Human hearing

1
Human hearing

• Limits, the human ear, and issues of perception

2
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

3
Physical characteristics
Graphics Rossing, Moore Wheeler, The Science
of Sound, 3rd Ed.
4
Psychophysics

• objective and quantitative study of the relation
  of physical stimuli and sensory perceptions

Processing sorting, selection, recognition
Pressure fluctuations
5
Structure of the human ear
6
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

7
Important parts of the Cochlea

• Oval window
• Scala vestibuli (filled with fluid)
• Scala timpani
• Round window
• Basiliar membrane
• Organ of Corti
• Auditory nerve

8
Mechanism of signal transport
Hall, Musical Acoustics, 3rd Ed.
9
Lever action of ossicles

• Small displacement over large area becomes large
  displacement over small area

10
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

11
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
12
Simultaneous sounds

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

1000 Hz combined with
990 Hz
1010 Hz
900 Hz
1100 Hz
1200 Hz
1300 Hz
800 Hz
700 Hz
980 Hz
1020 Hz
950 Hz
1050 Hz
13
How are sounds resolved?
14
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.