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Human hearing. Limits, the human ear, and issues of perception. Physical Characteristics. Frequency range: 20 Hz … 20 kHz Factor of 1000 Intensity range: 10 -12 to 1 W/m 2 Factor of 10 12 Filtering of information. Physical characteristics.
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Human hearing Limits, the human ear, and issues of perception
Physical Characteristics • Frequency range: 20 Hz … 20 kHz • Factor of 1000 • Intensity range: 10-12 to 1 W/m2 • Factor of 1012 • Filtering of information
Physical characteristics Graphics: Rossing, Moore & Wheeler, The Science of Sound, 3rd Ed.
Middle Ear: Transformation into mechanical and then electrical signals Psychophysics: • objective and quantitative study of the relation of physical stimuli and sensory perceptions Processing: sorting, selection, recognition Pressure fluctuations
Important parts of the ear Outer Ear: • Auditory canal • Ear drum Middle ear: • Ossicles: hammer (malleus), anvil (incus), stirrup (stapes) Inner Ear • Cochlea • Auditory nerve
Important parts of the Cochlea • Oval window • Scala vestibuli (filled with fluid) • Scala timpani • Round window • Basiliar membrane • Organ of Corti • Auditory nerve
Mechanism of signal transport Hall, Musical Acoustics, 3rd Ed.
Lever action of ossicles Small displacement over large area becomes large displacement over small area
Hearing loss • Conduction deafness: reduced mobility of ossicles due to vibrous tissue (i. e. from repeated otitis) • Nerve deafness: deterioration of hair cells or nerve (also age-related presbycusis) • Can be distinguished through bone conduction
Just noticable differences • At which frequency difference do two tones sound different to us? 200/201 Hz 200/202 Hz 200/203 Hz 2000/2002 Hz 2000/2003 Hz 2000/2004 Hz 2000/2006 Hz 2000/2008 Hz 2000/2002 Hz 2000/2003 Hz 2000/2004 Hz 2000/2006 Hz 2000/2008 Hz
Simultaneous sounds • At which difference in frequency can we hear two distinct sounds? 1000 Hz combined with … 700 Hz 800 Hz 900 Hz 990 Hz 1010 Hz 1100 Hz 1200 Hz 1300 Hz 980 Hz 1020 Hz 950 Hz 1050 Hz
How are sounds resolved? • Critical band: region on basiliar membrane for reception of a pure tone • If critical bands overlap, only a single tone is heard • The critical band is larger at low frequencies.