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Microphone Basics Rick Pitchford, CSRTE Guest Lecture, COM 494 February 2, 2015.

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Presentation on theme: "Microphone Basics Rick Pitchford, CSRTE Guest Lecture, COM 494 February 2, 2015."— Presentation transcript:

1 Microphone Basics Rick Pitchford, CSRTE Guest Lecture, COM 494 February 2, 2015

2 BODY STYLES: hand held lavalier body shotgun headset boom parabolic desk/stand boundary images from RCA, Shure Brothers, Inc., Electrovoice, Audio Technica, Gibson and AKG Microphone Types:

3 A Microphone is a Transducer: A transducer is a device, usually electrical or electronic, that converts one type of energy to another for the purpose of measurement or information transfer. Most transducers are either sensors or actuators. In a broader sense, a transducer is sometimes defined as any device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antennas. In a microphone, the diaphragm moves in response to changing air pressure (sound), creating an electrical current. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers. definitions from wikipedia.org and whatis.com

4 durable; resists humidity and temperature extremes no power supply needed a good quality dynamic is expensive low output level; closer to noise floor hard to physically overdrive the mic element with loud sounds hard to electrically overdrive amp input with loud sounds identical mechanism as loudspeaker Moving Coil (Dynamic) Transducer: image from “First Class Radiotelephone License Handbook”, fourth edition, ©1974, Howard W. Sams Co., Inc.

5 delicate; can be damaged by physical shock, high humidity and temperature extremes requires battery or external “phantom” power supply for the internal amplifier brighter sounding than a dynamic mic more sensitive than dynamic mic of same diaphragm size higher output level than dynamic; can provide better signal-to-noise ratio image from “First Class Radiotelephone License Handbook”, fourth edition, ©1974, Howard W. Sams Co., Inc. Condenser Transducer:

6 Ribbon (Dynamic) Transducer: delicate; easily damaged by shock, humidity and high sound levels desk mount, boom or handheld body styles no power supply needed warm, rich sound very sensitive low output level expensive; difficult to find image from “electronic communication”, third edition, ©1975, McGraw Hill Inc.

7 Microphone Polar Patterns: The sensitivity of a microphone varies depending on the design of the mic, orientation of the sound to the mic and the frequencies considered. This is displayed graphically as a polar pattern. Microphones fit somewhere on a continuum from omni-directional through unidirectional, to bi-directional. In general, mics vary more from their “advertised” patterns as frequency increases. images from “ksm44_en.pdf”, Shure Brothers, Inc. omni uni bi

8 Diaphragm Housing sensitive from all directions has a sealed housing behind the diaphragm positive pressure from any direction pushes the diaphragm in most natural sounding mic pattern due to uniform frequency response Sound Waves Omnidirectional Mics: sensitive

9 more sensitive to the front has a ported housing behind the diaphragm positive pressure from front pushes the diaphragm in positive pressure from rear enters ports, equalizes on both sides of the diaphragm, producing no motion frequency response not uniform off axis usually exhibit “proximity effect” Housing Diaphragm Port Sound Waves Unidirectional Mics: The Cardioid: sensitive null

10 More Unidirectional Mics: supercardioid hypercardioid Housing Diaphragm Port Housing Diaphragm Port As the housing ports become larger, the front sensitivity narrows. A rear sensitivity node forms as nulls move to the sides of the mic, producing the supercardioid and then the hypercardioid. Positive pressure to the rear lobe produces an inverted waveform compared to the front lobe, indicated by the negative sign. + - sensitive null sensitive inverted sensitive null sensitive inverted

11 sensitive front and rear only no housing used around the diaphragm rear entering sounds are naturally inverted relative to the front frequency response not uniform for sounds entering off axis Diaphragm Sound Waves Ribbon Bidirectional Mics: + - null sensitive inverted

12 formed by two identical unidirectional mic capsules mounted back-to-back capsules are connected together electrically out of phase so that positive pressure entering the rear produces inverted waveform compared to positive pressure entering the front, mimicking a ribbon bidirectional Sound Waves Diaphragms Ports Condenser Bidirectional Mics: + - null sensitive inverted

13 omnidirectional mic mounted near a boundary sensitive only on one side of the boundary boundary size determines how closely the mic pattern emulates the “ideal” natural sounding due to uniform frequency response Diaphragm Housing Boundary Hemispherical Mics: sensitive null sensitive

14 Interference Tube Mics: sensitive null sensitive null primarily sensitive to the front a slotted tube is fitted to the front of a non-ported housing sound pressure waves from the front travel down the tube to the diaphragm sound pressure waves from the side enter the tube through slots and travel down the tube by varying-length paths off axis sounds cancel at the end of the tube – a process called comb filtering polar pattern varies with frequency Housing Diaphragm Slotted Tube

15 the effect of mixing two identical signals, one delayed in time from the other all frequencies in the delayed signal are delayed by the same amount of time different phase delays are created for different frequencies because every frequency has a unique wavelength the sum of the two signals exhibits a frequency response of alternating peaks and nulls frequency level Comb Filtering:

16 the same time delay has the exact opposite affect on these two frequencies at 1 msec. all even multiples of 500 Hz., (1000 Hz., 2000 Hz., 3000 Hz., etc.) will fully reinforce; all odd multiples (500 Hz., 1500 Hz., 2500 Hz., etc.) will fully cancel at frequencies in between, the interaction will vary from reinforcement to cancellation 1msec = 1 foot additional acoustic path length level time level time level 1 msec Hz. level time 1 msec. time level 500 Hz. For Example, +=+= +=+=

17 Non-Acoustic Comb Filtering: First 5-6 weeks of ABC’s Spring, 2009 season live broadcast of Dancing With the Stars demonstrated severe comb filtering. Commercial breaks were not affected. The problem may have been caused by mis-timed, redundant signal paths being summed. Frequency response of commercial break Frequency response of live program

18 Taming Acoustic Comb Filtering: frequency level place the mic in such a position that reflections are delayed only slightly; smaller delays push the first null point to higher frequencies place the mic closer to the sound source and further from the reflectors so the Inverse Square law helps the direct sound overwhelm the reflected sounds

19 Mic Placement: Obey the Inverse Square Law! Doubling the distance from source to transducer quarters the sound pressure level on the diaphragm. Halving the distance from source to transducer quadruples the sound pressure level on the diaphragm.

20 Proximity Effect: image from “us_pro_beta57a_ug.pdf”, Shure Brothers Inc., 2004 ~17dB change at 100Hz, from 1/8 inch to 24 inches DIRECTIONAL MICS respond to the Inverse Square law differently than omnidirectional microphones. Low frequencies are enhanced more than mid and high frequencies as the source-to-mic spacing decreases. This is the reason many performers and announcers work directional microphones closely, giving their voice more low end. Be aware varying source-to-mic spacing during a performance can drastically change the timbre of the voice. Many directional mics include a bass-rolloff switch to equalize this effect for close-micing situations. Some mics are carefully designed to minimize it.

21 Selecting a Mic: Using a mic for a particular situation requires these decisions be made about: the appropriate body style the appropriate transducer type the best polar pattern to use the proximity of the mic to the source handling sound reflections

22 Body Style Selection: Hand held: “universal” Lavalier : spoken voice some instruments Body: stage or screen Shotgun : high-noise situations Headset : hands-free uses sports commentators performers Boom : instrument studio voice Parabolic : sports sidelines surveillance Desk : interview Boundary : complete room coverage conferences

23 Transducer Selection: Moving Coil: extremely loud sounds sports remotes emergency/backup mic general purpose bad weather situations Condenser: extremely quiet sounds high quality recording on a budget covert/concealed applications near strong magnetic fields Ribbon: predictable sound levels controlled studio locations experienced performers feeding high-gain, low- noise amplifiers

24 Polar Pattern Selection: Consider both the desired and all UNDESIRED sound sources when choosing a pattern. Use the best pattern to attenuate undesired audio as well as delayed reflections of desired audio.

25 Multiple Mics for Mono work: large sound source needing coverage multiple sound sources Beware comb filter effects! Micing in Stereo requires a minimum of two discreet signals, Left and Right. Stereo is a spatial effect stemming from both intensity and time differences of sounds stimulating left and right ears or the ear’s representatives, the microphones. Consideration must be given to mono mixes derived from stereo signals. Multiple Mics for Mono and Stereo:

26 two mics placed in front of and facing sound source (center mic, fed to both channels, is optional) spacial (stereo) effect due to both time and intensity differences mic placement must follow "3 to 1" rule to minimize comb filtering effect in mono recreates a sound field in one dimension; listener movements will change the mix Sound Source 8 ft. 25 ft. Spaced Pair (A-B Pair): L (C) R

27 crossed or head-to- head unidirectional mics placed in front of and centered on a sound source spacial (stereo) effect due to intensity differences only no comb filtering effects in mono - fully mono compatible recreates an aural sweet-spot Sound Source Coincident Pair (X-Y Pair): R L

28 + - ORTF cardioid microphones at an angle of 110° spaced about 6.5 inches apart susceptible to comb filtering recreates a head-sized sound field 6-7” Coincident Pair Deviations: Blumlein Pair developed in 1931 crossed bi-directional mics placed head-to-head not susceptible to comb filtering recreates a sweet spot Sound Source L R

29 Sound Source mid mic picks up left plus right (mono/sum) signal side mic picks up left minus right (difference) signal adding side to mid gives double left signal (L+R) + (L-R) = 2L subtracting side from mid gives double right signal (L+R) - (L-R) = (L+R) + (-L+R) = 2R spacial (stereo) effect due to intensity differences only no comb filtering effects in mono - fully mono compatible recreates sweet spot MID mic is UNIDIRECTIONAL facing forward SIDE mic is BIDIRECTIONAL facing left/right L+R L -R Mid/Side (M-S): + -

30 combine multiple AB, XY, MS, ORTF and/or Blumlein mic pairs with or without accent mics spacial (stereo) effect due (hopefully) to intensity differences only mic placement must still follow "3 to 1" rule to minimize comb filtering effect in summed L and R channels aspects of both a sound field and multiple sweet spots DRUMS HORNS Multi-Mic: PIANO + - STRINGS

31 one mic (or direct connection) per source, each recorded separately high acoustic isolation required between mics to prevent leakage no natural spacial (stereo) effect - artificially created during the track mixdown multi-track mono - not true stereo produces a totally synthetic sound field DRUMS HORNS GUITARS VOCAL 1 VOCAL 2 KEYBOARDS Close Mic:

32 Beyond Stereo: consumer multi-track “surround sound” systems are everywhere quadraphonic sound of the 1970s fell flat due to competing incompatible formats, poor results, questionable production practices and music-only implementation Dolby Surround presentation of major films and the emergence of HiFi home video formats in the 1980s re-awakened consumer interest “5.1” surround systems consist of left, center, right, left and right surround, and LFE (non-directional, low frequency/effects) channels surround sound tracks are usually “built” from dry, close-mic, multitrack original material recorded in studio/sound stage “live” surround recording techniques are emerging based on established stereo practices

33 Spaced Surround: Sound Field mics are suspended above audience space in trapezoid arrangement front spaced omnis for left and right rear spaced omnis for left/right surround single unidirectional for center channel and LFE placed somewhere in front of or within trapezoid spacial effect due to both time and intensity differences recreates the sound field in two dimensions; listener can move around to change aural perspective L, R, Ls, Rs C

34 Coincident Surround: mics are either suspended above or located in audience space left, center, right, left and right surround unidirectionals are mounted crossed or within a “dummy head” down-facing omni for LFE pickup spacial effect due to intensity differences only re-creates specific aural sweet-spot to locate listener; movement within the sound field doesn’t change perspective greatly stereo and mono compatible; no comb filtering L, C, R, Ls, Rs LFE Sound Field

35 MSM Surround Array: L F +R F L -R MID mics are UNIDIRECTIONAL facing forward and rearward SIDE mic is BIDIRECTIONAL facing left/right + - L R +R R Sound Field three mics pick up front, rear and side audio adding and subtracting side signal from front and rear produce Left front, Right front, Left rear and Right rear LFE and Center channels derived or from additional dedicated mics recreates a sweet-spot stereo and mono compatible; no comb filtering

36 “Sports Event Capture Array-2” designed for 2-goal sporting events first used for 2003 NCAA TV broadcasts on CBS mic arrays mount on backboard, goal stands, etc., provide front and rear L/R audio two supercardioid mics spaced 11” apart, face forward, down and slightly in mid-side pair centered between and facing back toward seating area center channel is feed from the announcers; LFE is derived from the array via low-pass filters L, R Ls, Rs + -

37 ESPN Monday Night Football: coincident (XY) pair of shotguns on 50 yd line to pick up crowd on opposite side for L, R coincident (XY) pair at top of stadium for Ls, Rs stereo wireless on umpire for field ambience; L, R 6 wireless parabolic mics for field effects; L, R umpire and player wireless, synthesized to stereo, for field perspective; L, R music to L, R all cameras have mounted mics for shot perspective announcers mics to Center only L, R, Ls, Rs image from

38 Fox Football: coincident (XY) pairs on opposite 25 yd. lines to pick up crowd; L, R spaced (AB) pair hung from press box for crowd surround; Ls, Rs umpire and player wireless, synthesized to stereo, for field perspective; L, R 4 wireless parabolics plus camera mounted mics on field for shot perspective; L, R as needed music to L, R; sound effects produced in 5.1 announcers mics to Center only L, R, Ls, Rs image from

39 World Series on Fox: image from parabolic mics high behind home plate, down first and third base lines, focused on home plate, to L & R AB pair at high first and high third pointed across field to farthest crowd to L, R omnis mounted in bases, pointed toward outfield, to L, L & R, R three or four manned parabolic mics in the outfield, to L, R XY configured shotguns in centerfield, to Ls, Rs “a bunch” of hemispherical mics and lavs on “anything that makes noise” music to L, R; sound effects produced in 5.1 announcers mics to Center only

40 five short shotguns on the table aimed at each basket, center court, and to either side of the center 12 boundary mics on the court one boundary mic below each basket music to L, R; sound effects produced in 5.1 announcers mics to Center only NBA: image from

41 Other Sporting Events: Golf: a stereo mic on a stake at the tee two stereo shotguns on the greens stereo mics for the crowd in the long shotguns with operators on the fairway “bird mics” in the trees Mixed Martial Arts: a cluster of five shotguns: one picking up the center of the ring, the other four splayed to capture the rest of the circular cage shotguns on boom poles lavs placed under the pad around the ring mics on the 9 handheld cameras

42 “The Two Towers” high strings woodwinds low strings woodwinds percussion brass captured near-100 piece orchestra in a 135’ X 75’ auditorium three omnidirectional mics on a Decca Tree over conductor’s head; L, C, R two omnidirectional mics wide and outside of strings; L, R two omnidirectional mics very high and rear facing for Ls, Rs various omnidirectional mics for spot pickup 4.5’ Decca 6’ Tree all mics

43 end


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