Although lower frequency of vibration. However, the loudness

Although voice
processing has always been researched for past few decades, it is primarily in
the past few years that the technology has matured sufficiently to leave the
research laboratory and enter the real world for a wide range of applications (Rabiner,
1994). According to Rabiner (1994), this is due to the rapid advancement in
computing capability provided by modern digital signal processing (DSP) chips,
the sharp decrease in cost of computation and memory, and the increased
emphasis on providing high-quality communications services. It is crucial to
understand that voice source contains important information of the pitch and
loudness (n.a., 2016). The pitch of the sound depends on the frequency of
vibration. If the frequency of vibration is higher, the sound is shrill and has
a high pitch. Oppositely, the sound is said to have lower pitch if it has a
lower frequency of vibration. However, the loudness of a sound depends on the
amplitude and energy of the sound wave. It means the greater the energy, the
louder the sound is and the greater the amplitude (height) of the sound wave is
as well. Mathematically, the sound loudness is directly proportional to the
square of the amplitude of vibration and measured in decibel unit (Physics,
1999). This means that if the amplitude of sound wave becomes double then the
loudness of the sound will be quadruples.

          Similarly, human hearing range depends
on both the pitch and the loudness of the sound (Widex, n.d.). Human beings can
hear the frequency range approximately from 20Hz to 20kHz (Kumar, Shastri, and
Signh, 2011). According to Widex (n.d.), 20Hz to 20kHz forms the absolute
borders of the human hearing range, therefore, human hearing is most sensitive
in the frequency range from 2000Hz to 5000Hz. Furthermore, loudness is also
concerned in human hearing. Widex (n.d.) had stated that most human without
hearing disabilities can hear starting at 0 decibel (dB). For examples,
refrigerator humming sound is about 45 dB, conversation at normal level is
about 60 dB, heavy city traffic is about 85 dB, a motorcycle is about 90 dB,
MP3 player at maximum value is about 105 dB, siren is about 120 dB, and
firearms is about 150 dB (Steding, n.d.). However, sound with more than 85 dB
can be dangerous for human hearing in the case of prolonged exposure.