Answer the following questions with detailed justifications a) What is the bandwidth of the human voice? b) What is the bandwidth of our hearing process? c) What is the bandwidth used in mobile speech communications ? Solution a) A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech. In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. It is for this reason that the ultra low frequency band of the electromagnetic spectrum between 300 and 3000 Hz is also referred to as voice frequency, being the electromagnetic energy that represents acoustic energy at baseband. The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands, allowing a sampling rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN. Per the Nyquist–Shannon sampling theorem, the sampling frequency (8 kHz) must be at least twice the highest component of the voice frequency via appropriate filtering prior to sampling at discrete times (4 kHz) for effective reconstruction of the voice signal. b) Hearing range describes the range of frequencies that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, though there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. Sensitivity also varies with frequency, as shown by equal-loudness contours. Routine investigation for hearing loss usually involves an audiogram which shows threshold levels relative to a normal. Several animal species are able to hear frequencies well beyond the human hearing range. Some dolphins and bats, for example, can hear frequencies up to 100 kHz. Elephants can hear sounds at 14–16 Hz, while some whales can hear subsonic sounds as low as 7 Hz (in water). c) The present day telephone infrastructure limits the bandwidth of telephonespeech to 300–3400 Hz, whereby conversational speech falls mostly within 50–8000 Hz..

1. Answer the following questions with detailed justifications a) What is the bandwidth of the
human voice? b) What is the bandwidth of our hearing process? c) What is the bandwidth used in
mobile speech communications ?
Solution
a)
A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range,
that is used for the transmission of speech.
In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. It
is for this reason that the ultra low frequency band of the electromagnetic spectrum between 300
and 3000 Hz is also referred to as voice frequency, being the electromagnetic energy that
represents acoustic energy at baseband. The bandwidth allocated for a single voice-frequency
transmission channel is usually 4 kHz, including guard bands, allowing a sampling rate of 8 kHz
to be used as the basis of the pulse code modulation system used for the digital PSTN. Per the
Nyquist–Shannon sampling theorem, the sampling frequency (8 kHz) must be at least twice the
highest component of the voice frequency via appropriate filtering prior to sampling at discrete
times (4 kHz) for effective reconstruction of the voice signal.
b)
Hearing range describes the range of frequencies that can be heard by humans or other animals,
though it can also refer to the range of levels. The human range is commonly given as 20 to
20,000 Hz, though there is considerable variation between individuals, especially at high
frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal.
Sensitivity also varies with frequency, as shown by equal-loudness contours. Routine
investigation for hearing loss usually involves an audiogram which shows threshold levels
relative to a normal.
Several animal species are able to hear frequencies well beyond the human hearing range. Some
dolphins and bats, for example, can hear frequencies up to 100 kHz. Elephants can hear sounds
at 14–16 Hz, while some whales can hear subsonic sounds as low as 7 Hz (in water).
c)
The present day telephone infrastructure limits the bandwidth of telephonespeech to 300–3400
Hz, whereby conversational speech falls mostly within 50–8000 Hz.