일 때, 그래픽 접근 방법으로 주파수 이동 성질을 확인해보자.

ex3_9.cem

n = 0:100; x = cos(pi*n/2);
k = -100:100; w = (pi/100)*k;        % frequency between -pi and +pi
X = x * (exp(-j*pi/100)).^(n'*k);    % DTFT of x%
y = exp(j*pi*n/4).*x;                % signal multiplied by exp(j*pi*n/4)
Y = y * (exp(-j*pi/100)).^(n'*k);    % DTFT of y% Graphical verification
subplot(1,1,1)subplot(2,2,1); plot(w/pi,abs(X));
xtitle("frequency in pi units"); ytitle("|X|")
title("Magnitude of X")subplot(2,2,2); plot(w/pi,angle(X)/pi);
xtitle("frequency in pi units"); ytitle("radiands/pi")
title("Angle of X")subplot(2,2,3); plot(w/pi,abs(Y));
xtitle("frequency in pi units"); ytitle("|Y|")title("Magnitude of Y")
subplot(2,2,4); plot(w/pi,angle(Y)/pi);
xtitle("frequency in pi units"); ytitle("radians/pi");
title("Angle of Y");