MATLAB: Delay when using lowpass(), medfilt1() and filter()

Question

Hello,

I'm trying to filter a data signal and I'm using y = lowpass(x,fpass,fs), medfilt(x),filter(b,a,x) for this.

I'm not sure if these functions in matlab introduce a delay to the signal or if they compensate themselves for this delay.

If they are how can I compensate for this delay?

Answer 1

The filter function introduces phase delay and phase dsitortion in the filtered signal. The filtfilt function does not, so it is best to use filtfilt for most signal processing applications.

The lowpass function (apparently) uses filtfilt rather than filter, because when I have used the second (optional) output of lowpass that returns a digital filter object, I get the same results as the lowpass function with filtfilt although not with filter.

The medfilt1 function does not mention how it filters the data, only that it ‘considers the signal to be 0 beyond the endpoints.’