If you pick pl=2 and pu = 4 and your data is daily, then indeed you filter out the trend that has frequency up to 4 days. So, your trend line is a sum of trigonometric functions with the aforementioned periodicity. The cycle comprises all the other remaining frequences.
In excel use the LN function to perform the log. The difference in logs should be done with the log of the most recent value minus the log of the past value
LN(Present) -LN(PAST) = Growth%
Take the excel handle and pull it down so that you can copy fill the formula to do all the
At this point you may also want to chose which decimal ...