Sound

A mechanical, Longitudinal, wave or or vibrations in space.

Mechanical Wave, Longitudinal Wave

2 (Nature of Sound)

Compressions

Regions of above normal pressure on a sound wave

Rarefractions

Regions of below normal pressure on a sound wave

Intensity

The measure of the sound's power density

Loudness

The intensity of the sound as perceived by the human ear

Pitch

The frequency of the sound

Ultrasonic

Above the Human Hearing

infrasonic

Below the human hearing

100 Hz to 1kHz

Typical sound produced by humans

4kHz

the peak sensitivity of human hearing is?

18kHz to 20kHz

upper frequency limit for human hearing

18Hz to 20 Hz

Lower Frequency limit for human hearing is

Speech

Refers to the human voice or the sound coming from the mouth of a talker

100Hz to 10kHz

Speech Frequencies ranging from

10uW to 1000uW

Speech power ranges from

1kHz to 3kHz

Maximum intelligibility for voice frequency is somewhere between

Speech Volume

The intensity of a speech, which may differ from one talker to another

Speech Measurement

Equation relating human voice (speech) power and volume units (VU)

Volume Unit Meter

A device used to measure speech volume

+4dBm on a 600 ohm line

human hearing with a standard signal level of

0dBm

for a pure since wave

-1.4dBm

for a complex signal like the human voice

18.6 dB

Typical talker power is about, higher than the average power

10 seconds

The average talker is taken for a period of time no longer than

Telephony

A long-distance communication process using an apparatus called a telephone

IP Telephony

A modern form of telephony that uses TCP/IP to transmit digitized voice over the w.w.w. or the internet

Voice Over Internet Protocol

VOIP

Telephone

An electronic apparatus that transform sound wave into an electrical wave, transmit this wave over a suitable medium

Telephone System/Network

A connection of two or more circuit that facilitates communication via a telephone

Analog Telephone Network, Digital Telephone Network

Two type of telephone

Alexander Graham Bell 1874

concluded that speech could be transmitted electrically over wire

1875 (June 2)

Assisted by Mr. Thomas Watson, experimented with a harmonic telegraph

1876 (February 14)

Bell applies for a patent for a telephone

1876 (March 7)

The patent was granted to bell

1877

The first telephone switchboard was installed in Boston, USA

1878

The first commercial telephone exchange, with 21 subscribers, was established in New Haven Connecticut

1880 (June 3)

Bell invented the photo phone

1884

First commercial telephone service was established between New York and Boston

1889 (Almond Strowger)

a patent for the first automatic telephone switch, later called strowger swtich.

William Gray

a patent for the first coin-operated telephone

1896

The first dial telephone goes into use in Milwaukee

1947

The first Microwave radio relay was employed

1956

The first transatlantic telephone cable between Newfoundland, Canada and Scotland was completed

1963

transpacific cable connecting British, Columbia, Canada to Australia and New Zealand was established

Mid 1960s

Satellite was used to relay transcontinental telephone signal

Rotary Dial Type, DTMF Type

Two types of telephone set

Transmitter (Mouthpiece)

It converts sound pressure into corresponding electrical variation

Transmitting Objective Loudness Rating

A measure in dB of the efficiency of the transmitter in converting acoustic pressure into an electrical output voltage

VT

Loudness output voltage of transmitter

Pm

Loudness sound pressure the mouth

Receiver (Earpiece)

It converts electrical pressure back into corresponding sound pressure

Receiving Objective Loudness Rating

A measure in dB of the efficiency of the receiver in converting electric source voltage into an acoustic pressure output

Switch Hook (Plunger)

Its function is to complete/close open the loop

On Hook

The phone handset is on its cradle or base and is idle

Off Hook

The phone handset is off the base and is in used or busy

Dialer

A circuit used to dial the number of the party that the telephone user wants to call

Rotary Dial, Touch Pad

Methods of Dialing

Pulse Dialing

A break and make method. That is, a method where the loop is break (open) and make (close) in a number of times corresponding to the number

A touch method. For every button pressed, a two-tone (dual frequency) signal is sent towards the CO