Why is the amplitude
spectrum important?
Why is the phase spectrum
unimportant?
Amplitude
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?
Amplitude spectra of [s] and [S].
Which is which? How can you tell?
Amplitude
[s]
[S
]
Frequency
Answer: The smooth red curves are spectrum envelopes.
Phase spectra of
[s] and [S].
360
Phase (degrees)
300
240
Which is which?
180
120
60
0
0
800
1600
2400
3200
4000
Frequency (Hz)
4800
2400
3200
4000
Frequency (Hz)
4800
5600
6400
360
Phase (degrees)
300
240
180
120
60
0
0
800
1600
5600
6400
Can’t tell? Neither
can I.
The two phase
spectra are different,
but (unlike the
amplitude spectra)
not in any
predictable way.
300
Phase (degrees)
Moral: The amplitude
spectrum tells you
something useful
about the nature of
the sound. (It tells you
[S
]
360
240
180
120
60
0
0
800
1600
2400
3200
4000
Frequency (Hz)
4800
2400
3200
4000
Frequency (Hz)
4800
5600
6400
at what amps.) The
[s]
360
Phase (degrees)
300
240
180
120
60
0
0
800
1600
what frequencies are present
5600
6400
phase
spectrum does not.
This is why the ear
goes thru all the
trouble to get rid of
the phase information.