I am trying to implement an FIR filter with a Blackman window function. The solution I got for my signal filtering problem is to have different window sizes for certain characteristics of the input signal. My current solution uses a set of filters working in parallel and the output switches between them based on the input signal characteristics. However, some discontinuities may occur in the output signal. My question: Is there an efficient way to implement an FIR filter with variable (or adaptive) window size or this whole idea is unreliable?