Downsampling and aliasing effect in python st.resample

Question

Does downsampling using stream.resample () in Python introduce aliasing effect? I want to investigate a signal below 4 Hz. It has the original sampling rate of 100 Hz but I need to downsample it as much as possible. If I use In Python st.resample() based on the documentation (https://docs.obspy.org/packages/autogen/obspy.core.stream.Stream.resample.html) it does the resampling using a Fourier method. If I downsample to 8 Hz:

st.resample (8)

• Will I have an aliasing effect considering that my interest frequency is below 4 Hz?

• What if I set the no_filter to False:

  st.resample (8, no_filter=False)

Answer 1

1. no aliasing will happen as this truncates and interpolates points in the frequency domain.
2. using no_filter=False only reduces high frequency components, which only smooth the signal, it doesn't matter in terms of aliasing, you can think of it as smoothing after the resampling.