Page 118 - Master Handbook of Acoustics

correspondingly greater than speech, as would be expected. Here again, long time averages are used
in establishing the boundaries of the music area, and the boundaries should be fuzzy to show
extremes. The music area shown is very conservative; it has a dynamic range of about 75 dB and a
frequency range of about 50 to 8,500 Hz. This frequency span is about 7.5 octaves, compared to the

10-octave range of the human ear. High-fidelity standards demand a much wider frequency range than
this. Without the averaging process involved in establishing the speech and music areas, both the
dynamic range and the frequency range would be greater to accommodate the short-term transients
that contribute little to the overall average but are still of great importance.

FIGURE 5-12 The portion of the auditory region utilized for music sounds.

Noise

The word “signal” implies that information is being conveyed. Noise can also be considered an
information carrier. Interrupting noise to form dots and dashes is one way to shape noise into

communication. We will also see how a decaying band of noise can give information on the
acoustical quality of a room. On the other hand, there are many types of noise that are undesirable,
such as dripping faucets and busy traffic. Sometimes it is difficult to distinguish between
objectionable noise and a legitimate carrier of information. For example, the noise of an automobile