Structure of the Ear

Structure of the Ear

• Structure of the Ear

• Perception of Loudness (Energy)

• Perception of Pitch (Frequency)

• References

Psychoacoustics

• Psychoacoustics

• is the study of

• subjective human perception

• of sounds.

The length of the auditory canal has been greatly exaggerated

• The length of the auditory canal has been greatly exaggerated

Auditory canal is a resonator at approximately 2000 to 5000 Hertz.

• Auditory canal is a resonator at approximately 2000 to 5000 Hertz.

The bones (ossicles) of the middle ear form a lever which “amplifies” the displacement by a factor of 3x.

• 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

Reference: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/place.html#c1

• Reference: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/place.html#c1

Fechner’s law and decibel scale

• Fechner’s law and decibel scale

• Discrimination (jnd)

• Threshold of hearing

Reference: http://www.phys.unsw.edu.au/jw/dB.html

• Reference: http://www.phys.unsw.edu.au/jw/dB.html

1860 Fechner’s Law

• 1860 Fechner’s Law

• As stimuli are increased by multiplication, sensations increase by addition (Sensation grows as the logarithm of the stimulus)

• Example: A 10x bigger intensity sound is “heard” as only 2x bigger by the ear

The decibel is a logarithmic scale

• The decibel is a logarithmic scale

• A multiplicative factor of 10x in intensity is +10 db

• 0 db is threshold of hearing

• 1 db is just noticeable difference

• 15 db is a whisper

• 60 db is talking

• 120 db is maximum safe level

• 150 db is jet engine (ear damage)

• 180 db stun grenade

Reference: http://www.phys.unsw.edu.au/jw/dB.html

• Reference: http://www.phys.unsw.edu.au/jw/dB.html

jnd = “just noticeable difference”

• 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

Reference: http://www.phys.unsw.edu.au/jw/dB.html

• Reference: http://www.phys.unsw.edu.au/jw/dB.html

Note “Sound Pressure dB” (or SPLdB) is approximately half regular “energy” decibels (dB).

• Note “Sound Pressure dB” (or SPLdB) is approximately half regular “energy” decibels (dB).

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 )

• 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 the square of the pressure amplitude Minimum ear can hear is 0.000,02 Pascals (Atmospheric pressure is 100,000 Pascal)

3c Phon & Equal Loudness Level

• The Fletcher-Munson curves are a way of mapping the dB of a pure tone to the perceived loudness level in phons.

3d 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

Range of Hearing

• Range of Hearing

• Pitch Discrimination and jnd

• Combination tones

Humans can hear from 16 to 20,000 Hertz

• 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

High Frequency Test

• High Frequency Test

• http://audiocheck.net/audiotests_frequencycheckhigh.php

• Low Frequency Test

• http://audiocheck.net/audiotests_frequencychecklow.php

At 1000 Hz, the “jnd” is about 1 Hz (0.1%)

• 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

Two tones closer than 15 Hertz we hear as a “fused” tone (average of frequencies) with a “beat”.

• Two tones closer than 15 Hertz we hear as a “fused” tone (average of frequencies) with a “beat”.

When tones are far enough apart we hear them as two distinct tones

• When tones are far enough apart we hear them as two distinct tones

• We also hear difference and sum tones that are not really there (Tartini Tones 1714)

http://en.wikipedia.org/wiki/Weber-Fechner_law

• http://en.wikipedia.org/wiki/Weber-Fechner_law

• 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

Excluded SONE scale of hearing

• Excluded SONE scale of hearing