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4. The Ear and the Perception of Sound ( Psychoacoustics )

1. 4. The Ear and the Perception of Sound ( Psychoacoustics ). Updated May 13, 2012. 2. Outline. Structure of the Ear Perception of Loudness Perception of Pitch References. 3. Introduction. Psychoacoustics is the study of subjective human perception of sounds. 4.

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4. The Ear and the Perception of Sound ( Psychoacoustics )

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  1. 1 4. The Ear and thePerception of Sound(Psychoacoustics) Updated May 13, 2012

  2. 2 Outline • Structure of the Ear • Perception of Loudness • Perception of Pitch • References

  3. 3 Introduction Psychoacoustics is the study of subjective human perception of sounds.

  4. 4 A. The Structure of the Ear The length of the auditory canal has been greatly exaggerated

  5. 5 A.1 Outer Ear Amplifies Sound Auditory canal is a resonator at approximately 2000 to 5000 Hertz.

  6. 6 A.2 The Middle Ear • The bones (ossicles) of the middle ear form a lever which “amplifies” the displacement by a factor of 3x. • The stirrup transfers the force to the much smaller area of the oval window, resulting in 10 to 30 x increase in pressure level • Overall the sound is amplified by as much as 1000x or 30 dB

  7. 7 A.3 Inner Ear Senses Sound Reference: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/place.html#c1 Over 20,000 hair cells!

  8. 8 B. Perception of Loudness • Discrimination of Loudness • The Phon (Equal loudness) • The Sone & Perceived Loudness

  9. 9 1a. JND: Just Noticeable Difference is 1dB • Reference: http://www.phys.unsw.edu.au/jw/dB.html

  10. 10 1b Discrimination of Loudness • jnd = “just noticeable difference” • The ear’s “jnd” for Loudness is approximately 1 dB • Or, sound must be 30% louder in intensity for us to just notice that it is louder. • This depends somewhat on frequency (pitch) and loudness (intensity). We have trouble distinguishing changes in loudness for very the very loud or the very soft sounds

  11. 11 1c. Smaller than JND (7% change) • Reference: http://www.phys.unsw.edu.au/jw/dB.html

  12. 12 2a. Threshold of Hearing & Age (Presbycusis) Note “Sound Pressure dB” (or SPLdB) is approximately half regular “energy” decibels (dB).

  13. 13 2a. Hearing Threshold • The ear can hear as small as 10-12 Watts/m2(one trillionth of a watt per square meter)( 0.000,000,000,001 Watt/m2 ) • Example: you might be able to hear someone talking half a mile away under ideal circumstances • Intensity is proportional to thesquare of the pressure amplitudeMinimum ear can hear is 0.000,02 Pascals(Atmospheric pressure is 100,000 Pascal)

  14. 14 2b Phon & Equal Loudness Level Hearing Threshold changes with frequency. The “Phon” scale is a frequency-adjusted decibel scale based upon perception. Hence 0 Phon is always the threshold, and 10 Phon “sounds” like its 10 dB louder. The Fletcher-Munson curves are a way of mapping the dB of a pure tone to the perceived loudness level in phons.

  15. 15 2c Steven’s “Phon” • Ear is found NOT to exactly follow Fechner’s logarithmic law (i.e. decibel scale). • Stanley Smith Stevens (1906–1973)proposes “Phon”, which matches dB at 1000 Hertz. • 0 Phon is the threshold of hearing, which is adjusted for frequency (for example, at 100 Hertz,0 Phon is equivalent to 35 dB) • Perception of loudness is also frequency dependent. • 1000 Hertz: 10 dB is perceived as 10 phon • 100 Hertz: 10 dB is perceived as 16 phon

  16. 16 3a. Sone Scale (Steven’s Power Law) • 1936 Stevens proposes the “Sone” scale is closer to perceived loudness (2 Sones will “sound” to the ear as if it is twice as loud as 1 Sone) • A multiplicative factor of 2x in Sone corresponds to 10 Phon. • 10 people singing will only appear to be 2x as loud as a soloist! • 1/16 Sone is threshold of hearing • 0.17 Sone is a whisper • 4 Sone is talking • 256 Sone is maximum safe level • 2048 Sone is jet engine (ear damage) =================== Phon Sone ____________________ 0 0.0625 10 0.125 20 0.25 30 0.5 40 1 50 2 60 4 70 8 80 16 90 32 ===================

  17. 17 C. Perception of Pitch • Range of Hearing • Pitch Discrimination and jnd • Uncertainty Principle

  18. 18 1a Range of Hearing Humans can hear from 16 to 20,000 Hertz (In terms of music, this is about 10 octaves) Piano only goes from 27.5 to 4186 Hertz

  19. 19 1b Test Hearing • High Frequency Test • http://audiocheck.net/audiotests_frequencycheckhigh.php • Low Frequency Test • http://audiocheck.net/audiotests_frequencychecklow.php

  20. 20 1c. Test your Hearing http://www.phys.unsw.edu.au/jw/hearing.html

  21. 21 2a. Pitch Discrimination • At 1000 Hz, the “jnd” is about 1 Hz (0.1%) • At 4000 Hz, the “jnd” is about 10 Hz (0.25%) • Above 10,000 Hz, our discrimination is terrible.(Most music is in range of 30 to 4000 Hertz) • We can distinguish approximately 5000 different tones

  22. 22 2b. Beats • Two tones closer than 15 Hertz we hear as a “fused” tone (average of frequencies) with a “beat”. 400 401 400 403 400 410 400 420 400 440 400 450 400 480 Demo: http://www.phys.unsw.edu.au/jw/beats.html#sounds

  23. 23 2c. Combination Tones • When tones are far enough apart we hear them as two distinct tones • We also hear differenceand sum tones thatare not really there(Tartini Tones 1714) Demo: http://www.phys.unsw.edu.au/jw/beats.html#Tartini

  24. 24 3a. Pitch Uncertainty • The longer time you have T to measure a tone, the smaller your uncertainty in its frequency f • Uncertainty Equation: f T  1 • So to distinguish a 400 and 401 Hertz tone you would need 1 second http://www.phys.unsw.edu.au/jw/uncertainty.html

  25. 25 3b. Pitch & Amplitude • Tones above 2000 Hz appear to increase in pitch with increase in dB • Tones below 2000 Hz appear to decrease in pitch with increase in dB • At 4000 Hz, increases 20 cents /30 dB (14%) • At 1000 Hz, decreases 10 cents/30 db (7%) *An octave (doubling of frequency) is divided into 1200 cents. The ear can discriminate a frequency difference of about 5 cents, so these effects are small!

  26. 26 D. Notes/References • http://en.wikipedia.org/wiki/Phon • http://en.wikipedia.org/wiki/Sound_pressure_level • http://en.wikipedia.org/wiki/Weber-Fechner_law • http://en.wikipedia.org/wiki/Stevens%27_power_law • http://www.sfu.ca/sonic-studio/handbook/Sone.html • http://www.phys.unsw.edu.au/jw/dBNoFlash.html • http://www.phys.unsw.edu.au/jw/uncertainty.html • http://www.phys.unsw.edu.au/jw/beats.html • http://audiocheck.net/audiotests_frequencycheckhigh.php • http://audiocheck.net/audiotests_frequencychecklow.php • Demos: • http://www.isvr.soton.ac.uk/SPCG/Tutorial/Tutorial/Tutorial_files/Web-hearing-Shepard.htm

  27. Things to do • Fechner’s law was done in previous topic. • Part A: need more on number of hairs in ear, quantitative • Part B: at what level do hairs break? • Need a phon/sone table • Upper range of hearing vs age • Range of hearing from past classes • Part C: critical bands?

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