When viewed as a waveform, slow-varying price trends constitute the waveform’s low frequency components and day-to-day fluctuations (noise) constitute the high frequency components. The objective in cycle analysis is to filter out the unwanted components – both low frequency trends and the high frequency noise – and retain only the range of frequencies over the desired swing period. A filter for doing this is called a Bandpass Filter and the range of frequencies passed is the filter’s bandwidth.
This is a companion discussion topic for the original entry at https://www.optuma.com/kb/optuma/tools/ehlers/bandpass-filter