How to convert from time domain to frequency domain?

I have this filter:

filter_2 = firceqrip(2,0.6,[0.05 0.03]);

I want to convert it to the frequency domain to multiply it by a signal (i.e filter in the frequency domain)

Answer 1

[Image Analyst]

Call fft() or pwelch().

[MatlabGirl]

so I only do fft(filter_2,N) ??

[Image Analyst]

Yeah, but why use N?

[MatlabGirl]

I don't know, that's how we always do it.

Are you sure its fft(filter_2)

shouldn't we do fft(h) with h being the impulse response?

The purpose of what I am trying to do is filter the a signal in the frequency domain using filter_2 the signal is a group of sinusoids

[Image Analyst]

But you're not filtering an impulse with filter_2 are you? You're filtering a signal with a filter, filter_2.

[MatlabGirl]

I see. thank you :)