d. Noise. Looking at waveforms one can distinguish either speech or music by the irregularity of its waveform.
If you examine the waveform illustrated in figure 5 you will notice a regularity of variation in the speech and music.
Portions of the wave recur at regular intervals in A and B while in the waveform representing noise (C) there is no
perceptible regularity. This results in a relatively unpleasant sensation. You will find it is also difficult to determine the
frequency content of noise. At times the random or background noise in a room has a disturbing effect on a listener, and
may actually render a conversation unintelligible. Speech or music when it becomes distorted and unintelligible becomes
mere noise.
8.
Characteristics of Sound.
All sound produced by musical instruments and the human voice has three identifying characteristics: pitch,
loudness, and timbre.
a. The Pitch of Sound. The pitch of a sound is determined by its frequency. The voice of a soprano is higher in
pitch than the voice of a basso, the yowling of an alley cat is higher in pitch than the sound of a fog horn. In the case of a
complex wave, the pitch is determined by the fundamental frequency. The higher the frequency the higher the pitch. The
highest frequency the human ear can detect is about 20,000 cycles per second (cps) and the lowest is about 20 cycles
(cps). There are some sounds with frequencies well above the audible range (above 20,000 cps) they are called
ultrasonics. Low in the audible range is the musical standard pitch which is 256 cps. The common name for this musical
standard is middle "C."
b. Loudness of Sound. The loudness, the intensity, or the strength of the sound refers to the amount or strength
of the sensation it creates in the human ear. The measurement of sound intensity is sometimes expressed in watts per
centimeter. An instrument used to measure the loudness of sound accurately is a sound level meter. We find the loudness
of a sound depends on two factors. The amplitude of vibration of the source which determines the amplitude of the sound
produced and the distance between the source and the ear or measuring instrument. An example of this last statement is;
the harder a drum is hit the louder the sound or the longer the amplitude of the vibration. Recognize also the further away
you stand from the drum the weaker the sound is. Another way we can express the loudness of a sound is by saying; the
amplitude of a vibration depends on the amount of energy imparted.
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