band pass filter matlab

Question

Think about I have an array of time and fundamental frequency of a given audio file. So what I need to do is extract the fundamental frequency from the audio. And what I am thinking is to apply a bandpass filter, for instance 100hz above and below to the given fundamental frequency corresponding to time.

Is it possible to do it? I know somehow it would be, but is there a known method that I can define the band pass filter parameters varying in time?

Thanks,

Baggio