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Metropolitan Community College
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  1. MetropolitanCommunityCollege Audio Video Production Engineering Part 1 Audio Rev. 6.4d

  2. Nature of Sound Waves • Sounds in air are commonly produced Vocal cords, Speakers, Instruments, etc. 2

  3. Air particles • As the sound source pushes against air particles they are compressed. • As the sound source moves away they are rarefied. 3

  4. 4

  5. Loudness VS Distance • Loudness follows an Inverse-Square Law • Intensity of sound is inversely proportional to the square of the distance from the source. 5

  6. Sound and Hearing • The Human Ear • Outer Ear • Middle Ear • Inner Ear 6

  7. Labyrinth Pinna Courtesy of Dr. John S. Oghalai Used by permission 7

  8. Courtesy of Dr. John S. Oghalai Used by permission 8

  9. Frequency and Sound 960 Hz • 20 Hz 60 Hz 1920 Hz 120 Hz 3840Hz 240 Hz 7680 Hz 480 Hz 15360 Hz 9

  10. 10

  11. Wavelength & Frequency 11

  12. Amplitude & Phase 12

  13. 13

  14. Decibel • Unit of measure Bel • Based on ratio • Used for both Acoustic and electrical applications 14

  15. dB formulas • Power • dB = 10 log (P1/P0) • Voltage and Acoustic • dB = 20 log (E1/E0) 15

  16. dB as Unit of Measure • Requires a reference • 3 and 10 rule (power) • 6 and 20 rule 16

  17. 3 & 10 and 6 & 20 Rule 17

  18. Add and Subtract dB 18

  19. dB Standards • 0 dBW = 1W • 100W amplifier is 20dBW • 1000W amplifier is 30dBW 19

  20. dB Standards • 0 dBm = 1mw>600 Ohm load (.775 V) • 0 dBu = .775 V • 0 dBv = .775 V • 0 dBV = 1 V 20

  21. Click chart for sound 21

  22. SPL Meter • Microphone Amplifier Meter • A Weighting filter inverse of equal loudness contours • B & C Weighting high end of equal loudness contours 22

  23. Weighting Networks • A weighting 10 – 55 dB • B weighting 55 – 85 dB • C weighting 85 – 140 dB 23

  24. Weighting Chart 24

  25. Loudness of sound (dB) • Threshold of hearing 0 • Normal conversation 60 • City traffic inside car 85 • Sustained exposure results in hearing loss 85-90 • Power Mower 107 25

  26. Loudness of sound (dB) • Rock concert front row 115 • Pain begins 120 • Jet engine @ 100’ 140 • Death of hearing tissue 180 • Loudest sound possible 194 26

  27. dB Meter • Specialized AC Meter with scale calibrated in dB 27

  28. VU Meter • Much the same as dB meter • Calibrated 0VU = __dB • Response peak to average • Analog, LED, Electronic display 28

  29. Noise InducedHearing Loss • Base level 85 dB for 8 hrs • Each 3 db increase 1/2 time • “A” weighting measurement • Most sensitive at 4 KHz • 40 yrs @ 85dB = NIHL 8% 29

  30. 30

  31. End Week 1 • Review Week 2 31

  32. 32

  33. Magnetic Polarity • Like Poles Repel • Unlike Poles Attract 33

  34. 34

  35. Electromagnetic Interference • A Moving magnetic field across a stationary conductor has same effect as a moving conductor in a stationary magnetic field 35

  36. Magnetic field is generated around wires carrying current • Magnetic polarity changes as direction of current flow changes 36

  37. Capacitors • Two metallic plates • Insulated from each other • (insulation called dielectric) 37

  38. 38

  39. Capacitors store electrons • Capacitors behave much like a water tower • Filling the water tower is like charging a capacitor • Using the water is like discharging a capacitor 39

  40. Unit of Measure • The Farad is the unit of measure. Typical values are Micro Farad or Pico Farad. Larger values store more electrons. 40

  41. Capacitor Behavior • Capacitors block DC current and pass AC current 41

  42. Capacitor Behavior 42

  43. Dynamic Capacitor • Microphone Microphone RibbonMicrophone 43

  44. Microphone Pickup Patterns • Omni-directional: picks up sound from all directions • Directional: picks up sound from one direction • Bi-directional: picks up sound from two directions 44

  45. Pick-up Patterns 45

  46. Polar Pattern 46

  47. Directional Microphones • Directional Microphones called Cardioid, Supercardioid, Hypercardioid 47

  48. Directional Microphones • Proximity effect • Do not “reach” further • Generally do not have as smooth of a response curve as Omni-directional 48

  49. Phantom Power 2 3 1 49

  50. Muting Capacitor Mics 50