Functions > Signal Processing > Digital Filtering > Time Response of Digital Filters
Time Response of Digital Filters
response(v, C1, n)—Returns an n element vector giving the response of input vector v to an FIR or IIR filter with coefficient array C1. This function uses direct evaluation of the convolution. For a long input signal, this method can be quite slow.
fftfilt(v, C2, [nfft])—Returns a vector giving the response of input vector v to an FIR filter with coefficients C2. This function applies the DFT of optional length nfft to successive segments of the input, then combines the results with the overlap-add method.
 • If the final transient response is desired, zero pad the input signal to the appropriate length, and then increase n. • For an IIR filter, response must always be used. • For an FIR filter with an impulse response much shorter than the input signal, fftfilt may be used, and often provides a faster result. • If nfft > length(x) + length(C) −1, then fftfilt does not use the overlap-add method. Instead, it convolves the signal and filter in one step in the Fourier domain, after zero-padding the signal and filter vectors so that they are the length of nfft. • The IIR transfer functions must be normalized so that the constant term in the denominator is 1.
Arguments
v is a real or complex-valued signal vector or multichannel matrix, filtered individually by column.
C1 is a real or complex-valued vector (FIR) or two-column matrix (IIR) of filter coefficients. In the case of an IIR filter, the first column contains coefficients of the numerator, the second contains coefficients of the denominator.
C2 is a real or complex-valued vector of FIR filter coefficients.
n is a positive integer, the size of the output vector, no greater than the length of the input.
nfft (optional) is a positive integer, the length of the FFT in the overlap-add method. It may not be greater than the length of the signal. If omitted, nfft is the length of the filter.