len = impzlength(b, a, tol)
-returns the impulse response length for the causal discrete-time filter
-with the transfer function coefficients for numerator and denominator in
-a and b respectively. For stable IIR filters, len is the effective length
-impulse response length, i.e. the length after which the response is
-essentially zero
-len = impzlength(sos)
-returns the impulse response length of the filter specified by second
-order sections matrix. sos is a Kx6 matrix, where K is the number of
-sections. Each row of the sos matrix corresponds to a second order
-biquad filter
-len = impzlength(__, tol)
-specifies a tolerance for estimating the effective impulse response
-length in case of an IIR filter. By default, tol is 5e-5. Increasing tol
-leads to shorter len and vice-versa
