Band pass filtering not working at lower values

usgs / swarm

a Java application designed to display and analyze seismic waveforms in real-time.

http://volcanoes.usgs.gov/software/swarm

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Band pass filtering not working at lower values #102

Closed dlnorgaard closed 7 years ago

dlnorgaard commented 7 years ago

Javier Pacheco reports problem filtering between 0.0125 and 0.1. Confirmed by Jeremy. Works at higher at higher values. Seems to go back to at least 2.6.2.

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dlnorgaard commented 7 years ago

Similar results obtained from Matlab. Maybe a non-issue?

tparker-usgs commented 7 years ago

Matt suggests using a low-order filter with zero phase shift. This seems to produce reasonable results, but I haven't validated it.