|
<< Click to Display Table of Contents >> Navigation: Filters > Band-pass filter (Distributed) |
This module applies a trapezoidal (four-corner) band-pass filter to seismic gathers, attenuating energy outside a defined frequency passband while preserving signal within it. The filter shape is defined by four frequency corners that create linear ramp zones between full rejection and full transmission, which avoids the ringing artefacts that can result from sharp-edged (brick-wall) filters.
Processing is performed in the frequency domain: each input trace is forward-transformed using a Fast Fourier Transform (FFT), the trapezoidal spectral filter is applied by multiplying the spectrum sample-by-sample, and the filtered trace is recovered by an inverse FFT. This approach is accurate and efficient for large datasets.
Note: This module is deprecated. For new workflows, use the standard Band-pass filter module instead, which provides equivalent functionality with active development and support.
The input seismic gather containing the traces to be filtered. Each trace in the gather is processed independently. The gather may be any type (common-shot, common-midpoint, common-offset, etc.). The sample interval of the input traces determines the Nyquist frequency limit of the filter, so the four frequency corner values must be set below the Nyquist frequency for the filter to operate correctly.
The filtered output gather. The output has the same geometry, sample interval, and trace count as the input. Frequency content outside the passband defined by the four corner frequencies has been suppressed. Amplitudes within the flat-top portion of the passband (between Frequency 2 and Frequency 3) are preserved at full strength.
The low-cut rejection frequency in Hz. Frequencies below this value are completely removed from the output. This is the lowest corner of the filter trapezoid, where the filter response is zero. The default value is 1 Hz. Set this value to suppress very-low-frequency noise such as ground roll or swell noise. It must be less than or equal to Frequency 2.
The low-cut pass frequency in Hz. This is the second corner of the filter trapezoid, where the filter ramps up from zero (at Frequency 1) to full transmission. Frequencies at and above this value, up to Frequency 3, pass through at full amplitude. The default value is 5 Hz. The range between Frequency 1 and Frequency 2 forms the low-frequency ramp (taper). It must be greater than or equal to Frequency 1 and less than or equal to Frequency 3.
The high-cut pass frequency in Hz. This is the third corner of the filter trapezoid, where full transmission ends and the filter begins to ramp down toward zero at Frequency 4. Frequencies between Frequency 2 and this value pass through at full amplitude. The default value is 200 Hz. Set this appropriately for the highest signal frequency in your data. It must be greater than or equal to Frequency 2 and less than or equal to Frequency 4.
The high-cut rejection frequency in Hz. Frequencies above this value are completely removed from the output. This is the highest corner of the filter trapezoid, where the filter response reaches zero. The default value is 210 Hz. The range between Frequency 3 and this value forms the high-frequency ramp (taper). Set this value to remove high-frequency noise while keeping a smooth spectral transition. It must be greater than or equal to Frequency 3, and should not exceed the Nyquist frequency of your data.