matlab的fft

能量守恆 sum(x.^2) = (abs(fft(x)).^2) / length(x) 幅度與時域對應 y = abs(fft(x)); dc_y = y(1) / length(x); ac_y = y(2:end) * 2 / length(x); 插零 y1 = zeros(512, 1); y1(1:2:end) = abs(fft(x, 256)); % x有256點 y2 = ab

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