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Metropolitan Community College

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    1. Metropolitan Community College Audio Video Production Engineering Part 1 Audio

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

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

    4. 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. Sound level of 65 dB at 3 At 6 the level is 59 dB (-6) At 12 the level is 53dB (another -6)

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

    10. Frequency and Sound 20 Hz

    12. Wavelength & Frequency

    13. Amplitude & Phase

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

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

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

    18. 3 & 10 and 6 & 20 Rule

    19. Add and Subtract dB

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

    21. dB Standards dB-SPL Acoustic sound Pressure Reference 0.0002 Dynes/sq cm

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

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

    25. Weighting Networks A weighting 10 55 dB B weighting 55 85 dB C weighting 85 140 dB

    26. Weighting Chart

    27. Loudness of sound (dB) Threshold of hearing 0 Normal conversation 65 City traffic inside car 85 Train Whistle 500 90 Sustained exposure results in hearing loss 85-90

    28. Loudness of sound (dB) Power Mower 107 Pain begins 125 Jet engine @ 100 140 Death of hearing tissue 180 Loudest sound possible 194

    29. dB Meter Specialized AC Meter with scale calibrated in dB

    30. VU Meter Much the same as dB meter Calibrated 0VU = _dB Response peak to average Analog, LED, Electronic display End of 2nd weekEnd of 2nd week

    31. Noise Induced Hearing 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%

    33. Review Week 1

    35. Magnetic Polarity Like Poles Repel Unlike Poles Attract

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

    38. Magnetic field is generated around wires carrying current Magnetic polarity changes as direction of current flow changes End of first weekEnd of first week

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

    40. 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

    41. Unit of Measure The Farad is the unit of measure. Typical values are Micro Farad or Pico Farad

    42. Capacitor Behavior Capacitors block DC current and pass AC current

    43. Dynamic Capacitor Microphone Microphone

    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

    45. Polar Pattern

    46. Directional Microphones Directional Microphones called Cardioid, Supercardioid, Hypercardioid

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

    48. The 3 to 1 rule The distance between microphones should be at least 3 times the distance from each microphone to its intended sound source.

    49. How Speakers Work

    50. Block Diagrams Used to make complex circuits or systems easy for the user to comprehend and use

    51. Block Diagrams Most common symbol is a square or rectangle Triangles often used Interconnected by lines

    52. Block Diagrams Direction of lines important INPUTS top and left OUTPUTS - bottom and right Use arrows when not standard

    55. Amplifiers Electronic devices used to increase an electronic signal level Many types and kinds

    56. Amplifier Characteristics Gain Impedance input/output Balanced input/output Unbalanced input/output

    57. Audio Amplifier Types Pre amplifier Buffer amplifier Line amplifier/DA Power amplifier

    58. Pre Amplifier Frequently used in low level applications Phonograph cartridge Microphone Intercom

    59. Buffer Often used to isolate one circuit from another and to match impedances

    60. Line Amplifier/DA Often used to increase drive capability Split signals to feed several different pieces of equipt. Usually no change in level

    61. Power Amplifiers Usually used to increase current capability to drive speakers and headphones

    62. Review Week 2

    63. Ohms Law E=IR E is voltage in volts I is current in amps R is resistance in Ohms

    64. Rearranging Formula E=IR I=E/R R=E/I

    65. Power Law (Watts Law) P=IE P is power in watts I is current in amps E is voltage in volts

    66. Rearranging Formula P=IE P=I2R P=E2/R I=P/E E=P/I

    67. Impedance The total opposition to an alternating current and is measured in Ohms Symbol for impedance is Z

    68. Complex calculations Impedance = square root of reactance squared + resistance squared.

    69. Reactance & Frequency Capacitive Reactance Xc=1/2?fC Inductive Reactance Xl=2?fL

    70. Wiring Characteristics Impedance and Resistance Impedance for AC circuits Resistance for DC circuits Both measured in Ohms

    71. Measurement Resistance measured directly with meter Impedance calculated or measured with bridge

    72. Bridge Measurement

    73. Cable Characteristics Conductor size (AWG) Number of Conductors Twist or no twist Shielding Insulation type End of 3rd weekEnd of 3rd week

    74. AWG 24-26 Guage used for Phone & Computer wiring 22 Guage often used for Audio Mic. & Line level 16-18 Guage 70V Speaker distribution

    75. AWG 18-10 Guage used for 2 O -16 O speakers

    76. Number of Conductors Unbalanced audio 1 conductor plus shield or ground connection. 2 conductors needed to complete circuit

    77. Number of Conductors Balanced audio 2 conductors, may also have a shield but not required Speaker 2 conductors with no shield

    78. Twist or No Twist Twisted pairs used with low level audio and many other services (data, phone, etc.) No twist mainly for power

    79. Shielding Shield must be connected on both ends for Phantom powering of microphones Connecting shields on one end may be good for hum, but increases RFI chances

    80. Insulation Type Plenum and non-plenum Portable and Installed wire RoHS compliant

    81. RoHS Compliant The RoHS directive aims to restrict certain dangerous substances commonly used in electronic and electronic equipment (Restriction of Use of Hazardous Substances)

    82. RoHS Compliant . Any RoHS compliant component is tested for the presence of Lead (Pb), Cadmium (Cd), Mercury (Hg), Hexavalent chromium (Hex-Cr),

    83. RoHS Compliant Polybrominated biphenyls (PBB), and Polybrominated diphenyl ethers (PBDE). Some military and medical equipment are exempt from RoHS compliance.

    84. Speaker Wiring

    85. Wire Calculator

    86. Balanced Wiring

    87. Common Mode Rejection

    88. Unbalanced Wiring

    89. Audio Class of Service Microphone level (-50 dB) Line level (0 dB) Speaker level Video (1V Noisy) RF (Saturates Amplifiers) Data (HF Noisy)

    90. Review Week 3

    91. Equipment Interconnect Power Grounding Earth/Chassis Signal Grounding Go to EPM Mixer guide PP12

    92. Transformers Turns Ratio Step-up/Step-down Impedance Other Properties See also

    93. Power For Equipment

    94. Two Bus for 220V

    95. Transformer Isolation

    96. Patch Panels

    97. The right way to do it.

    99. See Also EPM Mixer guide pg 30 Off the Shelf cable (B) 6dB sig. loss

    101. End of week 4End of week 4

    102. Soldering Connectors See A guide to soldering and EPE basic soldering guide on my Website

    103. Soldering Video RCA connectors connectors XLR connectors

    104. Equalization Very complex topic Sound reinforcement Vocal Instruments

    105. Sound Reinforcement There is no one correct way to equalize a sound system. Type of system and size of the space has a giant impact EQ technique.

    106. Distributed Sound Using Parametric EQ, try to adjust the system EQ using pink noise and spectrum analyzer for near flat response (slight HF roll off OK)

    107. System EQ Once System EQ is adjusted, individual vocal channels or instrument channels may be adjusted for BEST MIX

    108. Basic Terms Octave An octave is the interval between two points where the frequency at the second point is twice the frequency of the first.

    109. Frequency & Octaves 63 Hz 1 125 Hz 2 250 Hz 3 500 Hz 4 1 KHz 5 2 KHz 6 4 KHz 7 8 KHz 8 16 KHz 9

    110. Q rating The "Q" control sets the width of the band of frequencies that will be boosted or reduced

    111. Q Chart Q Setting Bandwidth 0.7 2 Octaves 1.0 1 1/3 Octaves 1.4 1 Octave 2.8 1/2 Octave

    112. Equalizer Types Graphic equalizer, Several varieties Shelving (highpass-lowpass) High or low cut or boost Parametric, Boost, cut, center freq & Q

    113. Speech Characteristics Cover three main frequency bands Fundamentals Vowels Consonants

    114. Fundamentals 125 250 Hz Essential for voice quality (who is speaking) 315 500 Hz also important to voice quality

    115. Vowels Contain the maximum energy & Power of the voice 350 Hz 2,000 Hz 630 1 KHz Important for natural sound

    116. Consonants 1,500 4,000 Hz contain little energy but are essential to intelligibility 1.25 8 KHz governs the clarity of vocals

    117. Energy 63 500 Hz contain 60% power and 5% intelligibility 500 1 KHz contain 35% power and 35% intelligibility 1K 8 KHz 5% power and 60% intelligibility

    118. EQ ProblemVocals Boost 100 250 Boomy Cut 150 500 Boxy, Hollow Cut 500 1 KHz hardness Boost 1 3 KHz metallic Cut 2 5 KHz lifeless Boost 4 10 KHz gritty, sibilance

    119. General Tips Be sure level is correct before EQ (dont use EQ to make up for low level) Boost less Cut more Do not boost fundamentals Avoid boosting the same frequency for 2 instruments

    120. General Tips Do not use EQ to make-up for poor microphone placement Keep track of what works best for your mixes. Use notes as starting point to save time during sound check

    121. Equalization Primer Follow link for more information about equalization.

    122. Review Week 4

    123. Magnetic Tape Back coat Plastic base Binder Magnetic coating

    125. Magnetic Tape Several different coatings Iron oxide Chromium dioxide Cobalt Doped Metal

    126. Magnetic Tape Properties Not detailed in this class Coercivity, Retentivity, Sensitivity, Print through, Dropout, and many more

    127. Recording Process Recording is non-linear at audio frequencies Bias current is needed to make recording linear Bias adjustment depends on type of tape

    128. Bias Frequency Around 100 KHz Applied to Erase Head Modulated by Audio

    129. End of week 5 End of week 5

    130. Mix Bus Common point where multiple signals are combined Summing point

    131. Attenuators Used to reduce signal level Many types Gain controls do not do the same thing

    132. Refer to EPM Mixer Guide Functional description Block Diagram How to use some functions

    133. Review Week 5

    134. Digital Audio A to D Process Storage D to A Process

    135. A to D Process Sampling Rate How many times per second is the analog signal looked at CD is 44,100/Sec

    136. Sampling vs Frequency Sampling rate needs to be twice the frequency of the highest audio frequency needed

    138. Anti-aliasing A low pass filter us used to limit high frequencies prior to sampling

    139. Number Systems Decimal Binary Others; octal, Hexadecimal, etc.

    140. Weighting

    141. 16 bit Binary 1-1, 2-2, 3-4, 4-8, 5-16, 6-32, 7-64, 8-128, 9-256 10-512, 11-1024, 12-2048, 13-4096, 14-8192, 15-16384, 16-32768, 17-65536

    142. Quantization The Value of each sample Two 8 Bit words (16 bits) yields 65,536 graduations (used for each CD channel)

    145. The D to A Process Demodulation Error Correction D to A Conversion Sample and Hold Low Pass Filter

    146. Demodulation Restores the recorded signal to original ones and zeros

    147. Error Correction Compensates for errors introduced during the recording process

    148. D to A Conversion Electronic process that converts digital numbers (samples) into analog voltage (current)

    149. Sample and Hold Circuits that remove Switching Glitches that appear after D to A processing

    150. Low Pass Filtering A circuit that does the final smoothing of the analog signal and removes any high frequency noise

    151. File Conversion Free tools for both Mac & PC Advanced tools for purchase

    152. Wiring Considerations Most digital connections use standard XLR connectors wired the same as balanced audio Do not bundle/run with audio cabling

    153. Wiring Considerations Most MIDI hardware uses DIN-5 pin connections Pins 4 & 5 carry digital signal Pin 2 is shield 50 ft maximum length