If the samples are not "delta function" samples but are of finite width, then the spectrum of the sampled signal is no longer periodic but fits within a SINC envelope. This not only affects the spectrum about 1,2,3 etc times the sampling frequency but also affects the portion of the spectrum between 0 and ½ the sampling frequency. The effect is illustrated below for a triangular spectrum of the analog signal. Green curve shows the spectrum between 0 and ½ the sampling frequency for delta function samples, orange couve shows the spectrum between ½ the sampling frequency and the sampling frequency for delta function samples. For finite width pulses, the SINC envelope is shown in red, the resulting spectrum of the sampled signal is shown in cyan and the response of an

© 1999 Cuthbert A. Nyack.