I have a question about the Delta in the Bandpass filter. What does it mean?
The Delta value (0..1) gives the width of the filter curve.
The Black Book says:
This bandpass filter has a center period of 30 bars and a width of 0.5 (the width determines the frequency range that can pass the filter).
But it's quite general definition and still it’s not clear…
I found John Ehlers' paper with a bandpass filter description: https://www.mesasoftware.com/papers/EmpiricalModeDecomposition.pdf
He writes the following about the bandpass filter with period 20 and delta=0.1:
The input variable delta is the approximate half-bandwidth of the filter. For the default settings with delta = 0.1, the filter will pass periods centered at 20 bars +/- 2 bars. In other words, the filter passes cycle components ranging between 18 and 22 bar periods while attenuating frequencies above and below this range.
Does Delta that is used in Zorro's BandPass have the same meaning? Is it a half-bandwidth of the filter? I think it will be useful to add this clarification to the manual if it's correct.
P.s. Ehlers' bandpass filter code in EasyLanguage can be found in the above-mentioned paper.