High-Pass Filtering and the Nyquist Frequency

July 25, 2017 Andrew Jahn

Illustration of how sampling rate can generate a different waveform. Black: Original waveform; Red dots: Sampling of the original waveform. When a line (red) is interpolated among the sampled points of the original waveform, a waveform of a differen… — Illustration of how sampling rate can generate a different waveform. Black: Original waveform; Red dots: Sampling of the original waveform. When a line (red) is interpolated among the sampled points of the original waveform, a waveform of a different frequency is generated.

Note: See Wiktor's comment below for a comparison of frequency cutoffs across AFNI, FSL, and SPM.

Yesterday I had the following conversation on one of my YouTube videos:

J: Thanks for the video. My question pertains the cut-off filtering frequency: When you apply a HP [High-Pass] filter in fMRI (typically it's .008 Hz), is this at the Nyquist frequency? Meaning that .008/2 is the actual frequency we are removing? Thank you.