STRATEGIC INTERVENTION MATERIAL

communication
-is the transmission and reception of meaningful information. people communicate through their senses. Normally, they communicate with each other within range of sight and hearing by visual and vocal means, that is , by light and sound.


Through various technological devices such as the telephone, telegraph, radio, television, radar, radio telescope orbiting satellites, microwave relays, and lasers as well as the advances made in the field of electronics, human communication is the beneficiary of immeasurable favor. Until now, barriers of time and distance prevented efficient and speedy interaction. 
Nature of Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.

^{Sound is what we hear:

VIBRATIONS shake the AIR

AIR shakes the EARDRUM

NERVES sense the SHAKE

BRAIN feels the SOUND}

^{Different sounds:}

^{LOUD/SOFT

HIGH/LOW pitch

SHORT/LONG}

Electronic vocal communication devices such as the telephone require the mutual conversion of sound and electricity.

We live in a world of sound. Anywhere we go and whatever we do, we hear sounds. Some of these
are familiar to us, a friend's voice, the chirping of birds, the ticking of the clock, the barking of the dogs, the beating of your heat. Certain sounds like music are pleasant to the ears; others are not. We call the latter noise. Different sounds have different effects. For instance, music soothes and relaxes. The crashing sounds of explosives can make us feel nervous.

Sound is restricted to the frequency range of 20 Hz to 20 000 Hz to which human ear is sensitive. waves with frequencies below this audible range are called infrasounds and those above or greater than 20 000 Hz are reffered to as ultrasounds.

Sound waves are longitudinal waves. they are produced by a series of vibrations parallel to the direction of travel of the waves. When you pluck the strings of a guitar, the strings look hazy as they vibrate. Touch your throat while talking and you will feel the vibrations of your vocal cords. When you ring a bell, you pull the string and move it back and forth to produce sound. In each of these examples, the source of sound is a vibrating object.

Propagation of sound waves

How do sound waves spread or propagate from the source toward the space around it? What kind of medium is needed for their propagation?

Like water waves, sound waves need a medium to spread in.Sound is a sequence of waves of pressure which propagates through compressible media such as air or water. They can even travel through narrow openings and around corners, but not in an empty space or vacuum.

The behavior of sound propagation is generally affected by three things:

A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium.

The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported.

The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).

Considering a vibrating tuning fork. As the prongs of the fork move back and forth, they disturb air molecules close to them creating a back and forth movement of the air parallel to the direction of the waves. These air molecules likewise transfer their motion to the neighboring particles and to the other molecules. The air molecules then strike your eardrum, making it vibrate. Nearly all sounds reach you with air as the transmitting medium. Dense gases are better transmitters of the sounds than rare gases, as you climb a mountain, you must speak a little louder to be heard. Air on mountains is less dense than in the lowlands. It does not transmit sound so readily.

Perception of sound

For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz), although these limits are not definite. The upper limit generally decreases with age. Other species have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz. As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and communication. Earth's atmosphere, water, and virtually any physical phenomenon, such as fire, rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound. In some species, these produce song and speech. Furthermore, humans have developed culture and technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound.

Sound wave properties and characteristics

Sound waves are often simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties:

Sometimes speed and directions are combined as a velocity vector; wave number and direction are combined as a wave vector.

Transverse waves, also known as shear waves, have the additional property, polarization, and are not a characteristic of sound waves.

Speed of sound

The speed of sound depends on the medium the waves pass through, and is a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium to its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 °C (68 °F) air at the sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph) using the formula "v = (331 + 0.6T) m/s". In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph). The speed of sound is also slightly sensitive (a second-order an harmonic effect) to the sound amplitude, which means that there are nonlinear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see parametric array).

Acoustics

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical or audio engineer. The application of acoustics can be seen in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Noise

Noise is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal.

Sound pressure level

Sound pressure is the difference, in a given medium, between average local pressure and the pressure in the sound wave. A square of this difference (i.e., a square of the deviation from the equilibrium pressure) is usually averaged over time and/or space, and a square root of this average provides a root mean square (RMS) value. For example, 1 Pa RMS sound pressure (94 dBSPL) in atmospheric air implies that the actual pressure in the sound wave oscillates between (1 atm $-\sqrt{2}$ Pa) and (1 atm

that is between 101323.6 and 101326.4 Pa. Such a tiny (relative to atmospheric) variation in air pressure at an audio frequency is perceived as a deafening sound, and can cause hearing damage, according to the table below.

As the human ear can detect sounds with a wide range of amplitudes, sound pressure is often measured as a level on a logarithmic decibel scale. The sound pressure level (SPL) or L_p is defined as

where p is the root-mean-square sound pressure and p_ref is a reference sound pressure. Commonly used reference sound pressures, defined in the standard ANSI S1.1-1994, are 20 µPa in air and 1 µPa in water. Without a specified reference sound pressure, a value expressed in decibels cannot represent a sound pressure level.

Since the human ear does not have a flat spectral response, sound pressures are often frequency weighted so that the measured level matches perceived levels more closely. The International Electrotechnical Commission (IEC) has defined several weighting schemes. A-weighting attempts to match the response of the human ear to noise and A-weighted sound pressure levels are labeled dBA. C-weighting is used to measure peak levels.

Characteristics of Sound waves.

How do sounds differ? The crack of thunder may be very loud; a whisper may be soft and low. A cicada sound is shrill; a dog’s growl is like a deep bass. Some voices have pleasing quality, while others are harsh or grating. These examples indicate that sounds differ. Each is distinct from the others. Sounds may be regarded as “fingerprints” of the persons or objects producing them. They differ from one another in 3 ways, namely; (a) loudness or intensity (b) pitch (c) quality.

LOUDNESS AND INTENSITY

If a small pebble were thrown with force into the water, the waves to be produced would have greater amplitude than if the pebble were dropped into the water gently. The amplitude is the maximum displacement from a wave’s equilibrium position.

Energy is always carried by sound waves. A vibrating body, like the guitar string or the drumhead, produces loud songs when much energy is transferred to it. Sound waves transfer energy through the particles of the medium. In studying and detecting sounds within the body, doctors use the stethoscope, which has a rubber tubing attached to an end piece that is placed on the area to be examined. The tubing transmits the sounds from the patient’s diaphragm to the doctor’s ears.

Sound is a form of mechanical vibration which propagates through any mechanical medium. It is closely related to the ability of the human ear to perceive sound. The wide outer area of the ear is maximized to collect sound vibrations. It is amplified and passed through the outer ear, striking the eardrum, which transmits sounds into the inner ear. Auditory nerves fire according to the particular vibrations of the sound waves in the inner ear, which designate such things as the pitch and volume of the sound. The ear is set up in an optimal way to interpret sound energy in the form of vibrations.

Pitch

Sounds are low, others are high. The highness or lowness of sounds is called pitch, a characteristics determined by our senses. The frequency of sound waves determines the pitch of a sound, the higher the frequency of a sound wave, the higher the pitch.

Pitch represents the perceived fundamental frequency of a sound. It is one of the major auditory attributes of musical tones along with duration, loudness, timbre, and sound source location.

Pitches are compared as "higher" and "lower" in the sense that allows the construction of melodies. Pitch may be quantified as a frequency in cycles per second (hertz), however pitch is not a purely objective physical property, but a subjective psychoacoustical attribute of sound.

Pitch is a subjective sensation in which a listener can assign tones to relative positions on a musical scale based primarily on the frequency of vibration. Pitches are sometimes quantified as frequencies (cycles per second, or hertz), by comparison with sine waves. Pitches in Hz usually match very nearly the repetition rate of sound waves other than sine waves, too

The beginning of electronic communications

Electronic communications is any communication based on electricity. The basis for this wasn’t properly harnessed until both direct current and alternating current electricity were mastered and popularized in the late 19^th century. Thomas Edison warned that direct current electricity was safer, and thus should form the basis of a national power company. Unfortunately, alternating current electricity had better transmission capabilities and although it is more dangerous, became the basis for modern electrical power. These basic truths would ultimately form the foundation for modern electronic communication. All communications formed with alternating electrical current will be investigated.

What we know of as electronic communications originated with the telegraph. The telegraph was a simple electrical circuit that transmitted electrical impulses across country via wire. It had two signals, a dot and a dash. This formed a code that could be interpreted as words. This code was Morse code. Over time, the code would be translated into all languages and became state-of-the-art technology.
The next major communications invention was the telephone. The “plain old telephone” has changed very little since it was invented in the early 19^th century. It has just become more popular and accepted since its invention. It was patented by Alexander Gram Bell in 1876 but more than likely invented by Innocenzo Manzetti and was originally called the “speaking telegraph”. The history indicates that the telephone as actually being demonstrated in England some nine years before Alexander Bell filed his patent in America. The idea that the phone was invented in America is a misconception. Regardless of its origins, there was nothing as convenient as the phone until wireless radio transmissions became fashionable quite a while later.
The idea of sending messages via radio waves didn’t become popular until Faraday proved that such transmissions were possible and done easily and cheaply. Wireless transmissions evolved from simple messages with ranges of only a few miles to the cellular phones we use today. Wireless transmissions eventually have become the premier communications medium. Wired transmissions are looked at as backwards and troublesome in comparison. This viewpoint comes from the fact that wires are prone to trouble. Cables break, get dug up and become disconnected from equipment. Virtually every wired industry in the world today wishes to become wireless. There are many business benefits to dropping the cable. The most important of which is to increase reliability. Today customers see wires as a weakness and low standard of technology. Modern communications, with the way cell phones work, have grown by leaps in bounds in terms of size, scale and the ability to reach others. Now a person with just a satellite phone can call someone on the other side of the planet without an operator and complex operation. This was unthinkable just 50 years ago.

A brief history of electronic communication

Communication is as old as humankind - and indeed as old as our evolutionary ancestors.

Until the dawn of electronic communication, rapid communication was limited to the distance we could shout or see.

Communication at a distance was limited to the speed of a person, a horse or a boat (or a chain of beacons or visual semaphores).

Electronic communication has enabled us to communicate:

over much greater distances - even as far as space probes to the planets
quickly - electronic communication occurs at or close to the speed of light
large amounts of information
cheaply
with large numbers of people - most people in industrial countries have access to TV, radio, telephones etc.

This radical change in communication technology has been associated with profound changes in our lives - socially, for business and industry, our knowledge of the world and the ability of others to educate, persuade, inform, entertain and mislead us.

Because electronic communications systems often involve millions of separate ‘Sending’ and ‘Listening’ subsystems e.g. telephones, radios or TV sets they cannot be redesigned quickly. So, for example, the Morse telegraph led to the conventional telephone, which in turn led to the mobile telephone. The modern mobile telephone includes features that date back to the telegraph of more than 160 years ago. In fact it was only in 2000 that Morse Code ceased to be taught in wireless telegraphy courses.

The telephone system

The system

The University of St Andrews telephone system employs an Ericsson MD110 (running BC12.2 software) with 17 Line Interface Modules (LIMs), distributed in 5 exchanges throughout the University. These LIMs connect approximately 6700 digital and analogue extension ports to the system. (8000 extensions max.). The 5 exchanges are linked by a University owned, dedicated optical fibre Broadband Premises Network (BPN) utilising Fibre Distributed Digital Interface (FDDI) protocol at 100Mbs. Each exchange is connected to the BPN via Ericsson multiplexor units.
With effect from 01 February 2003 the University has provided telephone services for the student population living in University owned Halls of Residence (ResTel). Of the 6700 total extensions in use in the University approximately 3600 are in student residences. Ericsson's DNA software is used by the Telephone Office to administer moves and changes on a daily basis, including defining classes of service and category set-ups.

Voice mail

The University uses Call Express for its voice mail system to provide voice mail services for staff and Students on a single platform.

Call logging

The Telecoms and Infrastructure Manager is actively involved in developing a number of interlinked programs, utilising the data generated by the MD110, in Microsoft Visual Basic 6 in order to analyse the running telephone system and to ensure its effective use by staff and students.

Rapid long-distance communication relies on the telegraphed until 1877.

The foundation of electronic communication begins with the introduction of the electromagnet. The British inventor William Sturgeon (1783-1850) displayed the power of the electromagnet. He uses seven-ounce piece of iron, wrapped with wires which was sent with a current from a single cell battery, and was able to lift nine pounds of object.

An American named Joseph Henry (1797-1878) was able to demonstrate Sturgeons device for long distance communication. It was done by sending an electronic current over a mile of wire to activate an electromagnet, this activity causes a bell to strike. This was the beginning of the use of the telegraph.

            The telegraph is a device which uses electricity to send messages. The telegraph was developed by Samuel F.B Morse. He is a professor at the New York University. Samuel Morse used a telegraphed key to encode messages. This was done by using a special code called the Morse Code. This code was consisted of dot and dashes representing the letters of the alphabet and made by making and breaking the transmitter circuit. The pulses of the current deflected an electromagnet, which moved a marker to produce written codes on a strip of paper. The following year, the device was modified to emboss the paper with dots and dashes.

   Later, the operation developed into sending by key and receiving by ear. The electric signals are sent through wires to the receiver end where the received signals are converted to sound by a sounder. A trained Morse operator could transmit 40 to 50 words per minute.

     Until 1877, all rapid long distance communications depended upon the telegraph. That year, a rival technology developed that would again change the face of communication --------- the telephone.

The Telephone System

Alexander Graham Bell's success with the telephone came as a direct result of his attempts to improve the telegraph.

Born on March 3, 1847, in Edinburgh, Scotland, Alexander Graham Bell was the son and grandson of authorities in elocution and the correction of speech. Educated to pursue a career in the same specialty, his knowledge of the nature of sound led him not only to teach the deaf, but also to invent the telephone.

The Telephone

Bell's extensive knowledge of the nature of sound and his understanding of music enabled him to conjecture the possibility of transmitting multiple messages over the same wire at the same time. Although the idea of a multiple telegraph had been in existence for some time, Bell offered his own musical or harmonic approach as a possible practical solution. His "harmonic telegraph" was based on the principle that several notes or signals differed in pitch. They had proven that different tones would vary the strength of an electric current in a wire. To achieve success they therefore needed only to build a working transmitter with a membrane capable of varying electronic current and a receiver that would reproduce these variations in audible frequencies.

STRATEGIC INTERVENTION MATERIAL

Sunday, February 20, 2011

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