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analysis of of sound

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2. FREE FIELDI = W/4r2at r = 1 m: LI = 10 log I/10-12 = 10 log W/10-12 10 log 4p= LW - 11 3. HEMISPHERICAL FIELD I = W/2pr2at r = l m LI = LW - 8 Note that the intensity I 1/r2 for both free and hemispherical fields; therefore, LI decreases 6 dB for each doubling of distance 4. SOUND PRESSURE LEVEL Our ears respond to extremely small pressure fluctuations pIntensity of a sound wave is proportional to the sound Pressure squared:c 400 I = p2 /c = density (1.21kg/m3) c = speed of sound (343 m/s)We define sound pressure level: Lp = 20 log p/p0p0 = 2 x 10-5 Pa (or N/m2) (or SPL) 5. TYPICAL SOUND LEVELS 6. MULTIPLE SOURCES Example:Two uncorrelated sources of 80 dB each will produce a sound level of 83dB (Not 160 dB) 7. MULTIPLE SOURCES What we really want to add are mean-squareaverage pressures (average values of p2)This is equivalent to adding intensitiesExample: 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 8. SOUND PRESSURE and INTENSITY 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 9. FOUR ATTRIBUTES USED TO DESCRIBE A SOUND:LoudnessPitchTimbreDuration 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 PHYSICALPARAMETERS that we can MEASURE OBJECTIVELYIs an important problem in PSYCHOACOUSTICS 10. DEPENDENCE OF SUBJECTIVE QUALITIES OFSOUND ON PHYSICAL PARAMETERS 11. LOUDNESS LEVELContours of equal loudness are labeled phonsAt 1000 Hz, Loudness Level = Lp 12. PLOT YOUR OWN FREQUENCY RESPONSEASSIGNMENT: Plot your own frequency response curves by usingwww.phys.unsw.edu.au/~jw/hearing.html 13. HOW DOESLOUDNESSDEPEND ON FREQUENCY? 14. LOUDNESS SCALING 15. LOUDNESS RESPONSE OF THE EAR 16. LOUDNESS OF COMPLEX TONES Loudness depends mainly on SOUND PRESSURE.but it also depends on FREQUENCY, SPECTRUM and DURATION 17. DEPENDENCE OFLOUDNESS ONBANDWIDTH CRITICAL BANDS 18. LOUDNESS OF COMBINED SOUNDS 19. JUST NOTICEABLE LEVEL DIFFERENCE 20. LEVEL INCREMENT NEEDED TO DOUBLE LOUDNESS 21. RANGE OF FREQUENCY AND INTENSITYOF THE EAR 22. MUSICAL DYNAMICS AND LOUDNESS 23. HOW DOES LOUDNESS DEPEND ONPARTIAL MASKING? 24. HOW DOES LOUDNESS DEPEND ON DURATION? 25. LOUDNESS RECRUITMENT UNUSUALLY RAPID GROWTH OF LOUDNESSABOVE A CERTAIN THRESHOLDGENERALLY ASSOCIATED WITH HEARING LOSS, BUT NORMAL LISTENERS EXPERIENCE IT FOR TONES OF VERY HIGH OR VERY LOW FREQUENCY 26. MONAURAL vs BINAURAL LOUDNESSFOR SOFT SOUNDS (~20dB) BINAURAL LOUDNESS EXCEEDS MONAURAL LOUDNESSBY A FACTOR OF 2(CORRESPONDS TO L = 8dB)FOR LOUD SOUNDS (~80dB) BINAURAL LOUDNESS EXCEEDS MONAURAL LOUDNESS BY A FACTOR ~/.4 (CORRESPONDS TO L = 6dB) Zwicker & Fastl (1990) 27. INTENSITY DISCRIMINATION AND CODING AT LOW LEVELS, INTENSITY CHANGES CAN BESIGNALLED BOTH BY CHANGES IN FIRING RATES OF NEURONS AT THE CENTER OF THE EXCITATION PATTERN AND BY THE SPREADING OF THE EXCITATIONPATTERN (TO INCLUDE MORE NEURONS)AT HIGH LEVELS, MOST NEURONS AT THE CENTER OF THE EXCITATION PATTERN ARE SATURATED, BUTINTENSITY CHANGES ARE SIGNALLED BY CHANGES IN FIRING RATES AT THE EDGES. AN INCREASE IN LEVEL ALSO MAY BE SIGNALLEDBY INCREASED PHASE LOCKING TO THE TONE WHICHRESULTS IN TEMPORAL REGULARITY OFNEURAL FIRINGS