Using Matlab poctave function under 3 Hz
poctave isn't a transform, it's a bank of filters.

I'm not sure why the artificial lower limit of 3 Hz exists.1 But you could try lying to it &mdash; tell it your sample rate is 160 Hz &times; 300 = 48 kHz, and then divide the frequency results by 300. That'll get you down to 0.01 Hz.



1 I can see that the limit of \$F_s\frac{3}{48000}\$ might be related to the maximum order of the filters used internally, but I don't see why there's an absolute limit of 3 Hz.