TideMan <firstname.lastname@example.org> wrote in message <email@example.com>... > On Tuesday, April 23, 2013 10:59:08 AM UTC+12, ghasem wrote: > > > Well, when you do the Fourier Series summation, just leave out the components with frequencies greater than f1. > > > > ========================== > > > > exactly,my problem is here.I want to remove frequencies higher than f1,but I don't know how code it in MATLAB? > > > > for example,following code is imperfect.please perfect it. > > > > data1 = rand(1,n) % suppose data1 is my data. > > > > data2 = dct(data) % data2 is discrete cosine transform of data1. > > > > > > > > % now!How draw it's figure in discrete frequency domain and leave out f > f1 ? > > > > ghasem > > Interval in frequency is: > df=1/(2*N*dt); > where N is no of data and dt is the interval between data. > f1 corresponds to index no: > indx=round(f1/df); > So, for dct Y: > Y(indx:end)=0; > y=idct(Y);
You might want to consider a time domain window to prevent aliasing.