Perfect, thank you for the answer. Usually, I use epochs of the same length. This time I wanted to select portions of the signals clean from artifacts, despite their temporal lengths. If I do not concatenate them, Brainstorm shows the temporal length of the #1 segment as automatic option when estimating the data covariance (for both Baseline and Data). Whereas with the concatenated epochs, it will show the total duration of the concatenated file in the Baseline and Data input.