Human hearing

Phys1061, S.Boyd 1

Human hearingHuman hearing

Limits, the human ear, and issues Limits, the human ear, and issues of perceptionof perception

SylkeSylke Boyd, Univ. of MinnesotaBoyd, Univ. of Minnesota

Physical CharacteristicsPhysical Characteristics

�� Frequency range: 20 Hz … 20 kHzFrequency range: 20 Hz … 20 kHz

�� Factor of 1000Factor of 1000

�� Intensity range: 10Intensity range: 10--1212 to 1 W/mto 1 W/m22

�� Factor of 10Factor of 101212

�� Filtering of informationFiltering of information

Physical characteristicsPhysical characteristics

Graphics: Rossing, Moore & Wheeler, The Science of Sound, 3rd Ed.

Psychophysics:Psychophysics:

�� objective and quantitative study of the relation objective and quantitative study of the relation of physical stimuli and sensory perceptionsof physical stimuli and sensory perceptions

Pressure fluctuations

Middle Ear:

Transformation into mechanical and then electrical signals

Processing: sorting, selection,recognition

StructureStructureof theof thehumanhuman

earear

Important parts of the CochleaImportant parts of the Cochlea

�� Oval windowOval window

�� Scala vestibuli (filled Scala vestibuli (filled with fluid)with fluid)

�� Scala timpaniScala timpani

�� Round windowRound window

�� Basiliar membraneBasiliar membrane

�� Organ of CortiOrgan of Corti

�� Auditory nerveAuditory nerve

Human hearing

Phys1061, S.Boyd 2

Mechanism of signal transportMechanism of signal transport

Hall, Musical Acoustics, 3rd Ed.

Lever action of ossiclesLever action of ossicles

Small displacement over large area becomes Small displacement over large area becomes large displacement over small arealarge displacement over small area

Just noticeable differencesJust noticeable differences

�� At which frequency difference do two At which frequency difference do two tones sound different to us?tones sound different to us?

200/201 Hz200/202 Hz200/203 Hz

2000/2002 Hz2000/2003 Hz2000/2004 Hz2000/2006 Hz2000/2008 Hz

2000/2002 Hz2000/2003 Hz2000/2004 Hz2000/2006 Hz2000/2008 Hz

Simultaneous soundsSimultaneous sounds

�� At which difference in frequency can we At which difference in frequency can we hear two distinct sounds?hear two distinct sounds?

1000 Hz combined with …

990 Hz 1010 Hz

980 Hz 1020 Hz

950 Hz 1050 Hz

900 Hz 1100 Hz 1200 Hz 1300 Hz800 Hz700 Hz

How are sounds resolved?How are sounds resolved?How are sounds resolved?How are sounds resolved?

�� Critical band: region on basilar membrane Critical band: region on basilar membrane for reception of a pure tonefor reception of a pure tone

�� If critical bands overlap, only a single tone If critical bands overlap, only a single tone is heardis heard

�� The (relative) critical band is larger at low The (relative) critical band is larger at low frequencies.frequencies.