# Order of filters

on the 24th page of this pdf file for Slaney's Gammatone filter bank this sentence is written:

The result is returned as an array of filter coefficients. Each row of the filter arrays contains the coefficients for four second order filters.

I am not really familiar with the concept of filters and I find it confusing searching it on the internet. does this sentence mean that the order of the filter is 8(4*2)? I would appreciate some easily explained references for this subject.

• no, that doesn't sound right. It's a bit hard to help you, because we don't know where exactly in the understanding of filters you are stuck. But you'll have to learn that - no way you understand the concept "filter bank" without understanding the concept "filter". Jun 4, 2020 at 21:09
• @MarcusMüller I do understand what filters are. but in this filterbank, each row, as I know, is a bandpass filter. my problem is the concept of orders of filters and that "what is a four second order filter". how can one filter, consist of four filters? (I know my questions are very basic and maybe even wrong but I don't know where to start.)
– Xgk
Jun 4, 2020 at 21:51
• "where to start": Signals and Systems textbook, learn what a filter is :) it really helps! Jun 5, 2020 at 8:42