This material is based on work supported by the National Science Foundation under CCLI Grant DUE 0717743,
Jennifer Burg PI, Jason Romney, Co-PI.
4 Chapter 4 Sound Perception and Acoustics .........................................2
4.1 Concepts ..................................................................................2
4.1.1 Acoustics ............................................................................2
4.1.2 Psychoacoustics ...................................................................2
4.1.3 Objective and Subjective Measures of Sound ........................... 2
4.1.4 Units for Measuring Electricity and Sound ............................... 3
4.1.5 Decibels ..............................................................................5
4.1.5.1 Why Decibels for Sound? .................................................5
4.1.5.2 Various Usages of Decibels ..............................................8
4.1.5.3 Peak Amplitude vs. RMS Amplitude .................................11
4.1.6 Sound Perception ...............................................................14
4.1.6.1 Frequency Perception ....................................................14
4.1.6.2 Critical Bands...............................................................17
4.1.6.3 Amplitude Perception ....................................................20
4.1.7 The Interaction of Sound with its Environment ...................... 22
4.1.7.1 Absorption, Reflection, Refraction, and Diffraction ............ 23
4.1.7.2 Reverberation, Echo, Diffusion, and Resonance ................ 25
4.2 Applications ............................................................................27
4.2.1 Working with Decibels ........................................................27
4.2.1.1 Real-World Considerations .............................................27
4.2.1.2 Rules of Thumb ............................................................28
4.2.1.3 Determining Power and Voltage Differences and Desired
Changes in Power Levels .............................................................28
4.2.1.4 Converting from One Type of Decibels to Another ............. 30
4.2.1.5 Combining Sound Levels from Multiple Sources ................ 31
4.2.1.6 Inverse Square Law ......................................................31
4.2.2 Acoustic Considerations for Live Performances ....................... 33
4.2.2.1 Potential Acoustic Gain (PAG) ........................................33
4.2.2.2 Checking and Setting Sound Levels ................................ 35
4.2.2.3 Impulse Responses and Reverberation Time .................... 37
4.2.2.4 Frequency Levels and Comb Filtering .............................. 40
4.2.2.5 Resonance and Room Modes ..........................................45
4.2.2.6 The Precedence Effect ...................................................48
4.2.2.7 Effects of Temperature ..................................................50
4.2.2.8 Modifying and Adapting to the Acoustical Space ............... 51
4.2.3 Acoustical Considerations for the Recording Studio ................. 53
4.3 Science, Mathematics, and Algorithms .......................................56
4.3.1 Deriving Power and Voltage Changes in Decibels ................... 56
4.3.2 Working with Critical Bands .................................................58
4.3.3 A MATLAB Program for Equal Loudness Contours ................... 59
4.3.4 The Mathematics of the Inverse Square Law and PAG Equations
61
4.3.5 The Mathematics of Delays, Comb Filtering, and Room Modes . 63
4.4 References .............................................................................65
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