Hi, I was going through Tutorial 22: Source estimation and found this warning message.
Anyone can help me to answer what might be going on here and how I can address the issue?
The warning message came up after pressing Run for the low-pass 40 Hz process.
Thanks in advance.
Hi,
Digital filters have a transient (or settling) period in which, the filter reach their steady-state response. As such the filtered signal presents edge effects due to the filtering during the transient period. The warning is triggered as the transition period is longer than the 10% of the available data.
In the image below the first signal (green) is a 5-Hz sine wave + a 22-Hz cosine wave, and the red signal is the result of filtering the first signal with a low-pass filter with 10-Hz cut frequency. Note that the expected result is obtained after the transient period indicated on the top right corner of the plot.
The transition period depends on the filter order. Information on the transient period can be obtained before applying with the View filter response button in the filter process. In Brainstorm the duration of the transient period is calculated as the number of samples necessary for having 99% of the filter impulse response energy.
For additional information, go back to the advanced sections of tutorial 10:
https://neuroimage.usc.edu/brainstorm/Tutorials/ArtifactsFilter#What_filters_to_apply.3F
The messages you get are not errors but warnings, to inform you that there a large part of the filtered files may contain filtering artifacts.
