Introduction to Audiography/Sound

The Presentation explain the fundamentals of audio/sound. The Syllabus followed in this ppt is from Nehru Arts and Science College, Coimbatore.

1. PREPARED BY
SANKARANARAYANAN. K. B
ASST. PROFESSOR
DEPARTMENT OF VISUAL COMMUNICATION
NEHRU ARTS AND SCIENCE COLLEGE
COIMBATORE
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2. Course Code
Title
19U3VCC306
Core Paper VI
Audiography
Semester: IIICredits: 4 CIA : 25 Marks ESE : 75 Marks
Instructional
Objective:
To demonstrate a basic professional level of accomplishment in the core areas of audio technology
including: non-linear digital audio recording and editing, sound design for music and film/ video, and the
mixing and mastering of audio projects.
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3. UNIT -1
Topic to be covered Expected Outcomes
Perceptionofsound-Nature-Characteristicsof
soundwave:-Transverseandlongitudinalwave
Students can understands the basics of physics
and fundamental of Audiography.
Behaviorofsoundinvariousstates.Amplitudes,
Frequency,Velocity,Wavelength,Phase,
Harmonics,Octaves,overtoneandtimbre
Psychoacoustics-Dynamicrange-Noise.
Theartofhearingandauditoryperception
Structureofear,Thresholdofpainandhearing-
Loudness.
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4. Theearhasanenormousrangeofresponse,
bothinfrequencyandinintensity.The
frequencyrangeofhumanhearingextends
overthreeordersofmagnitude,fromabout
20hertztoabout20,000hertz,or20
kilohertz.
IMPORTANT POINT TO REMEMBER
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5. 1) SOUND
Soundisproducedduetothevibrationofobjectsormoleculesin
theatmosphere.Sound,amechanicaldisturbancefromastateof
equilibriumthatpropagatesthroughanelasticmaterialmedium.
E.g.:-thesoundofhumanvoiceisproducedduetothevibrationof
thevocalcords.Astretchedrubberbandwhenpluckedvibratesand
producessound.
Thread
tuning fork
Table tennis
ball
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6. 2) SOUND NEEDS A MEDIUM TO TRAVEL
Soundisamechanicalwaveandneedsa
mediumforpropagation.Soundtravels
throughsolids,liquidsandgases.Sounddoes
nottravelinvacuum.
Bell jar Electric bell
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7. Propagation of sound through air :-
Airisthemostcommonmediumthroughwhichsoundtravels.Whena
vibratingobjectmovesforward,itpushesandcompressestheairinfrontofit
formingaregionofhighpressurecalledcompression(C).Thecompression
movesawayfromthevibratingobject.Whenthevibratingobjectmoves
backward,itformsaregionoflowpressurecalledrarefaction(R).Asthe
objectmovestoandfrorapidly,itproducesaseriesofcompressionsand
rarefactionintheairwhichmakesthesoundtopropagateinthemedium.
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8. 3) PROPAGATION OF SOUND
Thesoundproducedbyavibratingobjecttravelsthroughamedium
toalistener.Themediumcanbesolid,liquidorgas.
Whenanobjectvibrates,theparticlesaroundthemediumvibrates.
Theparticleincontactwiththevibratingobjectisfirstdisplacedfrom
itsequilibriumposition.Itthenexertsaforceontheadjacentparticle
andtheadjacentparticleisdisplacedfromitspositionofrest.After
displacingtheadjacentparticlethefirstparticlecomesbacktoits
originalposition.Thisprocessrepeatsinthemediumtillthesound
reachestheear.
Thedisturbanceproducedbythevibratingbodytravelsthroughthe
mediumbuttheparticlesdonotmoveforwardthemselves.
Awaveisadisturbancewhichmovesthroughamediumbythe
vibrationoftheparticlesofthemedium.Sosoundisconsideredasa
wave.Sincesoundwavesareproducedduetothevibrationofparticles
ofthemediumsoundwavesarecalledmechanicalwaves.
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9. Compression Rarefraction
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10. 4) SOUND WAVES ARE LONGITUDINAL
Sound propagates in a medium as a series of compressions (C) and
rarefactions (R).
In these waves the particles move back and forth parallel to the direction of
propagation of the disturbance. Such waves are called longitudinal waves.
There is another kind of waves called transverse waves. In these waves the
particles oscillate up and down perpendicular to the propagation of the
direction of disturbance.
C C CR R R
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11. 5) CHARACTERISTICS OF A SOUND WAVE
Soundwavecanbedescribedbyitsfrequency,amplitudeandspeed.
Soundcanbegraphicallyrepresentedasawave.Thereischangesinthe
densityandpressureassoundmovesinamedium.
Compressionsaretheregionsofhighpressureanddensitywherethe
particlesarecrowdedandarerepresentedbytheupperportionofthecurve
calledcrest.
Rarefactionsaretheregionsoflowpressureanddensitywherethe
particlesarespreadoutandarerepresentedbythelowerportionofthe
curvecalledtrough.
Thedistancebetweentwoconsecutivecompressions(crests)ortwo
consecutivetroughsiscalledwavelength.Itisrepresentedbythesymbol.
(greekletterlamda).ItsSIunitismetre(m).
compression rarefaction
Pressure or Density
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12. 6) FREQUENCY OF SOUND WAVE
Whensoundispropagatedthroughamedium,thedensityofthe
mediumoscillatesbetweenamaximumvalueandaminimumvalue.
Thechangeinthedensityofthemediumfromamaximumvaluetoa
minimumvalueandagaintothemaximumvalueisoneoscillation.
Thenumberofoscillationsperunittimeiscalledthefrequencyof
thesoundwave.
Itisrepresentedbythesymbol٧(greekletternu).
Itssiunitishertz(hz).
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13. 7) AMPLITUDE OF SOUND WAVE
THEMAGNITUDE OFTHEMAXIMUM DISTURBANCE
INTHEMEDIUMONEITHERSIDEOFTHEMEANVALUE
ISTHEAMPLITUDEOFTHESOUNDWAVE.
Wave disturbance
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14. ENVELOPE
•The envelope is a form of automation (automatic movement) built into synthesizers
to control the value of a parameter (usually volume or filter cutoff frequency) over
time. Envelopes are critical for giving synthesizers a more natural and interesting
sound, as they can be used to simulate the volume envelopes of a real instrument.
However, envelopes are also great for creating special effects. The most common
type of envelope is called ADSR (Attack, Decay, Sustain, Release), referring to the
different functions of each part of the envelope.
•Attack -The time it takes for the note to reach the maximum level.
•Decay-The time it takes for the note to go from the maximum level to the sustain
level (the next level in the ADSR chain).
•Sustain-The level while the note is held.
•Release-The time it takes for the note to fall from the sustain level to zero (silence)
when released.
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15. 8) LOUDNESS
Theloudnessofsounddependsupontheamplitudeofvibration.
Iftheamplitudeisbigger,thesoundisloudandiftheamplitudeissmaller,the
soundissoft.
Amplitude is Loudness
The size of a wave (how much it is "piled up" at the high points) is its amplitude. For
sound waves, the bigger the amplitude, the louder the sound.
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16. 9) PITCH & HARMONICS
Thepitchofsound(shrillnessorflatness)dependsonthe
frequencyofvibration.
Ifthefrequencyishigh,thesoundhashighpitchandifthe
frequencyislow,thesoundhaslowpitch.
Aharmonicofsuchawaveisawavewithafrequencythatisa
positiveintegermultipleofthefrequencyoftheoriginalwave,
knownasthefundamentalfrequency.Theoriginalwaveisalso
calledthe1stharmonic,thefollowingharmonicsareknownas
higherharmonics.
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17. TIME PERIOD OF SOUND WAVE
Thetimetakenforthechangeinthedensityofthemedium
fromamaximumvaluetoaminimumvalueandagaintothe
maximumvalueisthetimeperiodofthesoundwave.
Or
Thetimetakenforonecompleteoscillationinthedensity
ofthemediumiscalledthetimeperiodofthesoundwave.
Itisrepresentedbythelettert.
Thesiunitissecond(s).
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18. 10) SPEED OF SOUND
Thespeedofsoundisdifferentin
differentmedium.Thevelocityofsoundis
moreinsolids,lessinliquidsandleastin
gases.
Theswiftnessofsoundalsodependson
thetemperatureofthemedium.Ifthe
temperatureofthemediumismore,the
speedofsoundismore.
Speed of sound in different
media at 25
0
c.
Relationship between Speed (v), frequency
(٧) and wave length (Λ)
Speed = wavelength * Frequency
V = λx ٧
State Substance Speed in m/s
Solid
Aluminium 6420
Steel 5960
Iron 5950
Brass 4700
Glass 3980
Liquid
Water (sea) 1531
Water (distilled) 1498
Ethanol 1207
Methanol 1103
Gas
Hydrogen 1284
Helium 965
Air 343
Oxygen 316
Sulphurdioxide 213
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19. 11) REFLECTION OF SOUND
Likelight,soundgetsreflectedatthesurfaceofasolid
orliquidandfollowsthelawsofreflection.
I)theangleofincidenceisequaltotheangleof
reflection.
Ii)theincidentray,thereflectedrayandnormalatthe
pointofincidencealllieinthesameplane.
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20. 12) ECHO
If we shout or clap near a reflecting surface like tall building or
a mountain, we hear the same sound again. This sound which we
hear is called echo. It is caused due to the reflection of sound.
To hear an echo clearly, the time interval between the original
sound and the echo must be at least 0.1 s.
Since the speed of sound in air is 343 m/s, the distance travelled
by sound in 0.I s = 343 m/s x 0.1 s = 34.3m
So to hear an echo clearly, the minimum distance of the
reflecting surface should be half this distance, that is 17.1 m.
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21. B) REVERBERATION
•B) Reverberation:-
• Echoes may be heard more than once due to repeated or multiple
reflections of sound from several reflecting surfaces. This causes
persistence of sound called reverberation.
• In big halls or auditoriums to reduce reverberation, the roofs and
walls are covered by sound absorbing materials like compressed fibred
boards, rough plaster or draperies.
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22. 13) USES OF MULTIPLE
REFLECTION OF SOUND :-
I)Megaphones,horns,musicalinstrumentsliketrumpets,shehnais
etc.Aredeignedtosendsoundbymultiplereflectioninaparticular
directionwithoutspreadinginalldirections.
Ii)Doctorslistentosoundsfromthehumanbodythrougha
stethoscope.Thesoundofheartbeatreachesthedoctor’searsby
multiplereflection.
Iii)Generallytheceilingsofcinemahallsandauditoriumsarecurved
sothatsoundaftermultiplereflectionreachesallpartsofthehall.
Sometimesacurvedsoundboardisplacedbehindthestagesothat
soundaftermultiplereflectionspreadsevenlyacrossthehall.
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23. 14) RANGE OF HEARING
•Humanbeingscanhearsoundfrequenciesbetween20hzand
20000hz.
•Soundwhosefrequencyislessthan20hziscalledinfrasonic
sound.Animalslikedogs,elephants,rhinoceros,whalesetc.
Produceandhearinfrasonicsound.
•Soundwhosefrequencyismorethan20000hziscalled
ultrasonicsound.Animalslikedolphins,bats,ratetc.Produceand
hearultrasonicsound.
dB
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24. 15) USES OF ULTRASONIC SOUND
I)Ultrasonicsoundisusedtocleanobjectslikeelectroniccomponents.Due
tothehighfrequency,thedirtparticlesgetdetachedfromthecomponents.
Ii)Ultrasonicsoundisusedtodetectcracksinmetalblocks.Ultrasonicwaves
aresentthroughthemetalblocksandiftherearecracks,thewavesare
reflectedbackandthecrackscanbedetected.
Iii)Ultrasonicsoundisusedinultrasoundscannersforgettingimagesof
internalorgansofthehumanbody.
Iv)Ultrasonicsoundisusedtobreaksmallstonesformedinthekidneysinto
finegrainssothattheyareremovedthroughtheurine.
V)Batsusereflectionofultrasonicsoundwavestodetectanobstacleorits
prey.
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25. 16) SONAR
Sonarstandsforsoundnavigationandranging.Itisadevice
whichusesultrasonicwavestomeasuredistance,directionand
speedofunderwaterobjects.
Sonarhasatransmitterandadetectorinstalledinships.The
transmitterproducesultrasonicsoundwaveswhichtravel
throughthewaterandafterstrikingtheobjectintheseabedis
reflectedbacktothedetector.
Thedistanceoftheobjectcanbecalculatedbyknowingthe
speedofsoundinwaterandthetimetakenbetweenthe
transmissionandreceptionofultrasound.
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26. 17) STRUCTURE OF THE HUMAN EAR
Theouterearcalledpinnacollectsthesoundwaves.Thesoundwavespasses
throughtheearcanaltoathinmembranecalledeardrum.Theeardrumvibrates.The
vibrationsareamplifiedbythethreebonesofthemiddleearcalledhammer,anviland
stirrup.Themiddleearthentransmitsthesoundwavestotheinnerear.Intheinner
earthesoundwavesareconvertedintoelectricalsignalsbythecochleaandsenttothe
brainthroughtheauditorynerves.Thebraintheninterpretsthesignalsassound.
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27. PSYCHOACOUSTICS
•Itisthescientificstudyofsoundperceptionandaudiology.More
specifically,itisthebranchofsciencestudyingthepsychologicaland
physiologicalresponsesassociatedwithsound(includingnoise,speechand
music).Itcanbefurthercategorizedasabranchofpsychophysics.
Psychoacousticsreceiveditsnamefromafieldwithinpsychology—i.e.,
recognitionscience—whichdealswithallkindsofhumanperceptions.Itis
aninterdisciplinaryfieldofmanyareas,includingpsychology,acoustics,
electronicengineering,physics,biology,physiology,andcomputerscience.
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28. TOPICS COVERED
•Basics of sound
•Frequency, Wavelength, Amplitude, Envelope, Time Period
•Loudness and human hearing range, Echo & Reverb
•Longitudinal and transverse waves
•Ultrasonic and infrasonic
•Sonar and Structure of Ear
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29. SUMMARY
•Soundisamechanicalvibrationcausedduetothevibrationof
objectsonmoleculesinamedium(Solid/Liquid/Gas).It’saperceived
sensationbyourEarandbraintogether.Thecharacteristicsofsound
areitsfrequency,wavelength,amplitude,speed,timeperiod,
loudnessandenvelope.ThereflectivepropertyofSoundisusedfor
manyapplicationslikeUltrasoundscanning,Sonar,Cleaningof
electronicInstrumentsetc.Thestructureofearhelpstodetectthe
distanceandpositionofsound.Phsychoacousticsissaidtobethe
sciencethatdealswiththestudyofaudiologyandsoundperception.
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30. REFERENCE BOOK/WEB-LINK/E-CONTENT
•Ronald.Mc.Donald, Home recording handbook, Frame
trees publications ,2004.
•modern-recording-techniques-seventh-edition-book.pdf
•https://www.youtube.com/watch?v=uJDDI9beju4
•https://www.youtube.com/watch?v=rkwS6vigSyE
•https://www.youtube.com/watch?v=ZbUTyMC8_X8
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31. THANK YOU
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