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  1. Audio Recording And Production: An Introduction Soam Acharya CS 731 Spring 1998

  2. Contents • sound basics • acoustics/psycho-acoustics • actual recording process

  3. Characterizing Sound • Frequency and Pitch • Amplitude and Loudness • Frequency and Loudness • Acoustic Phase • Timbre

  4. Frequency And Pitch • 20 - 16000 Hz • “feel” outside this range • low bass: 20 - 80 Hz • traffic, thunder, explosions • upper bass: 80 - 320 Hz • fullness/boomy • rhythm instruments: drums, bass, low piano • midrange: 320 - 2560 Hz • fundamental of most sound sources • intensity • upper midrange: 2560 - 5120 Hz • highest sensitivity • treble: 5120 - 20000 Hz • brilliance/sparkle

  5. Amplitude and Loudness • db-SPL = 20 * log10 (sound pressure/ref. sound pressure) • can hear loudness at 1 - 10000000 or greater • the db type measurement also used frequently elsewhere

  6. Airport runway, inside a bass drum Threshold of pain: thunder, “in your face” vocals subway 1” away from acoustic guitar Average conversation Subdued conversation Furnished living room 120 100 80 20 40 140 60 Threshold of hearing 0 Amplitude and Loudness II dB-SPL

  7. Frequency and Loudness [p23 - fig 2-7] (in)equal loudness principle masking equalization

  8. Timbre Tone quality or color

  9. Timbre II Shape of sound or envelope

  10. Acoustics/Psycho-acoustics • direct waves • early reflection • later reflection (reverberation) • body • decay or reverberation time • echo • long reflection path

  11. Sound In An Enclosed Room P35 - 3-2

  12. Reverberation Vs. Decay Time Decay Time Concert hall gymnasium Conference room living room w. rugs Inside a car closet Tiled bathroom Open field Reverberation

  13. Surface Shape of Room Concave: concentrate Concave: disperse Parallel: standing waves

  14. Studio Room Surface P42 - 3-10

  15. Studio Room Materials • Sound absorption coefficient • 0 reflects, 1 absorbs • drapes > glass • porous absorbers • acoustical tiles, carpets, fibreglass, urethane foams • bass taps (diaphragmatic absorbers) • wood panels mounted over air space

  16. Sound to electric signal Analog processing/mixing Computer analog to digital storage digital to analog Processing/editing Actual Recording Process playback

  17. Converting Sound to Electricity: Microphones • moving coil • diaphragm, magnet, coil in a magnetic field • robust, not sensitive to transients, less expensive • ribbon microphone • metal ribbon in a magnetic field • printed ribbon • more robust design • good high frequency response • low output level ie. not sensitive

  18. spacer Back plate Air film Diaphragm - front plate Capacitor/Condenser Microphone • Needs separate power supply for pre-amp • electret type: pre-charged, can get away with batteries • professional use • high sensitivity, output level (large SNR)

  19. Microphone Pickup Patterns • Omnidirectional • all over • non directional • Bidirectional • front and rear • Unidirectional • front only • cardioid • unidirectional

  20. Pickup Patterns II

  21. Pickup Patterns III P 76 - 5-10

  22. Reading A Microphone Spec. Cardioid polar response diagram

  23. Reading a Microphone Spec II Frequency response plot

  24. 1/4” from mic 2” from mic frequency Proximity Effect of Mic. Relative level (dB)

  25. Microphone Accessories I windscreen Pop-screen

  26. Microphone Accessories II XLR -male XLR-female 3.5 “ (miniplug) RCA 1/4”

  27. Specialty Microphones • lavalier • shotgun • parabolic • wireless

  28. Lavalier Microphones • To be worn on lapels • omnidirectional • built-in high freq. boost (chin cutoff)

  29. Wireless Microphones • FM transmitter • UHF/VHF FCC approved • multiple modes

  30. Shotgun Microphones • Long distance pickup • need for unobtrusiveness on sets • attenuate sound from all angles except a narrow one in the front • supercardioid/hypercardioid/ultracardioid • less directional at lower freq.s

  31. Parabolic Microphones • Also long-distance pickup • omni/uni directional microphone

  32. Deploying Microphones • Acoustic/electrical phases • omnidirectional vs. unidirectional • miking speech for radio • miking speech for tv • recording music • reducing unwanted sounds

  33. Acoustic/Electrical Phases • Acoustic phases cancellation • 3:1 rule for microphones • dist between two microphones >= dist between source and main microphone P 292 12-1

  34. Omni vs. Uni directional • Omni • does not have to be held directly in front • picks up more ambience • less susceptible to wind, popping • more resilient to distance • Uni • cuts down unwanted sound • no sense of environment • reduces feedback in reverberant locations

  35. Miking Speech in Radio • Stay within pickup pattern • mic-to-source distance • inverse square law • proximity • weak voice • lip smacking • diffusion of sound quality

  36. Across directional mic face reduces freq. response 45 deg. angle Miking Speech in Radio II P 297 12-5 P297 - 12-6

  37. Stereo Miking • Two microphones • difference in arrival time between microphones • phase problems when combining to mono • Coincident miking • two directional microphones together on same vertical axis • minimize disparity in arrival times

  38. Stereo Miking II P 304, 12-13

  39. Miking for TV • News and interviews • Panel and talk programs • miking the audience

  40. News and Interviews • Omnidirectional lavalier • hide under clothes • rustling/movment • inhibits higher frequencies

  41. Panel and Talk Programs • Host/guest: • Lavalier microphones • unobtrusive • easy to mount • mic-source constant • Mobile host • handheld • pop filter/ shock mount • host can control source distance • go to audience

  42. Miking Audience • Directional shotgun microphones • distribute them in equal quadrants above the audience • audience monitor loudspeaker feedback • offaxis to microphones

  43. Recording Music • Distant miking • ensemble, reduces electronic noise • air loss with distance: freq dependent • phase • close miking • control • better separation of sources

  44. Recording Music II • Miking instruments • drums • bass drum: coil • damping • hi-hat: capacitor • violin/viola • multiple microphones to capture the range • vocals • proximity effect • sibilance • compression

  45. Putting It Together P 409 - 14-67

  46. Reducing Noise • Microphone location • near noisy sources • outdoor location: • noise suppressors (eq dialogue) • shielding • noise gates

  47. Roadmap Sound to electric signal Analog processing/mixing Computer analog to digital storage digital to analog Processing/editing

  48. Analog Processing/Mixing

  49. Analog Processing/Mixing II • Input: • overload indicator • trim • phantom power • equalizer/filter • phase reversal • panning • bus assignment (input signals to output buses) • cuing (for auditioning) • meters • mute

  50. Analog Processing/Mixing III • Output: • buses (to group signals) • bus fader • effects modules • output meter