The signal processing software that we use has inbuilt fast fourier transform (FFT) functions that deliver instant live analysis of what is being measured. Such tools when used with in-built filter functions provide an excellent live diagnostic tools that is useful for tracking measurements when conditions, such as speed, change.
In the same way that the software that we use for the data analysis has inbuilt FFT functions, also built into the software are frequency filter functions. These frequency filter functions are software code that can be set up to give either a low pass, high pass, or notch filters effect and may be used to screen the signal to allow only the frequencies that are of interest to pass for analysis and subsequent display.
We can choose from the following software filters when taking our measurements;
Low-pass filter – low frequencies are passed, high frequencies are attenuated.
High-pass filter – high frequencies are passed, low frequencies are attenuated.
Band-pass filter – only frequencies in a frequency band are passed.
Notch filter – rejects just one specific frequency - an extreme band-stop filter.
There are many other type of software filter available, but these represent the ones that we most commonly use.