1D FFT Set Expansion Method

Use the 1D FFT > Advanced Settings > Set Expansion Method option (FFTSETEXTMD GX) to define how the padded (expanded) portion of the data is generated prior to performing a 1D FFT.

FFT Set Expansion Method dialog options

Expansion fill method

Specify how the padded data region is created. Available options: Maximum Entropy (default) Constrained LP Script Parameter: FFTEXTFILL.METHOD

Application Notes

Before performing an FFT, the data may be expanded (padded). This padded region is not filled with zeros; instead, it is predicted based on the existing data using one of two methods:

• Maximum Entropy Prediction (MEP)

• Constrained Linear Prediction (CLP)

These methods aim to preserve the spectral characteristics of the original signal while extending it.

Methods

Maximum Entropy Prediction (MEP)

This method determines the spectral content of the preceding real data segment and predicts a data function with the same spectral signature as the original data. As a result, the predicted data does not significantly alter the energy spectrum of the original signal.

Constrained Linear Prediction (CLP)

This method calculates a set of linear prediction coefficients from a real data segment and recursively extrapolates the data. Geophysical data, with its broad distribution characteristics, typically yields coefficients that produce reasonable extrapolations. However, if the data contains undamped oscillations (e.g., superimposed aircraft noise), CLP may become unstable. Applying an additional constraint during coefficient calculation ensures stability.

The detailed CLP methodology is beyond the scope of this topic. See the reference below for more information.

Reference