7.2. 1 Windows function method o Thus, given a frequency response specification Hd(e@,we can compute ha[n] using the above equation and hence determine the transfer function Hd (z) o However, for most practical applications, the desired frequency response is piecewise constant with sharp transitions between bands in which case the corresponding impulse response sequence thd[n] is of infinite length and noncausal7.2.1 Windows function method  Thus, given a frequency response specification Hd(ejω), we can compute hd[n] using the above equation and, hence, determine the transfer function Hd(z).  However, for most practical applications, the desired frequency response is piecewise constant with sharp transitions between bands, in which case, the corresponding impulse response sequence {hd[n]} is of infinite length and noncausal