Unit 1: Introduction to Sound I
1. What are are the primary primary factors factors aecting aecting the speed speed of sound in air? Absolute temperature Molecular Mass of the gas 2. Briey dene each each of the folloing folloing a!e a!e characteristics" characteristics" and gi!e an appropriate unit of measure# a. Amplitu itude Ma$imum sound pressure %&ascals' b. (eloci locity ty )istance*+ime %metres*second' c. ,re-u e-uency ncy umber of !ibrations per second %/ert0' d. Wa!el a!elen engt gth h )istance beteen any to corresponding points %metres' e. &hase Where the graph begins on the $a$is % degrees or seconds' 3. Briey Briey distinguis distinguish h beteen beteen dB456" dB456" dB&W6" dB&W6" 7 dB4&6. dB4&6. dBSIL 8 4ound 5ntesity 6e!el is the o of energy through a units area I actual 10log 10 I ref • •
•
•
•
•
•
•
•
•
here 5 actual is the actual sound poer density le!el %in W m 2' here 5 ref is the reference sound poer le!el %19 12 W m2' dBPWL(SWL) 8 4ound &oer 6e!el is the total poer radiated in all directions by a source W actual 10log 10 W ref here W actual is the actual sound poer density le!el %in W' here W ref is the reference sound poer le!el %19 12 W' dBSPL 8 4ound &ressure 6e!el is a ay of measuring and describing the amplitude of a sound a!e at a particular point P actual 20log 10 P ref here & actual is the actual sound poer density le!el %in &a' here & ref ref is the reference reference sound poer le!el %29 : 19 ; &a < 29 =&a'
Unit 2: Introduction to Sound II
1. What is the result result of combining to identical sine a!es ith ith a relati!e relati!e phase dierence of 1>9 degrees? 9 2. With regard regard to the beha!iour beha!iour of of a!es" a!es" briey dene each each of the the folloing folloing terms# a. 4upe 4uperp rpos osit itio ion n Wa!es may pass through each other transparently b. )ir iractio ction n Wa!es may bend around obects •
•
•
c. @efraction Wa!es may change direction due to changing !elocity d. Absorption Wa!e energy may be con!erted to !ibration or lost to friction e. @eection 4ound is reected hen it hits a physical obect o Angle of incidence < angle of reection o +ype 1# 4triing an immo!able obect*hard boundary o +ype 2# Bounded to unbounded f. )iusion Wa!es may scatter into multiple loer energy traectories 3. /o does the addition of correlated sounds dier from the addition of uncorrelated sounds? orrelated sound sources# o 4imply add pressures a!es together Cncorrelated sound sources# o Add the s-uares of the pressure a!es together and then s-uare root the result Cse this e-uation to nd the pressure !alues hen gi!en dB !alues to or out total dB# •
•
•
•
•
•
•
P
2
=
10
SPL 10
2
×Pref
Where &ref 2 ould be e-ual to D : 19 19 D. Why are sounds softer further aay from their source? +he energy in the sound a!e is spread more and more thinly as the a!efront e$pands. E. What is meant by Facoustic impedanceF? @atio of acoustic pressure to o %in !s out' almost lie resistance ;. What is meant by dBA and dB" and hen is each appropriate to use? dBA Aeighting is applied to instrumentmeasured sound le!els in eort to account for the relati!e loudness percei!ed by the human ear" as the ear is less sensiti!e to lo audio fre-uencies %C@(G' Cse for orplace. db 8 eighting follos the fre-uency sensiti!ity of the human ear at !ery hiHgh noise le!els %,6A++G@ C@(G' Cse for house parties" here bass is craned up. I. What is the eect of mounting a loudspeaer in the corner of a room up against the ceiling? Jutput is K dB more than if mounted in free space >. Are four trombones tice as loud as to trombones? G$plain your anser. Are tenty clarinets tice as loud as to clarinets? G$plain your anser. o" D trombones are not nearly tice as loud as 2 trombones. +he same goes for the 29 clarinets !s 2 clarinets o +he doubling of instruments results in an addition of appro$imately 3dB for each doubling o +he further aay the sound is" by the doubling of metres" loss of appro$imately ;dB for each doubling •
•
•
•
•
•
K. A single (u!u0ela is measured as producing a sound pressure le!el of K2 dB4&6 at some arbitrary point in front of the player. onsidering that 2919 stadiums hold beteen E9"999 and 199"999 spectators" hat ould be the cumulati!e 4&6 produced if e!ery one of 199"999 spectators ere to blo at the same time? /o about if only an eighth of all 199"999 spectators ere to be playing simultaneously? +o simplify you may assume that all (u!u0elas are being played from the same seat %disregard attenuation o!er distance'. 199999" closest 2 poer is 1319I2%2 1I' o +herefore appro$imate cumulati!e 4&6 ill be K2 H 3%1I' < 1D3dB4&6 Gighth of 199999 < 12E99" closest 2 poer is 1;3>D%2 1D' o +herefore appro$imate cumulati!e 4&6 ill be K2 H 3%1D' < 13DdB4&6 C4G 6JL4 ,J@ MJ@G AC@AN •
•
•
Unit 3: Introduction to Sound III
1. Li!e e$amples %in /ert0' of each of the folloing# a. A ObassP fre-uency Belo ;9/0 b. A OmidP fre-uency Beteen ;9/0 and >/0 %>999/0' c. A OhighP fre-uency Lreater than >/Q %>999/0' d. A fre-uency commonly used for tuning orchestral instruments DD9/0 %A abo!e middle ' e. +he fre-uency of Omiddle P 2;1/0 2. /o ould you describe the range of fre-uencies beteen K9 /ert0 and 2E9 /ert0? Midrange fre-uency 3. What is ,ourierRs +heorem" and hat does it mean for music? 5t allos one to brea a comple$ a!e into many simple a!es 5t pro!ides a means of translating beteen the time and fre-uency domains 5t allos one to determine hich fre-uencies are present in a gi!en sound %,undamental can be used to determine pitch' D. Briey e$plain hy spectral analysis is ine!itably a tradeo beteen fre-uency and time resolution. ,ilters# o 6opass &asses fre-uencies belo the cuto o /ighpass &asses fre-uencies abo!e the cuto o Bandpass &asses fre-uencies beteen to cutos o Bandreect &asses fre-uencies that are not beteen to cutos E. What is the essential dierence beteen hite noise and pin noise? White noise is e-ual energy per fre-uency and pin noise is e-ual energy per octa!e •
•
•
•
•
•
• •
•
•
•
Unit 4: Introduction to Hearing I
1. )ra a labelled setch detailing the most important physiological features of the human ear.
2. Briey e$plain ho acoustic pressure a!es in the air are con!erted into ner!e impulses in the brain. Mo!ement of perilymph induces localised response in basilar membrane Jrgan of orti responds to bending of hair cells by ring ner!e impulses (ibration of the tympanic membrane is transferred !ia the ossicles to the o!al indo 3. Briey e$plain the function of each of the folloing in the ear# a. +ympanic membrane on!erts acoustic pressure !ariations from the outside orld into mechanical !ibrations in the middle ear b. &inna 4ound locali0ation %together ith the concha' c. ochlea on!erts mechanical !ibrations into ner!e rings to be processed to the brain d. 4emicircular canals /elp you eep your balance by sloshing li-uid around the hairs in the canal e. Jssicles •
•
•
•
•
•
•
+hey act as a mechanical impedance con!erter D. )escribe the perceptual changes that typically occur hen a pure tone $ed in fre-uency is heard ith another pure tone of the same le!el that is sloly !aried in fre-uency from being in unison ith the rst tone to being a perfect fth abo!e it +o tones ith a rough" dissonant -uality are percei!ed o &itches are appro$imately E9199S of a critical bandidth apart 4ingle" una!ering tone is percei!ed o &itches are the same +o completely separate tones are percei!ed" ith no appreciable dissonance o &itches are more than a critical bandidth apart 4ingle tone ith a rough" dissonant -uality is percei!ed o &itches are appro$imately EE9S of a critical bandidth apart. 4ingle" a!ering %beating' tone is percei!ed o &itches are dierent but ithin 1E/0 of one another •
•
•
•
•
•
Unit 5: Introduction to Hearing II
1. )iscuss the range and sensiti!ity of human hearing" including the changes e$pected as e age. A!erage# 29 8 29999/0 By the age of 29" change to# 29 8 1;999/0 ontinues to reduce drastically as e age +his is referred to as presbyacusis 4ensiti!ity# 19E&a to ;D&a %threshold of hearing to threshold of pain' 2. What is the theoretical fre-uency response for human hearing? 29 8 29999/0 3. Briey e$plain the principle of TG-ual 6oudness ontoursR" as stated by ,letcher and Munson" amongst others. An e-ualloudness contour is a measure of sound pressure %dB 4&6'" o!er the fre-uency spectrum" for hich a listener percei!es a constant loudness hen presented ith pure steady tones. +he unit of measurement for loudness le!els is the phon" and is arri!ed at by reference to e-ualloudness contours. D. G$plain the irregular shape of the ,letcherMunson cur!es in terms of the physiology of the ear. /umps and bumps on the cur!e are due to the resonances of the outer ear +he fre-uency response of the ear is not at" thus the strange shape of the graph E. 5n the study of acoustic phenomena" hat are Oeighting cur!esP" and ho might they be abused? Weighting cur!es are used to measure the loudness of sounds by applying a cur!e o!er the soundRs a!e. /oe!er" because of the shape of the cur!es" it often canRt measure the percei!ed loudness of !ery loud bass. • • • • •
•
•
•
•
•
;. What as intended by pro!iding a TloudnessR button on a hi or car audio system" and ho as the implementation of this feature aed? +he loudness button is meant to compensate for the e-ual loudness contours hen listening at lo le!els" but is typically engaged at high !olumes by uninformed consumers" resulting in dangerously loud bass and treble. I. G$plain ho" in 4outh Africa" some employers may be contra!ening the la by subecting their employees to loud music. Aeighting is applied to determine loudness" but prioritises a D/0 range. 5f music falls outside that range" it can be pumped up really high ithout any legal action >. Briey" ho should one interpret the legal limits relating to noise e$posure in the Jccupational /ealth and 4afety Act %1KK3'? >9dB4&6 %or >EdB4&6%A'' o!er > hrs H 3 dB for e!ery hal!ing of time Cse the more accurate eighting cur!e K. Li!e an appro$imate 4&6 gure for each of the folloing en!ironments# a. Uuiet suburban home 3EdB4&6 b. A noisy dance club 129dB4&6 19.What are the most common symptoms of damaged hearing? Audiometric notch at D /0 is symptomatic of noiseinduced hearing loss" as opposed to presbyacusis. Gar pain @inging in the ear &us or uid leaing from the ear (ertigo %especially if a result of diseases such as acoustic neuroma' 11.omplete the folloing# the dierence" in decibels" beteen the softest and loudest sounds a system can produce is called the VVVVVVVVVVVVVVVVVVV of the system. @ange 12.Briey e$plain the primary mechanisms hereby humans distinguish the direction from hich a sound originates. 5nteraural +ime )ierence 8 Which ear hears the sound rst 5nteraural 5ntensity )ierence 8 Which ear hears the sound louder 13.)istinguish beteen delay stereo" intensity stereo" and binaural stereo. )elay stereo o @ecording made ith to microphones placed parallel" a small distance apart 5ntensity stereo o @ecording made ith to microphones placed together but at an angle to each other Binaural stereo o @ecording made ith to microphones placed either side of a dummy head •
•
• • •
•
•
•
• • • •
•
• •
•
•
•
Unit 6: Notes Har!on" I
1. Briey e$plain hy some naturally occurring sounds ha!e a recogni0able pitch" hile others donRt. &itches are sounds consisting mostly of fre-uencies that ha!e a common factor. ot e!ery naturally occurring sound has fre-uencies ith common factors 2. Briey dene the term TtimbreR ith reference to the natural harmonic series. 5f the pattern of !ibration on the basilar membrane !aries hen comparing dierent sounds" for e$ample from a !iolin and a clarinet" then the sounds are percei!ed as ha!ing a dierent OtimbreP 3. Li!e the letter name %pitch' of the se!enth harmonic abo!e the fundamental ). ) D. A perfectly cylindrical pipe" hen blon" sounds the pitch L. 5f a -uarter of this pipe is cut o" hat pitch ill the remaining section of pipe sound hen blon? )? •
•
•
•
Unit #: Notes Har!on" II
1. /oard mentions three mechanisms hich ha!e been considered at some time to account for the O&lace +heoryP of pitch perception" namely loest fre-uency present" smallest linear gap and highest common factor. Briey e$plain ho each of these has been dis-ualied" and hich one best accounts for human pitch perception. 6oest fre-uency present# o 6ocating the fundamental fre-uency o )ismissed by e$perimentation ith spectra lacing a fundamental 4mallest linear gap# o ,inding the smallest fre-uency dierent beteen adacent harmonics o )oes not account for oddharmonic only spectra /ighest common factor# o ,inding the /, of components present o ,ails to account for 4choutenRs T!irtual pitchR o +/54 JG BG4+ AJC+4 ,J@ /CMA &5+/ &G@G&+5J 2. Which aspects of human pitch perception are not accounted for by the O&lace +heoryP of pitch perception? +he ne degree of accuracy of human hearing &erception of sounds hose fre-uency components are not resol!ed by the place mechanism +he pitch percei!ed for some sounds hich ha!e continuous %non harmonic' spectra &itch perception of sounds ith fundamentals less than E9/0 @esolution of harmonics abo!e Ith 3. +he ords TpitchR and Tfre-uencyR are idely held to mean the same thing" though they actually refer to dierent things. G$plain the dierence •
•
•
• •
•
• •
beteen these to terms" gi!ing e$amples of ho TpitchR perception might be inuenced by factors other than ust Tfre-uencyR. &itch is our perception of a sound and fre-uency is the physical ocillations in!ol!ed in producing and maintaining that note. /igher pitches correspond to higher fre-uencies. •
Unit $: Notes Har!on" III
1. /o is the harmonic series typically used to e$plain the e!olution of estern harmony? +he e!olution of Western /armony %in hat harmonies are acceptable' follos the pattern of ascending the harmonic series o Jcta!e o ,ifth o ,ourth o Maor +hird o Minor +hird o Minor +hird %)imished ,ifth?' o Maor second %)ominant 4e!enth? o Maor third o Maor third %Augmented ,ifth?' 2. )escribe the most important features of the graph of percei!ed consonance and dissonance produced by &lomp 7 6e!elt. When the fre-uencies are e-ual %unison' the tones are udged to be Operfectly consonant.P When their fre-uency dierence is greater than one critical bandidth" they are udged consonant. ,or fre-uency dierences of beteen E and E9S of the critical bandidth the inter!al is dissonant. Ma$imum dissonance occurs hen the fre-uency dierence is a -uarter of a critical bandidth. 3. G$plain the acoustic phenomenon of TbeatsR" commonly heard as instruments are being tuned. What is actually happening to cause this beha!iour? A !ibration is basically oscillation beteen to fre-uencies %,1 and ,2'. When ,1 is e-ual to ,2" a single note is heard. As soon as ,2 is mo!ed higher or loer than ,1 a sound ith clearly undulating amplitude !ariations non as ObeatsP is heard •
•
•
•
•
•
Unit %: Notes Har!on" I&
1. What is the &ythagorean comma? +he ratio of tel!e &ythagorean fths to se!en octa!es. 2. What is the syntonic comma? +he ratio of a &ythagorean maor third against a ust maor third. 3. Briey e$plain the term TcentR" as coined by Ale$ander . Gllis. •
•
• •
•
+he e-ual tempered semitone is subdi!ided into Ocents"P here one cent is one hundredth of an e-ual tempered semitone
D. Briey e$plain the fundamental inno!ation underlying meantone temperament. +he meantone scale consists of ust maor thirds %E#D'" e-ualsi0ed hole tones" and fths hich are tuned slightly atter than the pure fth E. Li!e to names associated ith the de!elopment of meantone temperament. Qarlino ,rancis 4alinas ;. Li!e one e$ample of a TolftoneR. G and ,X on the cello I. What ould be the fre-uency of the note that lies a &ythagorean fth belo 1.2 Y/0? >99/0 >. G$press the modern e-ual temperament semitone as a ratio or fraction. •
• •
•
•
•
K. Mention one ad!antage and one disad!antage to the use of e-ual temperament. Ad!antage# All eys are e-ually useable )isad!antage# o inter!al is intune in relation to the inter!als beteen adacent members of the natural harmonic series. +herefore none is perfectly consonant. • •
19.omplete the folloing table for a ust diatonic scale built on #
Name
C
D
E
F
G
A
B
C
Ratio
1/1
9/8
5/4
4/3
3/2
5/3
15/8
2/1
Natural
24
27
30
32
36
40
45
48
Cents
0
204
386
498
702
884
1088
1200
Note
Step
Name
T
t
s
T
t
T
s
Ratio
9/8
10/9
16/15
9/8
10/9
9/8
16/15
Cents
204
182
112
204
182
204
112
11.omplete the folloing table for a &ythagorean diatonic scale built on #
Note
C
D
E
F
G
A
B
C
Ratio
1/1
9/8
81/64
4/3
3/2
27/16
243/128
2/1
—
9/8
9/8
9/8
256/243
—
Step
256/243
9/8
9/8
