
- determining a Hilbert transform operator;
- selecting a digital time-varying control function signal for controlling cutoff frequency;
- discretely integrating the selected control function signal;
- combining the digitized seismic information with the integrated control function signal;
- applying the Hilbert transform operator to the combined digitized seismic information and integrated control function signal;
- and
- extracting time-variant filtered digitized seismic information from the combined digitized seismic information and integrated control function signal to which the operator has been applied.
An apparatus for processing a digital electrical signal having a time-variant character, comprising:
- means for inputting a selected digital time-variant control function signal for controlling the cut-off frequency of the electrical signal;
- means for discretely integrating the selected control function signal;
- means for combining the electrical signal with the integrated control function signal;
- means for applying a Hilbert tranform operator to the combined electrical signal and integrated control function signal, wherein the means for applying the Hilbert transform operator includes means for determining the Hilbert transform operator for controlling roll-off interval and attenuation, comprising:
- means for inputting selected Hilbert transform strength of weighting;
- means for inputting selected Hilbert transform operator length;
- and
- means for determining the Hilbert transform operator for the strength of weighting and the operator length inputs;
- and
- means for extracting a time-variant filtered electrical signal from the Hilbert tranformed combined electrical signal and integrated control function signal.
Dependencies are inferred from the claim text.