FIR Filter design, using different filter length than signal length
There's no requirement that the signal to be filtered has to have the same length as the filter - in fact, that's practically never the case.
So, there's no problem here; convolution doesn't need to &quot;define some padding&quot;; you'll find discrete convolution is just defined as finite sum over the available lengths.
The length difference between signal and filter isn't of relevance to &quot;track back&quot; a phenomen in the input signal: the time is always the time in the output signal, minus the filter's group delay. Assuming your filter is linear phase / time-symmetric, that's simply half the filter length.