Wiley signals and systems e book TLFe BO 298

11.3 Saniplirig 283 corresponding exponential term appears in the spectrum (11.52) Figure 11.24 shows the magnitude of the resulting spectrum X'(~.JJ).While in Figure 11.22 the hascband sycctrum was weighted with a si-lunction and then periodicidly continued, here thc periodic spectrum X ( j w ) is already provided arid is then weighted by niultiplyirig it with the si-function This damps tlie reorcurienres of the bascbaiid (shaded in Figure 11.24), but unfortunately does not fully suppress thern 'She shaded area could, for example he audible high-frequency noise in an audio signal or appear in an imtzge as visibly 'blocky' pixel5 However, unlike ahsiiig errors which cannot be separated from the desired signal, tliese noise components can be fully eliminat8eclby post-connecting a imv-pass filter with iunpulsc response h(t) (1i 35) The residual reduction in high-frequency components in tlie baseband can likewise by coinpensated for using a filter which can 1~ iinplemc'rited either digitally before the DAC or after as an analog filter - T T I'igure 11.24: Magnitude response l X ' ( j w ) l of tlir signal irtterpolated with sample-adhold circuit Example 11.2 The problems described with reconstruction also occur in film projections Recording and replaying it srries of individual images can be considered as sampling of a scme continuously changiizg in the t i ~ e - d o r ~ ~ i i Per i n second, 24 individid images are t a b i i , so the sampling frequency is f I - - = 24B~ "-T