resolving interharmonic from sin signal

Hi all, my aim is resolve an interharmonic from sinus signal.

Fs=25600; % T = 1/Fs; % Sample time T=1/Fs; % L = 1000; % Length of signal L=5120 t = (0:L-1)*T; % Time vector fo=50; f1=52; y = 10*sin(2*pi*fo*t) + 5*sin(2*pi*f1*t);|

 To do it ı must use dft. So ı implement a fir lowpass filter(window type kaiser fc 52 hz) with fftfilt command. İs this true for my aim. İf not how can i do?
thanks