1. Why is the amplitude spectrum important?
Why is the phase spectrum unimportant?

2. Amplitude spectra of [s] and [S]. Which is which? How can you tell?
Frequency
p.s. On each plot, there is a jiggly black curve and a smoother red curve. The black ones are Fourier amplitude spectra. What are the smoother red ones?

3. Amplitude spectra of [s] and [S]. Which is which? How can you tell?
Frequency
Answer: The smooth red curves are spectrum envelopes.

4. Phase spectra of [s] and [S].
Which is which?
Can’t tell? Neither can I.
The two phase spectra are different, but (unlike the amplitude spectra) not in any predictable way.

5. Moral: The amplitude spectrum tells you something useful about the nature of the sound. (It tells you what frequencies are present at what amps.) The phase spectrum does not. This is why the ear goes thru all the trouble to get rid of the phase information.
[S]
[s]