Why does an 8 point DFT behave differently from a 16 point?

1. How does the length of a signal affect the DFT?
2. Why is the DFT mirrored?
3. Which sequences has a real valued 8-point DFT?

How does the length of a signal affect the DFT?

The length N of the DFT is the number of frequency points that will result in the DFT output. Zero padding will result in more frequency samples, however this does not increase frequency resolution, it just interpolates samples in the DTFT.

Why is the DFT mirrored?

Because both the positive and negative frequency sinusoids are 90 degrees out of phase and have the same magnitude, they will both respond to real signals in the same way.

Which sequences has a real valued 8-point DFT?

The first points of 8-point DFT of real valued sequence are0.25,0.125-j0. 3018,0,0.125-j0.