I am curious about the necessity of demean/detrend before low/high pass filter.
I have seismic data which had been processed by cross correlation or other things. I want to use low pass filter for the processed data. For the raw seismic data, I know demean/detrend are needed before low-pass filter. But for the processed data which were going through demean/detrend during processing, is it still necessary to apply demean/detrend?