# FIR Filter Magnitude Response

This is the shape of the bipolar amplitude function for a FIR filter with odd m:

I have 2 questions :

1. If i want to use this FIR as a low pass filter between 0 and $$\frac{F_{c}}{2}$$ , how can i set the value of $$G(f)$$ to 0 between $$\frac{F_{c}}{2}$$ and $$F_{c}$$ ?

2. My prof said that i can use the this FIR as a lowpass between 0 and $$\frac{F_{c}}{2}$$, but if i want to use the filter between $$\frac{F_{c}}{2}$$ and $$F_{c}$$ does it still behave as a lowpass ? (what does it mean that in that range $$G(f)$$ takes negative values ? )

• this isn't even a low pass between 0 and $F_c/2$, even if it was a good idea to zero-force the rest, so I'm not even sure where this is coming from or going to. – Marcus Müller Jan 14 at 8:54
• also, a how did you determine this $G(f)$? this doesn't look like it was done with the tools you could apply to a discrete-time system like your FIR filter probably is. – Marcus Müller Jan 14 at 8:56
• It's on a slide did by my prof. You can watch it here ibb.co/4FYxvVL – themagiciant95 Jan 14 at 10:10
• The figure on the slide looks different from the one in your question. – Matt L. Jan 14 at 10:15
• I'm sorry wrong slide, ibb.co/YjjdW3T – themagiciant95 Jan 14 at 10:23