Transcript Kein Folientitel

Physiological and Physical
Principles
of the Human Hearing
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The Human Ear
Pinna
Ossicles:
Malleus
Incus
Stapes
Labyrinth
Acoustical
Nerve
Oval
Window
Cochlea
Ear
drum
Middle
Ear
Oval
Window
Outer Ear
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Middle Ear
Eustacian
Tube
Inner Ear
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Middle Ear
Capabilities
1) ImpedanceMatching between the
sound impedance of air (400 kg*m-2*s1) and the vibration impedance of the
inner ear.
(The impedance of water 3600 times
higher: 1 480 000 kg*m-2*s-1)
The impedance transformation is 1: 20
2) Protection from high sound levels:
The acoustical reflex.
The ossicles reduce the sound level by
6 –10 dB. This is known as temporaray
hearing attenuation ofter hearing loud
sounds.
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Outer Ear
Capabilities
Enables localisation in the meredian plane:
Front, Back Above
The localization depends on the spectrum of the
sound:
If other clues are missing, subjects will localize
a frequency shaped noise as shown on the
right:
Maximum at 1 kHz: Back
Maximum at 300 Hz and 3 kHz: Front
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Design of the Inner Ear
Cut through
Cochlea
Inner Hair Cells
3 Rows of Outer
Hair Cells
Basilar
Membran with inner and
outer hair cells
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Hair cells in an
electron microscope
5
Mechanical Model of the Inner Ear
Mechanical model of the Cochlea:
Travelling waves in a box with a membrane of variable mass and stiffness
High frequencies have their maximum
at the beginning, low frequencies at
the end of the cochlea.
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Inner Ear: Frequency Selectivity and Sensitivity
The frequency selectivity and sensitivity of the human ear is several magnitudes better
than expected from the mechanical model:
At the hearing threshold the displacement of the basilar membrane is the size of a
hydrogen atom only!
Theory: The 90.000 outer hair cells are part of an active feedback amplification system.
Hearing Impaired
Author
(Age 29)
Neural Tuning Curve: Activity in the
hearing nerve of a cat as response
on tones of different level and
frequency.
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Psychoacoustical Tuning Curve with
hearing and discomfort level of the
author and of a hearing impaired
person
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Combination of Tones
Modulation
Two tones with a frequency distance of up to
15 Hz:
Perception of modulation.
Maximum is perceived at about 5 Hz:
Modulation frequency of syllables
A
f
Harshness
Two frequencies having a frequency distance
of 30-150 Hz: Perception of harshness.
Maximum is perceived at 80-120 Hz
A
f
Two Tones
Two frequencies having a frequency distance
of more than 150 Hz: Perception of two
distinct tones.
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f
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The Ear: Technical Data
Sensitivity: Hearing Level at 20 Pa corresponding to 10-16 W/cm2 . The
displacement of the basilar membran is the size of a hydrogen atom only!
Dynamic Range: 6 magnitudes, corresponding to 120 dB.
Frequency Channels: 30.000 inner hear cells with filter slopes of 180dB/Oktave.
Frequency Resolution: 3 Hz change at 1 kHz perceivable.
Amplitude resolution: Logarithmic, 1 dB change is perceivable
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Block Diagram of the Neural Processing
Simplified diagram of the auditory
path for one cochlea (lower right).
The top level shown is the primary
acoustical cortex.
Several connections between left
and right brain regions are
indicating significant binaural
processing capabilities.
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Hearing Level, Curves of Equal Loudness
• At low and high frequencies the hearing threshold rises. Otherwise we would hear our
own blood flow.
• Curves of equal loudness are modeled by A-, B- and C-compensation curves
• At 120 dB, or 6 magnitudes beyond the hearing threshold is the pain threshold
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Frequency Groups
A 2 kHz tone is presented in 10 falling amplitude steps of 5 dB.
The tone is then masked with wide-band noise noise and noise with bandwith of 1000, 250 and 10
Hz.
The spectral level of the noise is constant. When the bandwith is reduced the perceived loudness
drops significantly. But only when the noise bandwith is smaller than a frequency group we can
perceive more steps of the tone.
Amplitude
Frequency
group bandwith
Frequency
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wide-band noise
Noise 1kHz
bandwith
noise
250 Hz
band
with
noise
10 Hz
bandwith
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The dB Scale
The logarithmic loudness perception with
wide band noise
10 steps with 6 dB attenuation (60 dB dynamic range)
15 steps with 3 dB attenuation (45 dB dynamic range)
20 steps with 1 dB attenuation. The smallest perceivable
loudness change is 1 dB.
Tracks 8-10
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Virtual Pitch
On the phone (300 Hz to 3kHz) the fundamental of a speaker is not transmitted. We still can tell
male and female speakers apart.
A tone comples of 10 harmonics with a base frequency of 200 Hz generates the pitch sensation
of the fundamental.
Perceived pitch
Frequency
Initially the fundamental, then more and more harmonics are taken away. The pitch sensation
changes only when just a few components are left over.
Empfundene Tonhöhe
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Frequenz
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Virtual Pitch: Shepard‘s Paradox
Ten octave tones are incremented in frequency. A weighting function allows to
add new low tones without catching the attention.
The effect is an ever increasing pitch.
The second example demonstrates a decreasing pitch.
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Literature
1. SCHROEDER, M.R. Models of Hearing. Proc. IEEE, Vol63, No. 9, September 1975
2. MEYER, E., Neumann, E.G. Physikalische und Technische Akustik. ISBN 3 528 1 8255 5, Vieweg, 1974
3. ZWICKER, E. Schallrezeption am Beispiel höherer Säugetiere und des Menschen
3. ENGSTRÖM, H., ENGSTRÖM, B. Structure of the hairs on cochlear sensory cells. Hearing Research, 1 (1978)
Elsevier/North-Holland Biomedical Press
4. LEWIEN, T. Filterung von Spracheinhüllenden zur Verständlichkeitsverbesserung bei Innenohrschwerhörigkeit.
Dissertaton Göttingen, 1983.
5. KAY, R.H. Hearing of Modulation in Sounds. Physiological Revievs Vol. 62, No.3, USA, 1982.
6. SCHREINER, C., CYNADER, M. Basic Functional Organisation of Second Auditory Cortical Field (AII) of the Cat.
Journal of neurophysiology, Vol. 51, No. 6, June 1984
7. ZWICKER,E., Fastel,H. Psychoacoustics. Springer 1990. ISBN 3-540-52600-5
8. KOLLMEIER, B. Script zur Vorlesung über physikalische, technische und medizinische Akustik. Oldenburg, 1999
9. HOUTSMA et al. Auditory Demonstrations. CD. Mit Heft. IPO, Philips, No. 1126-061, 1987.
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