Physiology of the Ear HUMAN EAR SOUND WAVES LOUNDNESS PERCEPTION MEASURING LOUNDNESS CHARACTERISTICS OF SOUND IN SPEEACH AND MUSIC

1. ARCHITECTURAL
ACOUSTICS

2. HUMAN EAR
• The human ear is an organ of marvelous sensitivity,
complexity, and robustness.
• For a person with acute hearing, the range of audible sound
spans ten octaves, from 20 Hz to 20,000 Hz.
• The wavelengths corresponding to these frequencies vary
from 1.7 centimeters (5/8 inch) to 17 meters (57 feet), a
ratio of one thousand.
Physiology of the Ear

3. • The quietest sound audible to
the average human ear, about
zero dB at 1000 Hz,
corresponds to an acoustic
pressure of 20 × 10−6 N/m2
or Pa.
• Since atmospheric pressure is
about 101,000 Pa (14.7 lb/sq
in), it is clear that the ear is
responding to extraordinarily
small changes in pressure.

4. • The anatomy of the ear is organized into three parts,
termed outer , middle, and inner.
• The outer part includes the pinna, the fleshy flap of
skin that we normally think of as the ear, and a tube
known as the meatus or auditory canal that conducts
sound waves to the tympanic membrane or ear drum,
separating the outer and middle ear sections.
• The pinna gathers the sound signals and assists in
the localization of the height of a sound source.

5. • HUMAN EAR

7. SOUND WAVES

8. • The 2.7 centimeter (one-inch) long auditory canal acts
like a broadband quarter-wavelength tube resonator,
whose lowest natural frequency is about 2700 Hz.
• This helps determine the range of frequencies where the
ear is most sensitive—a more or less 3 kHz wide peak
centered at about 3400 Hz.
• The auditory canal resonance increases the sound level
at the ear drum around this frequency by about 10 dB
above the level at the canal entrance

9. LOUNDNESS PERCEPTION
Loudness is the human perception of the magnitude of a
sound.
• The perception of loudness is related to sound pressure
level, frequency content and duration of sound.
• The human auditory system averages the effect of SPL
over a 600-1000 ms interval.
• A sound of constant SPL will be perceived increase in
loudness as samples of duration 20,50,100,200 ms are
heard ,up to duration of about 1 second at which point the
perception of loudness will stabilize.

10. MEASURING LOUNDNESS
• Loudness can be measured in terms of intensity.
• Intensity – sound energy transmitted per second
through a unit area in a sound field.
• We can hear a large range of intensities (ratio of: 1 000
000 000 000 / 1; level of 120 dB above the faintest
sound)
• A logarithmic scale that expresses the ratio of two
intensities - decibel sound intensity (pressure) level (dB
SIL, dB SPL)
• dB SPL = 10 log10(I1/I0) = 20 log10(P1/P0)

12. • Note that the scale on the x-axis is in decibels (db) and recall
that 20 dB is a factor of 10, so a rock band (120 dB) is 100,000
times greater in amplitude than rustling leaves (20 dB).
• Loudness, like pitch, is a perceptual (not a physical) quantity.
• When we measure the range in terms of psychological units
(the Tones scale, established by Stevens and others via
magnitude estimation), we find a rock band sounds about
1000 times louder than rustling leaves.

13. CHARACTERISTICS OF SOUND IN SPEEACH AND
MUSIC
• A sound is any vibration
(wave) travelling through
the air or other Medium
which can be heard when
it reaches a persons ear.
Sound waves are:-
• Longitudinal- oscillations parallel to
propagation
• Mechanical-require a medium to
travel through
WHAT IS SOUND ?

14. SPEECH
 The speech signal is a slowly time varying signal in
the sense that, when examined
 over a sufficiently short period of time “between 5
and l00 m sec,”.
 its characteristics are fairly stationary; however,
over long periods of time (on the order of 1/5
seconds or more), the signal characteristics change
to reflect the different speech sounds being spoken.

15. CHARACTERISTICS OF SPEECH
Any audible sound has three important characteristics
 1.pitch
 2.loundness
 3.timbre
PITCH:
 Related to frequency of sound
Loudness:-
 Related to intensity of sound.
Timbre:-
 Related to Quality of sound.

16. Audible range :-
about 20HZ to 20,000HZ: upper limited with age
ULTRASOUND :-
Above 20,000HZ see ultrasonic camera focusing below
Infrasound:-
Below 20 HZ

17.  Frequency or Pitch: It is the number of cycle or pressure vibrations
produced by a body in unit of time.
 The greater the number of cycles or vibrations, the higher will be the
pitch.
 The grater the frequency higher the pitch and the lesser the frequency
the lower the pitch
 .
 Frequency of sound is the measure of the quality of sound. Frequency of
sound can be measured in cycles per second or hertz (Hz).
 A healthy young person is capable for hearing sound energy from about
20 to 20000 Hz.

18. Loudness or Intensity: It is the flow of wave energy crossing
per unit time through unit area.
• Sound intensities are measured in decibels (dB).
• For example, the intensity at the threshold of hearing is 0 dB, the
intensity of whispering is typically about 10 dB.
• Sound intensities are arranged on a logarithmic scale due to a wide range
of variations of the intensity of sound.
• Intensity of sound can be calculated by the following equation;
I =
Where I = sound intensity (w/m2
W = sound power (Watt)
d = distance form sound source (m)

19. Quality or timber: It is the quality of musical note.
• It is one of the important characters of the sound that allows the ear to
differentiate between tones produced by different instruments when the
sound waves are identical in aptitude and frequency.
• Example if a person played a violin, second person played piano and third
person a tuning fork, all at the same volume, the tones are identical in
frequency and amplitude, but different in quality.
• From these three sources, the simplest tone is
• produced by the tuning fork; the sound

20. • Amplitude or Volume: Amplitude is the characteristic of sound
waves that humans perceive as volume.
• The amplitude corresponds to the distance that air molecules move
back and forth as a sound wave passes through them.
• As the amount of motion in the molecules is increased, they strike the
ear drum with progressively greater force.
• This causes the ear to perceive a louder sound.
• This comparison of samples at low, medium, and high amplitudes
demonstrates the change in sound caused by altering amplitude.
• These three waves have the same frequency, and so should sound the
same except for a perceptible volume difference.

21. CHARACTERSTICS
SOUND IN SPEECH
• Typical outputs for normal
intensity speech can range
from 53 dB SPL for the [th] as
in 'think' to about 77 dB SPL
for the [a] in 'father'.
• Shouted speech can reach 83
dB SPL. This 24 dB range (+/-
12 dB) is related to the
characteristics of the human
vocal tract and vocal chords.

22. • A typical example of speech signal is which shows the
time waveform corresponding to the sounds in the phrase
". . . very good night . . ." as spoken by a male speaker.
AMPLITUDE
2SEC
P h a se (ra d ia n s)
A
B 22HZ

23.  A typical example of speech signal of speaking the two-second long
phrase “very good night”: (a)
 Time domain (b) Spectrum, and (c) Phase.
 is a typical example of music portion; it is clear from the spectrum that it
 is possible to distinguish if the spectrum is originally speech or music.
AMPLITUDE
A
B
2 seconds
22Hz

24. SOUND IN SPEECH WAVES

25. MUSIC
 Music can be on the order of
100 dB SPL with peaks and
valleys in the spectrum of +/-
18 dB.
 In fact, peaks for a 100 dB SPL
musical input can cause
conventional hearing aid
microphones to distort (since
the maximum transduction
capability is 115 dB SPL).

26. CHARACTERSTICS OF SOUND IN MUSIC
• The basic characteristics of sound and the fundamentals of music are by
their very nature a necessary tools to use in many of the future papers I
will be presenting over time.
• The basic characteristics of sound consist of only four fundamentals;
PITCH
DURATION
QUALITY
INTENSITY
• The character of the sequence of sounds and its arrangement is what
makes music subjectively pleasing and individually enjoyed.

27. PITCH
• Pitch perception in music is often
thought of in two dimensions, pitch
height and pitch chroma (Shepard,
1964). (asatrk 52)
• This is to account for the perceived
similarity of pitches that are separated by
octaves.
•
• Pitch height is the low / high dimension
of pitch.
• The relative position of a pitch within a
given octave is referred to as its chroma.

28. DURATION
Duration is the second basic characteristics of sound
• In music, the duration is determined by the moment the
tone becomes audible until the moment the sound falls
outside of our ability to hear it or it simply stops.
• In music notation, a half note is longer than an eighth
note, a quarter note is shorter in duration than a
whole note, for example

29. QUALITY
• Quality is our third basic characteristic of sound

30. INTENSITY
• It is a measure of the loudness of the tone. Assuming that
the pitch, duration and tonal qualities are the same, we
compare two or more tones based upon loudness or
intensity.
• the four basic characteristics of sound; pitch, duration,
quality and intensity collectively can be observed in all
sounds from any source including those made by musical
instruments.

31. AMPLITUDE
The frequency spectrum and the evolutionary spectrum of the average of
500 different speech and music specimens

32. A WEIGHTED SOUND LEVELS
 History of A-weighting
 A-weighting began with work by Fletcher and Munson
 which resulted in their publication, in 1933, of a set of equal-
loudness contours.
 Three years later these curves were used in the first American
standard for sound level meters
 This ANSI standard, later revised as ANSI S1.4-1981,
incorporated B-weighting as well as the A-weighting curve,
recognising the unsuitability of the latter for anything other than
low-level measurements.

33. A WEIGHTED SOUND LEVELS
• It has been known for a long time that the frequency
response of human hearing is anything but linear.
• To improve on acoustic measurements, weighting curves
were created to compensate for sound at different levels.
• A-weighting is applied to instrument –measured sound
levels in an effort to account for the relative loudness
perceived by the human ear As the ear is less sensitive to
low audio frequencies.
• A-weighted though originally intendad only for the
measurement of low-level sounds.

34. • The A-weighting curve was created to compensate
for sound along the 40 Phon contour.
• Its commonly used for the measurement of
environmental noise and industrial noise as well
as when assessing potential hearing damage
and other noise health effects.

36. • The A-weighting system is used in any measurement of
environmental noise (examples of which include roadway
noise, rail noise, aircraft noise).
• A-weighting is also in common use for assessing potential
hearing damage caused by loud noise.
• The A-weighting is also used for noise dose
measurements at work.
• A noise level of more than 85 dB(A) each day increases
the risk factor for hearing damage.
A-WEIGHTED SOUND MESURING

37. • A-weighted decibels are abbreviated dB(A) or dBA.
When acoustic (calibrated microphone) measurements
are being referred to, then the units used will be dB SPL
referenced to 20 micropascal = 0 dB SPL. dBrn
adjusted is a synonym for dBA
• The A-weighting curve has been widely adopted for
environmental noise ,measurement, and is standard in
many sound level meters.