impzlength Impulse response length 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 | digitalFilter | impz | zp2sos Ayush Baid