I am not sure what is going on. It appears that you are looking at a different data set from the one you posted earlier in this thread.
1. The low frequency peak is not the DC component. If you look closely at the graph, you can sse that the first point is at ~-78 while the peak is about -50. The peak appears to be at about 0.004 or 0.005 on the x-axis. That is in the range of 3-4 per minute if the x-axis is in hertz. That is a bit slow for respiratory modulation but certainly in the range where some physiological effects might be seen. The data set is rather small for getting meaningful measurements at frequencies that low.
2. The dataset you posted (100m.tdms) shows a wandering baseline with less than one complete cycle in the dataset. It does not appear to have the sample rate recorded, so it is hard to estimate the frequencies.
I suspect that what you are seeing is some "real" part of your signal. If yo do not want the low frequencies in your display, you can replace the first few bins in the spectral array with zeros.
Lynn
