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Audio-Visual Engineering - Properties of Musical Sound...

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Properties of Musical Sound Subjective Objective Pitch Frequency Volume Amplitude/power/intensity Timbre Overtone content/spectrum Duration in beats Duration in time
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Direct Sound Sound waves that travel directly from the source to the listener. Direct Sound intensity attenuates with the distance according to the inverse square law . 2 Dist K I = For example, doubling the distance will result in an attenuation of 4 times, or dB 6 -
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Early (first order) Reflection Sound waves that travel to the listener after reflecting “once” from the environment (mainly walls). Early reflection within 35ms from direct sound reinforce the latter. According to Beranek who study 54 concert halls, “intimate” effect was felt with early reflections of less than 20ms. In large halls, suspended reflectors are employed to provide early reflection to center seats.
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Reverberation (second to higher order reflection) Sound waves that travel to the listener after reflection of first-order-reflection. Reverberation will decay with time as sound energy is absorbed by the enviroment. Reverberation time is the duration for the sound pressure to drop to 60dB of its initial level, in general for the frequency range of 500-1000Hz, ( 29 ( 29 2 3 s m urface room Total m volume Room T R = High frequency signals are absorbed more quickly in air than low ones, reverberation time is hence shorter.
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Microphone Dynamic Magnetic Induction A Classical Ribbon Microphone Magnet Coil Ribbon diaphragm Simple Economical Robust
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Microphone Condenser Capacitor Transducer A Condenser Microphone Complicated Expensive Sharper transient Phantom power Current
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Magnitude of a microphone’s response to pressure changes imposed at different directions. 0o 30o 60o 90o 330o 300o 270o 240o 210o 180o 150o 120o 0.25 0.50 0.75 1.0
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0o 30o 60o 90o 330o 300o 270o 240o 210o 180o 150o 120o 0.25 0.50 0.75 1.0 Omnidirectional 1 = ρ
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0o 30o 60o 90o 330o 300o 270o 240o 210o 180o 150o 120o 0.25 0.50 0.75 1.0 Bidirectional (figure-eight) ( 29 θ ρ cos =
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0o 30o 60o 90o 330o 300o 270o 240o 210o 180o 150o 120o 0.25 0.50 0.75 1.0 Standard cardioid ( 29 θ ρ cos 5 . 0 5 . 0 + =
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0o 30o 60o 90o 330o 300o 270o 240o 210o 180o 150o 120o 0.25 0.50 0.75 1.0 Supercardioid ( 29 θ ρ cos 63 . 0 37 . 0 + =
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0o 30o 60o 90o 330o 300o 270o 240o 210o 180o 150o 120o 0.25 0.50 0.75 1.0 Subcardioid ( 29 θ ρ cos 25 . 0 75 . 0 + =
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XY (coincident pair) Microphone Recording 90 -135 Top view Front view Two identical cardioids aimed across each other at 90 to 135 , 12 inches or less apart Extremely mono-compatible, moderate stereo effect. Localization of sound source based on difference in amplitude. e.g., if L > R, the source seems to be closer to the left side.
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Blumlein coincident Microphone Recording 90 Top view Front view Two identical “figure 8” microphones placed at 90 , one directly on top of the other Create by Alan Blumlein, provides precise stereo imaging from sound sources at front and reverberation from rear. L R
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Near coincident Microphone Recording 90 -135 Top view ORTF (Office de Radio Television Francaise), 2 cardioids spaced 17cm apart at 110o apart.
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