Nature of Sound• Sound is a longitudinal wave motionconsisting of a train of Compression andrarefaction travelling in a medium. Whenthese waves strike the eardrum these areconverted into signals which are carried tothe brain by the auditory nerves and arefinally interpreted into what we call Sound.
SOUND WAVESOUND WAVEMOLECULESMOLECULES1.2. SoundwavesSourceofSoundRegion of High Pressure (Compression) andRegion of low pressure (Rarefaction)
Pressure and intensity ofSound waves• Sound waves produce variation of pressurein the medium in the form of compressionsand rarefactions in quick successions.Sound pressure variation is thereforerepresented by newton per square metre(N/m2), or pascal (Pa). In terms of micro-bar (dyne per Sq cm) one Pa is equal to tenmicro-bars.
Sound & Sensitivity ofhuman-ear:• Human ear is very sensitive to soundintensity & can detect sound aslow as 0.1 pW/m2(or 10 dB below thethreshold of hearing).• The ear cannot distinguish difference ofintensity of less than 1 dB between twosounds.
• Minimum level which can be comfortablydetected over threshold of hearing is 3 dbfor speech or music.• The ear possesses characteristics ofmasking that is the louder sound reachingthe ear can suppress the weaker sound.• The ear judges’ direction of sound from thefirst received even if it is weaker.
COMPONENTS OF SOUND IN AN ENCLOSEDSPACE- Direct Sound- Reflected Sound
Loudness & Phon• Loudness is defined as the intensity ofsound as judged by the ear. It needs higherintensity at low frequencies than at highfrequencies to impart same sensation ofloudness.• The intensity of 60 dB at 40 Hz and of 0 dBat 1000 Hz imparts the same loudness.
Phon :The intensity in dB with reference toThreshold of hearing as perceived by theear at 1000 Hz is called phon (P). If it is 0dB then loudness is 0 phon, if it is 40 dBthen loudness is 40 phon.
Sone: It is found that a 10 dB increase insound level corresponds approximately to aperceived doubling of loudness. One sone isdefined as the loudness expressed by aperson listening to a 1000 Hz tone of 40phon loudness level. Similarly 50 phonswould have a loudness of 2 sones, 60 phonswould be 4 sones, etc. The relationbetween sone (L) and Phon (P) is given by-10logL= (P - 40) log2
FrequencyFletcher-Munson Curves for loudness vs. Frequency
Frequency range for SpeechAudible frequencies range from 16Hz to20000 Hz. For satisfactory transmission ofspeech two factors are very important.• Intelligibility- It is defined as theclearness of one’s speech determinedthrough the test of articulation.• Energy-The energy in speech is containedmostly in the low frequencies.
Overtones and Timbre• Sound waves produced by Speech andmusical instruments are not pure sinewaves, but are complex waves consistingnot only the fundamental frequencies(tones) but also of their harmonics, andother frequencies, called ‘overtones’. Theproportion of tones & overtones present inthe sound that helps us to identify anyparticular voice is called Timbre.
• Intervals: It is defined as the ratio of twofrequencies.Example-Interval of 400Hz &100Hz is 4.• Octaves: An interval of 1:2is called anOCTAVE.Example: One octave of 200 Hz is400 Hz• Harmonics: It is an integer ratio betweentwo frequencies.Example: 2ndharmonicof 100Hz is 200Hz
PitchIt generally represents the perceivedfundamental frequency of a sound. Soundwaves with a longer wavelength dontarrive at the ear, as often (frequently) as theshorter waves. The shorter the wavelength,the higher the frequency, and the higher thepitch, of the sound. In other words, shortwaves sound high; long waves sound low.
Acoustic Reverberation• The term acoustics has been derived fromthe Greek word akoustos, meaning“hearing.” It is the area of science devotedto the study of the production, transmission,reception, and effect of sound.• In the field of broadcasting the broadcaststudios are the originating place of theprogram to be broadcast live, or recordedfor future use. Hence proper care should betaken in their designing and construction.
Reverberation• The persistence of sound, caused due torepeated reflection is called reverberation.• In an studio the sound is received directlyfrom the source as well as sound reflectedfrom walls, floor, ceiling, etc. The soundpersists for a noticeable time even after theoriginal sound stops. It fades awaygradually.
MicrophoneMicrophone is a transducer.It converts sound wave(acoustical energy) into electrical energyFive important characteristics of microphone• Operating principle• Frequency response• Directionality of microphone• Electrical output and• Physical design of the microphone
Pressure-operated Microphones• Sound pressure is applied onone side of the diaphragm.• Electrical output isproportional to the soundpressure.• Theoretically omnidirectional.• However,the physical size ofmicrophone works as anobstacle at high frequency.• Sensitivity at HF decreases.Operating Principle
Pressure Gradient(velocity)Operated Microphones• Both sides of thediaphragm areexposed to the soundpressure.• Hence, the electricaloutput is proportionalto the difference inpressure on the twosides.Operating Principle
Combined-operationMicrophones• The principle of pressure-operated microphones andpressure gradient operatedmicrophones are combinedto get maximum sensitivityin one direction andminimum sensitivity in theopposite direction.• Unidirectionalcharacteristics. An Acoustic Labyrinth
Electrodynamic Microphone withMoving Coil• A dense coil of wiremoves within a strongelectromagnetic field.• Induced current isproportional todisplacement velocity.• Great mechanicalrobustness..Operating Principle
Electrodynamic Microphone withMoving Coil - cont’d• The dense coil of wire makes itless sensitive especially to verysoft sounds or high pitch sounds(sibilants or harmonics).• Used in live performance whererough handling is common.• Examples- AKG D-202, D-222,D-900, D-770, D-190E, SM58,SM57, SM48 etc.AKG D-770Instrument/VocalMicrophone
Electrodynamic RibbonMicrophone• The coil of moving coilmicrophone is replaced bya corrugated thin strip ofaluminium.• Very sensitive to shockand large sound volumes.• Very delicate.• Unusable in windycondition.Operating Principle
Electrostatic(Condenser)Microphones(single diaphragm)• A thick metallic plate as adiaphragm is fixed to aperforated metal back plate.• Electrical charge is appliedto either or both plates.• Sounds pressure changesthe distance between twoplates and causes variationin the capacitance.• Requires in-built pre-amp Operating Principle
Electrostatic(Condenser)Microphones(single diaphragm)-cont’d• High sensitivity and very good frequency response.• Smaller and lighter diaphragm gives more accurateand pin-sharp sound.• Requires external power supply popularly known as“Phantom Power Supply” - 9v to 52v.• Very sensitive to humidity and temperature.• Less sensitive to shock.• High cost.
Electrostatic(Condenser)Microphones(single diaphragm)-cont’d• Tends to record sound as itreally is.• Large diaphragm gives flatteringresponse.• Resonant frequency at the upperend of audio spectrum.• Examples- C2000B, C3000B,SM86, SM94, SM81 etc.SHURESM94Instrument Mic.
Electret Microphone• It is a modified form ofcondenser microphone.• It does not use externalpower supply.• Either diaphragm or back-plate is permanentlycharged.• However, pre-amp requirespower supply.Electret
Electret Microphone- cont’d• The output is independent of the diaphragmsurface area.• Light and small in size.• Excellent quality/price ratio.• However, not suitable for bass.
Omnidirectional Microphones• Gain remains constant inall directions-It is unity.• However, true Omni ispossible at low frequencyonly.• Moving coil and Condensermicrophones are designedto work as omnidirectionalmicrophones.Omnidirectional
Omnidirectional Microphones-cont’d• Pickup angle-360 degree.• No proximity effect.• Used for recording ambientand background sound andalso for vocals.• Examples- C4000B,C414B, C577WR, D230• C4000B has dual largediaphragm.
Bi-directional Microphones• Figure of 8 pattern.• Gain is proportional to cosineof angle of incident of sound.• Pickup angle-90 degree(120degree at -6dB)• Limited use.• Example- Ribbon Microphone,Condenser Microphone
Cardioid Microphones• Gain= 1+cosine of angle ofincident of sound.• Heart -shaped.• Pickup angle(Coverage angle) -130 degree.(180 degree at-6dB)• Null angle - 180 degree.• Degenerates towards omni(Hypocardioid) at low frequency.Cardioid
Cardioid Microphones- cont’d• More directional thanrequired at high frequency.• Favoured for stage use as itprevents feedback.• Examples- AKG D770,C3000B, C2000B etc.
Hypercardioid Microphones• Gain= 0.5+cosine of angle of incidentof sound.• Cardioid +Bidirectional• Pickup angle - 105 degree.(140degree at -6dB)• Null angle - 110 degree.• Narrower pick-up than cardioid,hence feedback rejection improveseven further.• The least overall pickup of ambientsound.• Examples- C1000S, D660Shypercardioid
Supercardioid Microphones• Pickup angle - 115 degree.• Null angle - 125 degree.• Maximum ratio of on-axispickup to ambient pickup.• Useful for more distantpickup or in higher ambientnoise level.• Examples- D880/D880S,Beta58A, Beta87A etc.
Unidirectional Microphones• The term is used for ‘Gun’microphone.• Long and rod shaped.• Good for recording singlevoice in noisy locations.• Also used for picking upvoice from long distance.• Shotgun(18 in. long), Longgun(36 in. long).• Long gun pick-up-20 to 25feet.• Example- D900.sGUN MICROPHONE
Electrodynamic Microphone for recording ofvoice in hand held conditionUses • Recording of interview of players and sportsauthority.• Less sensitive so suitable for noisy situation• Mechanically strong and robust Examples- AKG D-202,D-222, D-900, D-770, D-190E, SM58, SM57, SM48SHURESM58VocalMicrophoneAKGD190ESpeech/InstrumentMicrophone
Condenser MicrophoneUses• Tends to record sound asit really is.• Broad Frequencyspectrum.• Uses to record whensound source is not near• Examples- C2000B,C3000B, SM86, SM94,SM81 etcSHURESM81
Lip Microphone• A close talking microphone.• Designed to ensure constantspacing between themicrophone body and the lipsof the user.• Also known as noise cancelingmicrophone• Similar to ribbon microphone.• Used for radio reporting andsports commentary.Lip Microphone
Gun Microphones• Highly unidirectional• Long and rod shaped.• Good for recording singlevoice in noisy locations.• Good for recording soundeffect from a far distance.• Also used for picking upvoice from long distance.• Shotgun(18 in. long), Longgun(36 in. long).• Long gun pick-up-20 to 25feet.• Example- D900.GUN MICROPHONE
Lapel Microphones• It is usually electretmicrophone.• Based on Lavalier Technology.• Omni directional polar pattern.• Very small and light- weight.• Offers reasonable intelligibilityin fairly noisy surrounding.• High frequency loss whenhidden behind clothing.Lapel Microphone
Lapel Microphones-cont’d• Also called as neck microphone.• May be corded or cordless.• Worn at the chest or clipped to clothing.• It can be powered by batteries or phantom power.• Suitable for running commentary or a lecture.• Can also be used for wind instrument.
Parabolic Microphone• A cardioid microphone isplaced at the focal point of aparabolic reflector.• The parabolic reflector is madeof sheet metal or stratifiedpolyester or glass fibre.• Low frequency pickup isproportional to the diameter ofthe reflector.• Used for recording faint soundssuch as birdsong.Operating principle
Boundary Microphone• A small capsule microphoneusually an electret, is housedin a flat receptacle.• The flat receptacle works asa plane reflective surface.• The directivity ishemispherical at allfrequencies.• More dynamic range andclarity.Omnidirectional.• Also known as PZM.Pressure Zone Microphone
Contact Microphone• Size is small.• Attached with thesound source itself.• Pickup vibrationpulsing throughsolid.• Attach to a point sothat it should notcome in the view ofcamera.• HF response isgood but LFresponse is bad.
Wireless Microphones• These are ordinarymicrophones with an FMtransmitter.• Provides complete freedomof movement.• Lapel type or handheld.• Omnidirectional.• Interference from outsidesource.• Suitable for stageperformance.• Suitable for places wherelaying of microphone cableis not possibleSHURE MICROPHONELapel MicTransmitterReceiverHandheldMic.
Placement of Microphones• Placement of microphones depends on the acousticnature of the sound source and the acousticcharacteristics of the microphones.• Always use minimum number of microphones.• Microphone should be placed with its 0 axis facingthe source of sound to avoid off axis colouration.• When two or more microphones are used, it shouldbe ensured that their outputs are in phase.• The Microphone should not be too close or too farto the sound source.
Placement of Microphones-cont’d• When the Microphone is close to the sound source,direct sound is predominant and hence the outputappears to be ‘dry’. When it is far away from thesound source, the reverberant (indirect) sound ispredominant and hence the output lacks in clarity.• Microphone should not be placed very close to areflecting surface like bare walls, hard tables etc.• Directional microphones should not be placed tooclose to the source of sound to avoid boosting oflow frequencies due to a phenomenon calledproximity effect.
Placement of Microphones-cont’dThis effect should be normally avoided by placingthe microphones fairly away (30-45 cm) from thesource of sound.• For spoken word recordings, microphones shouldnot be placed directly in line with the mouth since itwill result in ‘p’ blasting.• A talker should not hold the script between his faceand the microphone otherwise shadowing effect willoccur at high frequencies.
Placement of Microphones-cont’d• For stringed instruments (violin,sitar,sarangi,etc.) 0axis of the microphone should be preferably placednormal to the front face of the instrument.• For instrument with large sound output (like drumsand other percussion and bass instrument) themicrophone should be placed well away from thesource of sound.• For wood wind instrument where the instrument isnot particularly direction (such as flute) themicrophone may be placed about 60 cm.away .
Placement of Microphones-cont’d• In outdoor locations because of the higher ambientnoise level, the working distance must be kept lessthan the corresponding distance when workingindoors.• When using multiple microphones, to reduceacoustic interference between the microphonesTHREE-to-ONE rule should be followed, whichstates that the microphone-to- microphone distanceshould be at least three times the source-to-microphone distance.
Placement of Microphones• Microphoneshould be placedwith its 0 axisfacing the sourceof sound to avoidoff axis effect.• The Microphoneshould not be tooclose or too far tothe sound source.