Description

Spectral replacement filter reshapes the amplitude spectrum of each trace, keeping a chosen frequency band essentially unchanged while smoothly rolling off the amplitude outside it, instead of sharply zeroing it as a conventional bandpass filter would. Use it to attenuate low-frequency noise (such as ground roll or swell noise) and high-frequency noise while reducing the ringing artifacts that a hard-cutoff bandpass filter can introduce. The passband and the steepness of the roll-off on each side are fully independent, so the shaping can be made gentle or aggressive on either edge as needed.

Input data

Input gather

The seismic gather whose amplitude spectrum will be reshaped.

Parameters

Low Freq

Lower edge, in Hz, of the frequency band that is kept essentially unchanged. Frequencies below this value start to be reshaped according to the Low Roll-Off rate. Raise this value to more aggressively remove low-frequency noise such as ground roll or swell noise; lower it to retain more low-frequency signal.

Default: 8 Hz. Minimum: 0 Hz.

Low Roll-Off

Steepness of the amplitude roll-off below Low Freq, expressed as a slope in dB per octave. A value near 0 gives an abrupt, hard cutoff at Low Freq; a more negative value (for example -12 or -24) gives a steeper, more aggressive attenuation of low frequencies, while a smaller negative value gives a gentler transition with less risk of filter ringing.

Default: -6 dB/octave, a mild roll-off suitable for general-purpose noise attenuation with minimal ringing.

High Freq

Upper edge, in Hz, of the frequency band that is kept essentially unchanged. Frequencies above this value start to be reshaped according to the High Roll-Off rate. Lower this value to remove more high-frequency noise; raise it to preserve more high-frequency signal and resolution.

Default: 80 Hz. Minimum: 0 Hz.

High Roll-Off

Steepness of the amplitude roll-off above High Freq, expressed as a slope in dB per octave, using the same convention as Low Roll-Off. Make it more negative for a sharper high-cut; keep it small (close to the default) for a gentle, low-ringing roll-off.

Default: -6 dB/octave.

Output data

Output gather

The gather with a reshaped amplitude spectrum: frequencies between Low Freq and High Freq are preserved, and content beyond these edges is progressively rolled off rather than sharply removed, reducing filter-edge ringing compared with a conventional hard bandpass filter.

Difference gather

The difference between the input and output gathers, showing the energy removed or altered by the spectral reshaping. Use it to confirm that mainly unwanted low- and high-frequency content was affected, and that the target signal band was left intact.

References

Yilmaz, O., 1987, Seismic data processing: Society of Exploration Geophysicists.