BASICS OF AUDIO & VIDEO MEDIA IV Sem_Module 1.pdf

Basics of Audio Video Media

1. BASICS OF AUDIO &
VIDEO MEDIA
MODULE I
CHARACTERISTICS OF SOUND AND ACOUSTICS

2. WHAT IS SOUND?

3. WHAT IS SOUND?
Sound in Physics
Sound is defined as the vibration that results in an easy to hear mechanical
wave that proceeds on pressure and displacement using medium as air or
water to propagate itself.

4. WHAT IS SOUND?
Sound in Psychology
Sound is what brain recognizes as a result of the auditory sensation evoked
by the reception of propagated waves, by the hearing senses of living
organisms.

5. ORIGINATING SOUND
•Sound source?
•Sound wave?
•Propagating medium?
•Pressure, Velocity and Displacement

6. SPEED OF SOUND
•Temperature of the medium affects the relationship between density and
pressure, which increases the speedof sound in that medium. If the
medium itself is in motion (wind), it further speeds up.
•Viscosity of the medium affects the motion of sound waves through the
medium and thus reduces the speed of sound.
•
Sound cannot be propagated in Vacuum.

7. ACOUSTICS
•The study of mechanical waves in media such as in solid, liquid and gas
including aspects of vibration, sound, ultrasound and infrasound.
Acoustics applications are used in most fields that deal with control of
audio and noise. The term Acoustics is Greek and Latin synonym is
“Sonic”
•Ultrasonic & Infrasonic -Frequencies above and below human audible
range.

8. ACOUSTIC OCCURENCE
Cause
Generating
Mechanism
(Transduction)
Acoustic wave
propagation
Reception
(transduction)
Effect
Natural or
Volitional
Source
Conversion
to Sonic
Energy
Energy carried
by Acoustic
wave
Converted
back, Natural
or Volitional
Perception
of Sound

9. SPEECH, MUSIC & NOISE

10. SPEECH
•Speech is not a constant sound, it is highly variable and momentary. Speech
is more of passing energy between the three dimensions of Frequency,
Sound level and Time.
•Spectrogramis used to depict sound in three dimensions.
•Coughing, crying, snoring and laughing are examples for other sounds that
human can produce.

11. SOURCES OF SPEECH
•VOICED SOUNDS: Sounds that proceeded from vocal cords. Air moves
from lungs to the glottis (slit between vocal cords) and makes vibration,
which makes sound.
•FRICATIVE SOUNDS: Sounds made by using teeth, tongue or lips. The
forced air and controlled pressure produces turbulence which creates sounds
like f, s, v and z.
•PLOSIVE SOUNDS: Holding the breath and building pressure, the sudden
release of breath makes sounds make sounds like k, p and t.

12. VOICED & NON- VOICED SOUNDS
•Voiced sounds are produced by the vibrations in the vocal cord and travels
through vocal tract.
•Non-voiced sounds are usually referred as the sounds produced without the
vibration of vocal cords, that is fricative sounds.

13. SYTHESIZED SPEECH - History
•Speech that originates from mechanical speaking devices is termed as
Synthesized Speech.
•Invention of Wolfgang von Kempelenin 1791 led to the development of
Synthesized Speech Machines.
•In 1876, Alexander Graham Bell patented the procedure for producing
speech based on Kempelen’smachine.
•In 1939,Voder developed more simple analogue machine for recognizable
speech.

14. SYTHESIZED SPEECH - Today
•Language translators
•Blind audio assistants
•Talking clock and calculators
•Computer based speech recognition systems
•Audio filters for modulating sounds in audio editing
•Digitized speech

15. MUSIC
•It seems to identify the musical pattern of a single instrument where it seems
difficult when a music band comprises of a number of musical instruments
altogether. The complexity comes as the tonal characteristics of each
instruments differ, as in the difference between different speech sounds.

16. MUSICAL INSTRUMENTS
•STRING INSTRUMENTS: Tones are produced by vibration of stretched
strings like violin, sitar and guitar. Shape of instrument, size of instrument,
type of material used for the instrument, varnish or paint over the
instrument body can effect the overtone of the instrument.
•WIND INSTRUMENTS: Wind instruments produce sound by the
resonance of air in pipes or tubes. Where the length of the column is
constantly changed to produce a pattern. Trumpet, Flute and Saxophone are
examples.

17. HARMONIC & NON HARMONIC MUSIC
•Most of the musical instruments give harmonic music which makes the
music attractive and gives it a specific pattern. But there are instruments that
are non- harmonic. Musical instruments like Tabla, Piano overtunes, Drum
and bands doesn’t provide harmonic sounds. These instruments but always
blend with the harmonic sounds of other instruments.
•Eg: Bell.

18. DYNAMIC RANGE OF MUSIC
•Dynamic Range of music, also speech, is referred as the distance between
the loudest sound and the softest note in terms of dB, which can be
experienced at a concert hall.
•Conventional media doesn’t have the capability of handling the full dynamic
range as it may cause noise at lower tones and distortion at upper tones.
•Advent of digital media enables to relate a range of binary digits to the
dynamic range such as 4=24, 8=48, 12=72, 16=96, 24=144.

19. POWER OF MUSIC
•The peak power of different sound sources are important in sound studies.
Power of human speech is around 10 microwatts to a peak of 1 milliwatts .
The peak power of few instruments are:
•Full Orchestra: 70 Watts
•Large Bass drum: 25 Watts
•Piano: 0.4 Watts
•Flute: 0.06 Watts

20. AUDITORY AREA
•Human Ear has a complex auditory area enables to hear wide range of
frequencies and dynamic ranges. A small portion of auditory area is used for
speech having average dynamic range of 42dB and 170- 4000Hz. For music,
the auditory area having average dynamic range of 75dB and frequency range
between 50- 8500Hz.

21. NOISE
•Hmm
•Yay!
•Ohh!
•Booooom!
•Shhhh!
•Trrrr!
•Rain
•Sound of Fan
•Music Orchestra
•Sound of a train
•Hiss sound of radio
•Crowd noise

22. ACCEPTABLE AND RANDOM NOISE
•NOISE IS SIMPLY UNDESIRABLE SOUNDS.
•ACCEPTABLE NOISE: Acceptable noise is referred as the noise that are
found useful according to the contexts. The narrow band of noise would be
useful in a studio to check the output level instead of trying with highly
variable vocals.
•
RANDOM NOISE: The noise produced by electric circuits are termed as
Random Noise. Thermionic tubes, silicon diodes and other solid state devices generate Random Noise.

23. WHITE AND PINK NOISE
•WHITE NOISE: Similar to white light, white noise have uniform
distribution of energy.
•PINK NOISE: The noise that has a higher frequency in the lower frequency
region, that is, noise in the lower frequency range that exhibits high energy
levels.

24. SIGNAL DISTORTION
•Signal distortion is the change in the sound when it is passed through various signal
processing gears. Digital signal distortion is used to reduce noise in digital audio
editing process.
•BANDWIDTH LIMITATION
•NON-UNIFORM RESPONSE
•DISTORTIONS IN TIME
•PHASE DISTORTIONS
•CROSSOVER DISTORTION
•HARMONIC DISTORTION

25. MECHANISM OF HEARING OF HUMAN EAR

26. PSYCHOACOUSTICS
•The study of the physical structure of human ear comes under Physiology, but the
process of perception of sound by human ear comes under Psychology and
Psychoacoustics.
•Psychoacousticsis a branch of sound science that deals with the study of
•The physical structure of ear,
•The sound pathways and their function
•The human perception of sound
•The interrelationships between these

27. ANATOMY OF EAR
Outer Ear: Includes the pinna and the
auditory canal that terminates at the
tympanic membrane/ear drum
Middle Ear: Cavity filled with air, three
bones –malleus, incus and stapes bridges
the cavity. Malleus connects to ear drum
where stapes attached to oval window.
These bones act as mechanical lever.
Inner Ear: extends till the auditory nerve,
sending impulses
Eustachian Tube*

28. PARTS OF EAR
•PINNA
•EAR CANAL
•MIDDLE EAR
•INNER EAR
•COCHLEA
•STEREOCILIA
•AUDITORY CORTEX -BRAIN

29. EAR –AN ANALYZER &
MEASURING INSTRUMENT
•Distinguishing different sounds
•Distinguishing instruments
•
Selective Perception

30. LOUDNESS & FREQUENCY
•What is LOUDNESS? Phons
•What is FREQUENCY? Hz
•What is SOUND-PRESSURE LEVEL dB
Frequency and Sound-pressure level can greatly influence perceived loudness. A
frequency of 1000Hz and sound-pressure level of 30dB produces a loudness level of
30 Phons. With frequency of 20Hz and additional sound-pressure of 58dB also can
produce the same loudness.
•Loudness Control

31. PITCH & FREQUENCY
•What is PITCH? Sensation of a Frequency
•What is FREQUENCY? Number of waves per sec.
Female Sound (165-255 Hz) Male sound (85-180 Hz)

32. TIMBRE AND SPECTRUM
•What is TIMBRE? Harmonics
•What is SPECTRUM? Analogue term

33. PRECEDENCE EFFECT
•Precedence Effect is the capability of human ear mechanism to recognize
the original source of sound when there is a number of reflections of the
same sound.

34. CONCEPT OF STEREOPHONY
•Stereophony, a term used in Audio Recording, is the concept of recording
sound with a dual pickup providing a right and a left channel. It is also called
multi-track, multichannel or separation recording.
•Monophonic recording involves merging the outputs of a several
microphones by summing network and recording on a single- track tape.
•Stereophonic recording use a set of microphones and the output of each
microphone is recorded on a separate track of the tape. Later in a mix down
session, the signals of the several tracks are combined.

35. CONCEPT OF STEREOPHONY
Single
Track
Recroder
Multi-
Track
Recroder
Microphones (R)
Microphones (R)
Microphones (L)
Microphones (L)

36. PROS AND CONS OF MULTI-TRACK
Advantages Disadvantages
Flexibilityin Editing Noiseaccording to the number of channels
Surrounding Effectcan be produced Combined dynamic range system
Can be converted to mono or stereolaterDistance of micsand crosstalk
Lesserchances for errors while recording
Special effect can be applied for each track
Retakesof particular performer found easy
Multiple instruments withvarious settings
Lesser noise for different gain levels

37. AUTOMATION IN AUDIO RECORDING
•Digital Audio consoles
•Automated audio editing tools and software
•Presets in consoles
•Presets in software
•Automation in Audio Broadcast

38. NATURE AND PROPERTIES OF SOUND
•Reflection
•Refraction
•Diffraction

39. REFLECTION
•Changes in the straight line path of a sound wave due to any obstacles in the
surroundings. An open space doesn’t cause any reflection where a room,
different objects in the room, walls, roof etc. cause different levels of
reflections.

40. REFLECTION ON FLAT SURFACES

41. REFLECTION INSIDE A CYLINDER

42. CORNER REFLECTION

43. REFLECTION ON
CONCAVE/CONVEX/PARABOLA
•Depending on the size of the reflector surface, the amount of reflection
vary. Convex surfaces offer a higher amount of reflection where the concave
surfaces offer lesser reflection

44. STANDING WAVE
•The two sound sources positioned towards opposite directions between two
solid walls. The first sound from source 1 can hit right wall and reflect where
the second sound from source 2 hits left wall and reflect. The meeting point
of two waves while reflection is termed as Standing wave as it is static at the
point.

45. REFLECTION ON
CONCAVE/CONVEX/PARABOLA
•Depending on the size of the reflector surface, the amount of reflection
vary. Convex surfaces offer a higher amount of reflection where the concave
surfaces offer lesser reflection

46. IMPEDANCE IRREGULARITIES
•When the propagating medium remains the same and the setting of the
medium changes suddenly causes Impedance Irregularities.
•Eg: Air conditioner duct.

47. ECHO
•Echo happens when the sound is reflected back to the sound source.
Depending on the reflection surface, the level of echo changes.

48. REFRACTION

49. REFRACTION IN DIFFERENT MEDIA
•ATMOSPHERE –Temperature, Wind
•OCEAN –Temperature, Density and Pressure
•ENCLOSED SPACES -Temperature

50. FACTORS THAT AFFECT REFRACTION
•Angle of wave when it enters to a new medium
•Velocities of wave in the old and new medium
•Density of the two media
•Temperature in the two media

51. DIFFRACTION
•The process of scattering the sound waves while it travels in a straight line
path. It enables the sound to be heard in the surrounding, similar to the
scattering of light rays.

52. DIFFRACTION ON
DIFFERENT OBJECTS
•Human Head
•
Loudspeaker cabinet edges

53. SOUND ABSORPTION
•According to the law of conservation of energy, energy can neither be
created nor destroyed but can be changed from one form to another.

54. DISSIPATION OF SOUND ENERGY
WallWallAcoustic
Material
Heat

55. EVALUATION OF SOUND ABSORBTION
•Reverberation Chamber Method (Reverberation room and absorption
material)
•Impedance Tube Method (Tube and absorption material)
•
Tone-Burst Method (Receptor replaced by absorption material)

56. QUALITIES OF ABSORPTION MATERIAL
•Density
•Thickness
•Airspace
•Placement of material
•Eg: Boards, foams, fabrics, carpets and cushions
•Human absorption

57. ACOUSTICS FOR SOUND STUDIO
•Direct sound and Indirect sound
•Studio response
•Factors of studio response: Surfaces of the room, room resonance,
materials/objects in the room etc.

58. REVERBERATION
•The combined average effect of studio response is called reverberation.
•Reverberation time can be used to identify the amount of absorbent needed
to improve the acoustical quality of the studio.

59. STUDIO DESIGN
•Room volume
•Room proportions
•Sound decay rate
•Diffusion and Isolation from noise

60. STUDIO DESIGN
•Room volume
•Room proportions
•Sound decay rate
•Diffusion and Isolation from noise

61. ACOUSTICS OF AUDITORIUM
•Avoiding strong echoes ( Make use of scatterers, convex surfaces on balcony
fronts, absorption material on concave and flat surfaces, carpets and echo-
free furnitures/seats.
•Intimacy (Gap between original sound and first reflection)
•Clarity (Sound level of the source should be higher that that of background
sound)
•Reduction of External noises

62. GROWTH AND DECAY OF SOUND
•Enclosures
•Acoustic Material

63. ACOUSTIC EFFECTS
THAT SHOULD BE AVOIDED
•Echoes
•Loudness
•Flutter
•Excessive/Selective absorption
•
Dead spots

64. ENCLOSURE DESIGN
•Rectangular Hall
•Fan shaped hall
•Horse- shoe shaped hall