Sound is a travelling wave that is an oscillation of pressure transmitted through a medium. Humans can hear sounds between 20-20,000 Hz. Sound speed depends on the medium and is faster in solids than liquids and gases due to closer particle packing. Noise is an unwanted sound that can cause hearing damage at high volumes. The ear detects sound waves which are then transmitted to the brain. Properties of sound waves include wavelength, amplitude, and frequency which determine pitch. Ultrasound has a frequency above human hearing range.

2.  Sound
Sound is nothing but a travelling 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. Human
beings can hear a sound from 20hertz(Hz) to 20000hertz(Hz)(20KHz).
Sound is Transmitted by either Longitudinal and transverse waves. The
speed of sound depends on the medium the waves pass through, and is a
fundamental property of the material. Sound is useful and dangerous/
harming too. It can be used as a signal in security related matters and it
can be dangerous as it can harm small children or old people and can result
in something wrong happening . Loud sound is known as noise and it can
result in hearing loss.
 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.

3.  For humans, hearing is normally limited to frequencies between about
12 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.

4.  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 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).

5. The easiest way to measure sound is with a output meter.
The procedure is given below :-
With an Output Meter
1. Make sure that your equipment is properly connected. Consult the user's
manual to determine which inputs and outputs are necessary for your
project.
2. Test your equipment by running some type of audio. It can be a voice
through a microphone or something pre-recorded. If you are able to hear
the audio, it means that everything is connected and working properly.
3. Begin running your audio (either voice or sound through a microphone
or a pre-recorded audio clip). Monitor the audio output meter on your
equalizer or mixing board. It will give you a reading on the levels of your
audio.

6.  The frequency is the number of wave crests per unit time that pass a fixed
location
 Wavelength is the – the distance over which the wave's shape repeats.
 The sensation of a frequency is commonly referred to as the pitch of a sound.
 A source of light can have many colors mixed together and in different
amounts (intensities). A rainbow, or prism, sends the different
frequencies in different directions, making them individually visible at
different angles. A graph of the intensity plotted against the frequency
(showing the amount of each color) is the frequency spectrum of the
light

7.  Sound effects or audio effects are artificially created or enhanced sounds,
or sound processes used to emphasize artistic or other content of films, television
shows, live performance, animation, video games, music, or other media. In
motion picture and television production, a sound effect is a sound recorded and
presented to make a specific storytelling or creative point without the use of
dialogue or music. The term often refers to a process applied to a recording,
without necessarily referring to the recording itself. In professional motion picture
and television production, dialogue, music, and sound effects recordings are
treated as separate elements. Dialogue and music recordings are never referred to
as sound effects, even though the processes applied to them, such as reverberation
or flanging effects, often are called "sound effects".
Video games
 The principles involved with modern video game sound effects (since the
introduction of sample playback) are essentially the same as those of motion
pictures. Typically a game project requires two jobs to be completed: sounds must
be recorded or selected from a library and a sound engine must be programmed so
that those sounds can be incorporated into the game's interactive environment.

8.  The sensation of a frequency is commonly referred to as the pitch of a sound.
 Amplitude is the magnitude of change in the oscillating variable with
each oscillation within an oscillating system.
 For example, sound waves in air are oscillations in atmospheric pressure and
their amplitudes are proportional to the change in pressure during one oscillation.
If a variable undergoes regular oscillations, and a graph of the system is drawn
with the oscillating variable as the vertical axis and time as the horizontal axis, the
amplitude is visually represented by the vertical distance between the extreme of
the curve.
 Propagation means "movement through" something in this context. You can
study the propagation of sound through air, for example, the most common kind
of sound there is for people. Sound propagates through water as well, as you can
easily prove by taking a dip in the pool. Does sound propagate through a vacuum?
Does it propagate through other materials? These are testable questions.

9.  Sound is transmitted by particles (atoms or molecules) in a solid, liquid or gas colliding
with each other. It is a wave which is created by vibrating objects and propagated through a
medium (solid, liquid or gas) from one location to another.
 Solids are made up of particles (atoms) that do not move about because they are closely
packed (touching each other) and held together by strong intermolecular forces. Therefore,
they are always in a fixed position and can only vibrate in a fixed position, sending sound
waves along its path very fast.
 In liquid, the particles are constantly moving and so the particles change their position, but
they are not fixed to each other that strongly as they are in a solid. They can also vibrate and
collide with other of their particles over a short range. This is because the attractive forces
are not strong enough to hold them in a fixed position. So, sound will travel slightly less
fast through Liquids.
 In gas, particles in gases are very far apart from each other. They can vibrate as well as move
freely and randomly in all direction. there is no force of attraction between gas particles. Gas
molecules must move quite a distance before they collide with other molecules. Sound energy
cannot move as quickly when the molecules are not in contact with each other. sound waves
traveling through this medium, will be much slower than that of a liquid and a solid respectively.

10. All waves have certain properties. The three most
important ones for audio work are shown here:
 Wavelength: The distance between any point on a
wave and the equivalent point on the next phase.
Literally, the length of the wave.
 Amplitude: The strength or power of a wave
signal. The "height" of a wave when viewed as a graph.
 Higher amplitudes are interpreted as a higher volume,
Hence the name "amplifier" for a device which increases
amplitude.
 Frequency: The number of times the wavelength occurs
in one second. Measured in kilohertz (Khz), or cycles per second.
The faster the sound Source vibrates, the higher the frequency.
 Higher frequencies are interpreted as a higher pitch. For
when you sing in a high-pitched voice you are forcing your vocal
chords to vibrate quickly.

11. Speed of sound is the distance traveled per a unit of time by a sound
wave propagating through an elastic medium. In dry air at 20 °C (68 °F), the speed
of sound is 343 metres per second (1,125 ft/s). This equates to 1,236 kilometres per
hour (768 mph), or about one kilometer in three seconds or approximately one
mile in five seconds. The speed of sound in air is referred to as Mach 1 by
aerospace professionals.
Speed of sound = 331.4 m/s at 0›C and increases 0.6 m/s for each
degree above zero.
Multiple Reflection of sound :-
 Multiple reflection of sound is the process in which sound waves bounces off
obstacles and reflects many times before reaching the destination. this is the
phenomena that occurs in a stethescope. sound waves reflect through the
tube many times before reaching the ears of the doctor. It is very helpful in
detecting problems.

12.  Reverberation is the persistence of sound in a particular space after
the original sound is removed. A reverberation, or reverb, is created
when a sound is produced in an enclosed space causing a large number
of echoes to build up and then slowly decay as the sound is absorbed by
the walls and air. This is most noticeable when the sound source
stops but the reflections continue, decreasing in amplitude, until they
can no longer be heard. The length of this sound decay, or
reverberation time, receives special consideration in the architectural
design of large chambers, which need to have specific reverberation
times to achieve optimum performance for their intended activity. In
comparison to a distinct echo that is 50 to 100ms after the initial sound,
reverberation is many thousands of echoes that arrive in very quick
succession (.01 – 1 ms between echoes). As time passes, the volume of
the many echoes is reduced until the echoes cannot be heard at all.

13.  In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound,
arriving at the listener some time after the direct sound. Typical examples are the echo
produced by the bottom of a well, by a building, or by the walls of an enclosed room. A true
echo is a single reflection of the sound source. The time delay is the extra distance divided
by the speed of sound.
 Famous Echoes :-
 Gol Gumbaz of Bijapur, India: Any whisper, clap or sound gets echoed repeatedly.
 The Golkonda Fort of Hyderabad, India
 The Whispering Gallery of St Paul's Cathedral, London, England
 Echo Point, the Three Sisters, Katoomba, Australia
 The Temple of Kukulcan ("El Castillo"), Chichen Itza, Mexico
 The Baptistry of Pisa, Pisa, Italy
 The echo near Milan visited by Mark Twain in The Innocents Abroad
 The echo in Chinon which is used in a traditional local rhyme

14.  Hearing range usually describes the range of frequencies that can
be heard by an animal or human, though it can also refer to the
range of levels. In humans the audible range of frequencies is
usually said to be 20 Hz (cycles per second) to 20 kHz (20,000 Hz),
although there is considerable variation between individuals,
especially at the high frequency end, where a gradual decline with
age is considered normal.
Sensitivity also varies a lot with frequency, as shown by equal-
loudness contours, which are normally only measured for research
purposes, or detailed investigation. Routine investigation for
hearing loss usually involvesan audiogram which shows threshold
levels relative to a standardised norm.

15. Species Approximate Range (Hz)
human 64-23,000
dog 67-45,000
cat 45-64,000
cow 23-35,000
rat 200-76,000
bat 2,000-110,000
elephant 16-12,000
goldfish 20-3,000
owl 200-12,000
chicken 125-2,000

16.  Ultrasound is cyclic sound pressure with a frequency greater than the upper limit
of human hearing. Although this limit varies from person to person, it is approximately
20 kilohertz (20,000 hertz) in healthy, young adults and thus, 20 kHz serves as a useful lower
limit in describing ultrasound. The production of ultrasound is used in many different fields,
typically to penetrate a medium and measure the reflection signature or supply focused energy.
The reflection signature can reveal details about the inner structure of the medium, a property
also used by animals such as bats for hunting. The most well known application of ultrasound is
its use in sonography to produce pictures of fetuses in the human womb. There are a vast
number of other applications as well.
 Ability to hear ultrasound
 The upper frequency limit in humans (approximately 20 kHz) is due to limitations of
the middle ear, which acts as a low-pass filter. Ultrasonic hearing can occur if ultrasound is fed
directly into the skull bone and reaches the cochlea through bone conduction without passing
through the middle ear.
 It is a fact in psychoacoustics that children can hear some high-pitched sounds that older
adults cannot hear, because in humans the upper limit pitch of hearing tends to become
lower with age. A cell phone company has used this to create ring signals supposedly only able
to be heard by younger humans; but many older people are able to hear it, which may be due
to the considerable variation of age-related deterioration in the upper hearing threshold.
 Some animals — such as dogs, cats, dolphins, bats, and mice — have an upper frequency limit
that is greater than that of the human ear and thus can hear ultrasound, which is how a dog
whistle works.

17.  Sonar (originally an acronym for SOund Navigation And Ranging) is a
technique that uses sound propagation (usually underwater, as in Submarine
navigation) to navigate, communicate with or detect other vessels. Two types
of technology share the name "sonar": passive sonar is essentially listening for
the sound made by vessels; active sonar is emitting pulses of sounds and
listening for echoes. Sonar may be used as a means of acoustic locationand of
measurement of the echo characteristics of "targets" in the water. Acoustic
location in air was used before the introduction of radar. Sonar may also be
used in air for robot navigation, and SODAR(an upward looking in-air sonar)
is used for atmospheric investigations. The term sonar is also used for the
equipment used to generate and receive the sound. The acoustic frequencies
used in sonar systems vary from very low (infrasonic) to extremely high
(ultrasonic). The study of underwater sound is known as underwater
acoustics or hydroacoustics.

18.  The ear is the anatomical organ that detects sound. It not only acts as a
receiver for sound, but also plays a major role in the sense of balance and
body position. The ear is part of the auditory system.
 The word "ear" may be used correctly to describe the entire organ or just
the visible portion. In most mammals, the visible ear is a flap of tissue that
is also called the pinna and is the first of many steps in hearing. In people,
the pinna is often called the auricle. Vertebrates have a pair of ears, placed
symmetrically on opposite sides of the face. This arrangement aids in the
ability to localize sound sources.
 Introduction to ears and hearing
 Audition is the scientific name for the sense of sound. Sound is a form of
energy that moves through air, water, and other matter, in waves of
pressure. Sound is the means of auditory communication, including frog
calls, bird songs and spoken language. Although the ear is the vertebrate sense
organ that recognizes sound, it is the brain and central nervous system that
"hears". Sound waves are perceived by the brain through the firing of nerve cells in
the auditory portion of the central nervous system. The ear changes sound
pressure waves from the outside world into a signal of nerve impulses sent to the
brain.

19.  Sounds are generally audible to the human ear if their frequency (number of
vibrations per second) lies between 20 and 20,000 vibrations per second (Hertz),
but the range varies considerably with the individual. Sound waves with
frequencies less than those of audible waves are called subsonic; those with
frequencies above the audible range are called ultrasonic.
 Sound waves can be reflected, refracted (or bent), and absorbed as light waves
can be. The reflection of sound waves can result in an echo—an important factor
in the acoustics of theaters and auditoriums. A sound wave can be reinforced with
waves from a body having the same frequency of vibration, but the combination
of waves of different frequencies of vibration may produce “beats” or pulsations or
may result in other forms of interference.

20.  Sound is nothing but waves travelling with different frequency,
wave length and pitch. As to humans sound of particular frequency is
Hearable that is 20Hz to 20,000 Hz. This frequency is expressed in
hertz (Hz). We can measure the sound in many ways the simplest
way is with an output meter. The three most important properties for
audio work are wavelength ,amplitude , frequency. Reverberation is
the persistence of sound in a particular space after the original sound
is removed. Echo is the reflection of sound sometime after hearing
the original sound . It can be heard in an empty room.