>> load('handel.mat')

t0=cputime;
Y=fft(y);
yTime=cputime-t0

yTime =

    0.4910

>> hallelujah=y(1:65536);
t0=cputime;
Y=fft(hallelujah);
yTime=cputime-t0

yTime =

    0.0770

>> [y_size, t]=size(y);
y_size

y_size =

       73113

>> % Since the original size of y is 73113x1 and hallelujah is 65536x1 ...
>> % hallelujah is smaller than y and hence requires less cpu time.