Magnitude response is the magnitude of the complex value of the frequency response vs. frequency.
It is used to see how a system affects the amplitudes of frequencies in a signal.

A variable’s amplitude is just a measure of change relative to its central position, whereas a variable’s magnitude is a measure of distance or quantity regardless of direction.

The power spectral density tell us the distribution of power of the signal vs. frequency. The PSD plots indicate most of the power is concentrated from 1Hz to 25 Hz which conforms with the intended configuration of the chirp in the time domain.

Sinusoidal signal is a smooth repetition of oscillation at a fixed frequency. Chirp signal is also a sinusoidal signal whose frequency continuously increases (or decreases).

FFT is taken on a vector of size L. Hence the amplitude is normalized by dividing by L. If the shape of the amplitude spectrum is important than the actual amplitude values, then the scaling factor can be ignored.

plot(f,abs(X)/(L),’r’);

Why abs(X) is divide by (L)? Can’t we just write plot(f,abs(X),’r’); only?

Thank You.