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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.

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  • $\begingroup$ 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". $\endgroup$ Jun 4, 2020 at 21:09
  • $\begingroup$ @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.) $\endgroup$
    – Xgk
    Jun 4, 2020 at 21:51
  • $\begingroup$ "where to start": Signals and Systems textbook, learn what a filter is :) it really helps! $\endgroup$ Jun 5, 2020 at 8:42

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IIR filters can be unstable, for this reaso high order filters are "divided" into smaller filters (which tend to be more stable). Imagine you have a an 8 pole filter, tou can transforme it to four second order filters that are executed in cascade (the output of one filter is the input of the next one)

https://www.mathworks.com/help/signal/ref/tf2sos.html

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