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SOUND PRESSURE, POWER AND LOUDNESS

SOUND PRESSURE, POWER AND LOUDNESS. MUSICAL ACOUSTICS. Science of Sound Chapter 6. DECIBEL SCALES. FREE FIELD. I = W/4πr 2. at r = 1 m: L I = 10 log I/10 -12 = 10 log W/10 -12 – 10 log 4 p = L W - 11. HEMISPHERICAL FIELD. I = W/2 p r 2. at r = l m L I = L W - 8.

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SOUND PRESSURE, POWER AND LOUDNESS

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  1. SOUND PRESSURE, POWER AND LOUDNESS MUSICAL ACOUSTICS Science of Sound Chapter 6

  2. DECIBEL SCALES

  3. FREE FIELD I = W/4πr2 at r = 1 m: LI = 10 log I/10-12 = 10 log W/10-12 – 10 log 4p = LW - 11

  4. HEMISPHERICALFIELD I = W/2pr2 at r = l m LI = LW - 8 Note that the intensity I α 1/r2 for both free and hemispherical fields; therefore, LI decreases 6 dB for each doubling of distance

  5. SOUND PRESSURE LEVEL Our ears respond to extremely small pressure fluctuations p Intensity of a sound wave is proportional to the sound Pressure squared: ρc ≈ 400 I = p2 /ρcρ = density c = speed of sound We define sound pressure level: Lp = 20 log p/p0 p0 = 2 x 10-5 Pa (or N/m2) (or SPL)

  6. TYPICAL SOUND LEVELS

  7. MULTIPLE SOURCES Example:Two uncorrelated sources of 80 dB each will produce a sound level of 83dB (Not 160 dB)

  8. MULTIPLE SOURCES What we really want to add are mean-square average pressures (average values of p2) This is equivalent to adding intensities Example: 3 sources of 50 dB each Lp = 10 log [(P12+P22+P32)/P02] = 10 log (I1 + I2 + I3)/ I0) = 10 log I1/I0 + 10 log 3 = 50 + 4.8 = 54.8 dB

  9. Sound pressure level is measured with a sound level meter (SLM) Sound intensity level is more difficult to measure, and it requires more than one microphone In a free field, however, LI ≈ LP SOUND PRESSURE and INTENSITY

  10. Loudness • Pitch • Timbre • Duration FOUR ATTRIBUTES USED TO DESCRIBE A SOUND: EACH OF THESE DEPENDS ON ONE OR MORE PHYSICAL PARAMETERS THAT CAN BE MEASURED: • Sound pressure • Frequency • Spectrum • Duration (measured) • Envelope Relating the SUBJECTIVE QUALITIES to the PHYSICAL PARAMETERS that we can MEASURE OBJECTIVELY Is an important problem in PSYCHOACOUSTICS

  11. DEPENDENCE OF SUBJECTIVE QUALITIES OF SOUND ON PHYSICAL PARAMETERS

  12. LOUDNESS LEVEL Contours of equal loudness are labeled phons At 1000 Hz, Loudness Level = Lp

  13. PLOT YOUR OWN FREQUENCY RESPONSE ASSIGNMENT: Plot your own frequency response curves by using www.phys.unsw.edu.au/~jw/hearing.html

  14. HOW DOES LOUDNESS DEPEND ON FREQUENCY?

  15. LOUDNESS SCALING

  16. LOUDNESS RESPONSE OF THE EAR

  17. LOUDNESS OF COMPLEX TONES Loudness depends mainly on SOUND PRESSURE. but it also depends on FREQUENCY, SPECTRUM and DURATION

  18. DEPENDENCE OF LOUDNESS ON BANDWIDTHCRITICAL BANDS

  19. LOUDNESS OF COMBINED SOUNDS

  20. JUST NOTICEABLE LEVEL DIFFERENCE

  21. LEVEL INCREMENT NEEDED TO DOUBLE LOUDNESS

  22. RANGE OF FREQUENCY AND INTENSITY OF THE EAR

  23. MUSICAL DYNAMICS AND LOUDNESS

  24. HOW DOES LOUDNESS DEPEND ON PARTIAL MASKING?

  25. HOW DOES LOUDNESS DEPEND ON DURATION?

  26. LOUDNESS RECRUITMENT UNUSUALLY RAPID GROWTH OF LOUDNESS ABOVE A CERTAIN THRESHOLD GENERALLY ASSOCIATED WITH HEARING LOSS, BUT NORMAL LISTENERSEXPERIENCE IT FOR TONES OF VERY HIGH OR VERY LOW FREQUENCY

  27. MONAURAL vs BINAURAL LOUDNESS FOR SOFT SOUNDS (~20dB) BINAURAL LOUDNESS EXCEEDS MONAURAL LOUDNESS BY A FACTOR OF 2 (CORRESPONDS TO ΔL = 8dB) FOR LOUD SOUNDS (~80dB) BINAURAL LOUDNESS EXCEEDS MONAURAL LOUDNESS BY A FACTOR ~/.4 (CORRESPONDS TO ΔL = 6dB) Zwicker & Fastl (1990)

  28. INTENSITY DISCRIMINATION AND CODING AT LOW LEVELS, INTENSITY CHANGES CAN BE SIGNALLED BOTH BY CHANGES IN FIRING RATES OF NEURONS AT THE CENTER OF THE EXCITATION PATTERN AND BY THE SPREADING OF THE EXCITATION PATTERN (TO INCLUDE MORE NEURONS) AT HIGH LEVELS, MOST NEURONS AT THE CENTER OF THE EXCITATION PATTERN ARE SATURATED, BUT INTENSITY CHANGES ARE SIGNALLED BY CHANGES IN FIRING RATES AT THE EDGES. AN INCREASE IN LEVEL ALSO MAY BE SIGNALLED BY INCREASED PHASE LOCKING TO THE TONE WHICH RESULTS IN TEMPORAL REGULARITY OF NEURAL FIRINGS

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