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The Notch ext module removes narrowband coherent noise at one or more specific frequencies from seismic data. It is designed to suppress tonal interference sources such as powerline hum (50 or 60 Hz), cable vibrations, or acquisition instrument artifacts that appear as spectral spikes in the data. Unlike a conventional band-reject filter that applies a fixed notch shape, this module allows you to define multiple independent notch bands in a single pass, each with its own center frequency and bandwidth.
The filter operates by isolating the target frequency band using a Butterworth bandpass filter and then subtracting it from the original trace, effectively creating a bandstop (notch) response. For each notch entry you provide, the center frequency and half-bandwidth define the edges of the rejected band as (center - deviation) to (center + deviation) Hz. The filter can be applied in zero-phase mode (default, no phase distortion) or minimum-phase mode. Multiple notch entries are processed sequentially, so harmonic series — for example 50, 100, and 150 Hz — can be suppressed simultaneously by adding three entries to the Frequencies list.
The seismic dataset to process. This item carries the data source connection, sampling parameters, and trace header information that the module uses to correctly apply the filter.
The seismic gather (a group of traces) delivered to the module for processing. Each trace in the gather is filtered independently. Only live traces (trace identification header = 1) are processed; auxiliary or dead traces pass through unchanged.
This parameter group contains the global filter settings that apply to all notch bands defined in the Frequencies list.
Controls the steepness of the Butterworth filter rolloff at the edges of each notch band. A higher order produces a sharper transition from the pass band into the rejected band, giving a more precise notch shape that removes less of the surrounding signal. A lower order produces a gentler rolloff and removes a slightly broader range of frequencies. The default value is 5, which provides a good balance between notch sharpness and numerical stability. For very narrow notch bandwidths (small deviation), consider increasing the order to 7 or higher to ensure complete suppression of the target frequency. Minimum allowed value is 1.
Selects the phase characteristic of the notch filter. When set to false (the default), the filter is applied in zero-phase mode by filtering the trace in the forward direction and then repeating the pass in the reverse direction. This preserves wavelet symmetry and introduces no phase shift, which is the recommended setting for most processing workflows including NMO, migration, and AVO analysis. When set to true, only a single forward pass is applied, resulting in a minimum-phase response. Use minimum-phase mode only when the downstream process specifically requires causal filtering, or when matching the filter response to a minimum-phase wavelet convention.
A list of one or more notch band definitions. Each entry in the list specifies a frequency to suppress and the half-width of the rejection band around it. At least one entry is required. Add additional entries to suppress harmonic series or multiple independent noise sources in a single processing step. The module processes each entry sequentially, applying successive notch operations to the gather.
Dominant frequency — The center frequency (in Hz) of the notch band to suppress. This should be set to the exact frequency of the noise source as identified from a frequency spectrum analysis. Valid range is 0.001 to 32000 Hz. The default value is 50 Hz, which corresponds to powerline interference common in European and Asian acquisition environments (use 60 Hz for North American data).
Max deviation — The half-bandwidth (in Hz) of the notch, measured from the center frequency. The filter will reject the frequency range from (Dominant frequency - Max deviation) to (Dominant frequency + Max deviation). For example, with a dominant frequency of 50 Hz and a max deviation of 5 Hz, the rejected band spans 45 to 55 Hz. Use a smaller deviation to preserve more of the signal spectrum close to the target frequency; use a larger deviation if the noise has slight frequency variability or if the spectral spike is broad. The default value is 5 Hz. Valid range is greater than 0.0000001 Hz up to 32000 Hz.