Handbook for Sound Engineers

Psychoacoustics 57

not be noticeable for a person without perfect pitch.
However, for a senior musician with perfect pitch, he or
she might find it to be annoying when perceiving every-
one else in the orchestra playing out of tune. He or she
has to live with it, because he or she might be the only
one in the orchestra playing out of tune.

3.9.7 Other Pitch Effects

Pitch is mostly dependent on the fundamental fre-
quency, and normally the fundamental frequency is one
of the strongest harmonics. However, the fundamental
of a complex tone can be missing or masked with a nar-
rowband noise, while still producing a clear pitch.^43 The
pitch produced without fundamental is called virtual
pitch, and it is evidence favoring the temporal theory
over the place theory. The waveform of a virtual pitch
bears identical period as a normal complex tone includ-
ing the fundamental at the same frequency.
When listening to a broadband signal with a certain
interaural phase relationship, although listening with
one ear does not produce a pitch, when listening with
both ears, one can hear a pitch on top of the background
noise. These kind of pitches are called “binaural
pitches.”44,45

3.10 Timbre

Timbre is our perception of sound color. It is that sub-
jective dimension that allows us to distinguish between
the sound of a violin and a piano playing the same note.
The definition by the American Standards Association
states that the timbre is “that attribute of sensation in
terms of which a listener can judge that two sounds hav-
ing the same loudness and pitch are dissimilar,” and
“timbre depends primarily upon the spectrum of the
stimulus, but it also depends upon the waveform, the
sound pressure, the frequency location of the spectrum,
and the temporal characteristics of the stimulus.”^17 Each
sound has its unique spectrum. For musical instruments,
the spectrum might be quite different for different notes,
although they all sound like tones produced by the same
instrument. The timbre of a sound produced in a concert
hall may even vary with listener position because of the
effects of air absorption and because of the fre-
quency-dependent absorption characteristics of room
surfaces.
It is worth noting that, in order to more completely
describe timbre, both amplitude and phase spectra are
necessary. As the example in Section 3.5 shows,
although a white noise and an impulse have identical
amplitude spectra, they sound quite differently due to

the difference in the phase spectra. Sometimes the onset

and offset of a tone might be important for timbre (e.g.,

the decay of a piano tone). Thus, along with the consid-

eration of the time window of human hearing (on the

order of 100 ms), the most accurate description of a

timbre would be a spectrogram (i.e., the spectrum

developing with time), as shown in Fig. 3-19.

3.11 Binaural and Spatial Hearing

What is the advantage of having two ears? One obvious

advantage is a backup: if one ear is somehow damaged,

there is another one to use, a similar reason to having

two kidneys. This explanation is definitely incomplete.

In hearing, having two ears gives us many more advan-

tages. Because of having two ears, we can localize

sound sources, discriminate sounds originated from dif-

ferent locations, hear conversations much more clearly,

and be more immune to background noises.

3.11.1 Localization Cues for Left and Right

When a sound source is on the left with respect to a lis-

tener, it is closer to the left ear than to the right ear.

Therefore the sound level is greater at the left ear than

that at the right ear, leading to an interaural level differ-

ence (ILD). Sometimes, people also use the interaural

intensity difference (IID) to describe the same quantity.

Moreover, because the sound wave reaches the left ear

earlier than the right ear, there is an interaural time dif-

ference (ITD) between the two ears. However, the audi-

tory neurons do not directly compare ITD, and instead,

they compare the interaural phase difference (IPD). For

Figure 3-19. An example of a spectrogram: male voice of

“How are you doing today?” The vertical axis is frequency,

the horizontal axis is time, and the darkness of a point rep-

resents the level of a particular frequency component at a

given time.

20k

10k

7k

5k

3k

2k

1k

700

500

300

200

100

70

50

30

0.032 Time—ms/div 1.708

Left –30

–35

–40

–45

–50

–55

Relative amplitude—dB

Frequency—Hz