Sample Width and Spectrum.
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 equalisation filter required to correct the spectrum
is shown in magenta.
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© 1999 Cuthbert A. Nyack.