  We study roughness probability distribution functions (PDFs) of the time
signal for a critical interface model, which is known to provide a good
description of Barkhausen noise in soft ferromagnets. Starting with time
``windows'' of data collection much larger than the system's internal ``loading
time'' (related to demagnetization effects), we show that the initial Gaussian
shape of the PDF evolves into a double-Gaussian structure as window width
decreases. We supply a physical explanation for such structure, which is
compatible with the observed numerical data. Connections to experiment are
suggested.
