Acoustics and Psychoacoustics

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• Acoustics- science of sound wave behavior Psychoacoustics- study with human perception of acoustics

1. Life Cycle of Sound

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   • Direct: Sound that reaches the ear first Early Refections: indirect sound, same sound reflected off nearby surfaces (loudness, fullness, room size) Reverberation: Multiple early reflections becoming smaller (creates spaciousness)
   1. Spatial/Binaural Hearing

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      • Sound is omni-directional 360 degrees 2 ears to hear direction of sound brain process time diff and intensity from one ear to other stereo vs. surround illusion vs real thing
      1. Reverb vs. Echo

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         • Reverb- densely spaced, multiple reps of sound Echo- delayed, repeat of sound, delayed by 35ms or more
         1. Studio

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            • RT time- sound to drop 60dB after steady state Live room reverb decay 1 sec or more become live Dry dead room- lil/quick reverb decay .5 sec or less too add liveness 500-2KHz & reverb 1-2 sec.
            • Design Noise Criteria- HVAC mechanical noise in buildings, audio equip. 10-20 range Isolation- Sound transmission class (STC) loss through paritions or walls
            • Rooms LxWxH Parallel surfaces rectangle rooms no square rooms
            1. Sound
               1. Mic tecniques

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                  • 1.close miking control sound, tame leak 2.distant miking on axis-placing mic perpediclar to source off-miking father away from source to capture sound
                  1. Close miking

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                     • closer the mic to source, drier, detailed, intimate higher frequencies more directional, lower frequencies are omni directional more mics can add more sound to phasing problem large diaphragm- low frequency small diaphragm-high frequency
                  2. stereo

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                     • played in both speakers create illusion stereo- mono sounds  and differences equilateral triangle left to right created by position of listener
                     • increased by mics closer to sources acoustic barriers directional mics spread sound sources farther apart
                     1. stereo miking
                  3. mic types
                     1. mic characteristics

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                        • polar response pattern- direction of which mic hears sound (direction sensitivity) Omnidirectional- sound is picked up an almost all directions, bidirectional- front and rear least on sides cardioid- at front and sides frequency response- the range of frequencies that it porduces at an equal level, within a margin of +3dB
                        1. capacitor

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                           • are sensitive. common used mics are winscreen pop filter, shock mounts 2 switches for flexibility on sound- -10dB pad to reduce input level and control distortion to pre-amp, bass roll-off usually at about 80hzto control proximity effect difference between capacitor and moving coil- cap needs power to operate, moving coil needs magnetic variations to operate
                           1. ribbon

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                              • characteristics more fragile, more expensive, small output level, can't take high SPL levels
                              1. condensor

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                                 • most expensive most sensitive sensitive to high frequency handle to high SPL better detail
                     2. mic modeler

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                        • not actual mic, stimulator that can be added to DAW as plug in
                        1. mic accessories

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                           • windscreens and pop filteres are design to deal with distortion that results from blowing sounds caused by breathing and wind. windscreens are mounted externally and reduce the distortion from blowing and popping but rarely eliminate from particular sound pop filters- aka blast filters are mainly found in moving coil, newwe ribbon, and some capacitor
                           1. shock mounts

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                              • a device suspended and mechanically isolates mic from stand
                              1. cables

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                                 • balanced line consisitng of to conductors and a shield- or an unbalanced line consisting of one conductor with the sheild serving as the second conductor
                     3. mic etc.

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                        • mic sensitivity- higher the frequency the more diectional it becomes, lower the frequency, less direction regarless of pickup pattern
                        1. ribbon

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                           • more fragile more expensive more sensitive small output level cant take high spl levels
                           1. condenser

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                              • most expensive most sensitive sensitive high freq handle high SPL better detail
                        2. polar patter response

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                           • directional sensitivity omnidirectional- in all directions bidirectional- front and rear cardioid- at front and front sides
               2. Enter text here
               3. sound response

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                  • frequency response- the range of frequencies that reproduces at equal level within margin of +3dB
                  1. overload limit

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                     • will distort when levels are too high moving coil and capacitor are not as vulnerable
                     1. max sound pressure level

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                        • level where mic signals begin to distort. if mic has max SPL at 120dB will distort. 120dB is good 135dB is very good 150 is excellent total harmonic distortion- compares output signal with input, lower the percentage the better
                        1. sensitivity

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                           • measures the voltage that mic produces- relationship in decibles to voltage, how loud a mic is capacitor are loudest ribbon are quiet ibbon and small coil low sensitivity- (-85 dbv) larger have med sensitivity (-75 dbv) capacitor (-65 dbv) high sensitivity
                           1. self noise

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                              • equivalent noise level SPL create same voltage as electrical noise measured in dB-SPL, A weighted Fair noise- around 40 db-SPL (a) good rating is 30 dB-spl (a) and excellent 20 dB-spla (a) or less
                              1. signal to noise

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                                 • signal power to noise power measured in decibles. the higher the s/n the less obtrusive the noise 64db is fair 74 is good 84db and higher is excellent
                                 1. proximity effect

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                                    • placed close to sound source, bass frequencies increase in level relative  to midrange and treble frequencies
                                    1. hum

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                                       • to minimize- typically produced to stray ac magnetic fields 50-60hZ using balanced mic cables and connectors, twisted pair mic cables with good shoeld coverage, braided shield, humbuck coil
            2. mixers/ consoles/control

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               • most common acoustic treatment- bass traps, diaphrgmantic aborbers studio project- first consideration is the music style bell-berliner telephone the transformer
            3. mixers

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               • input section- incoming signal from mic such as cd, recorder output section- all input signals are combined for further routing to recording or transmission monitor section- means to hear the output signal through headphones
   2. misc

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      • mic positions- tyoe of music, quality of insruments, acoustics, number of musicians transient- sound that begins fast attack and quick decay 2,3 pins mic reverse- out of polarity out of phase studio for sound in mic pickup control room listening to loud speakers first cardioid cap mic 1932 neumann vibrating body- resonance electric flow- current subwoofer- non-directional and omni directional neumann began in 1928 first recording 1931