This document discusses the physics of sound and how humans perceive attributes like loudness. It covers topics like sound pressure level, the inverse relationship between intensity and distance, and how loudness depends on factors like frequency, bandwidth, duration, and partial masking. Loudness is measured in phones and contours of equal loudness show how loudness level varies with frequency. The ear's loudness response depends on critical bands and loudness can be greater for binaural vs monaural sounds. Intensity discrimination involves changes in neuron firing rates and patterns at different sound levels.
Diurnal Variability of Underwater Acoustic Noise Characteristics in Shallow W...TELKOMNIKA JOURNAL
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(pdf). The results show the UWAN has a non-Gaussian pdf and is colored. Moreover, the difference in
UWAN characteristics between day and night is studied and the noise power at night is found to be more
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Describes wave motion in general and specifically sound waves
**More good stuff available at:
www.wsautter.com
and
http://www.youtube.com/results?search_query=wnsautter&aq=f
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1. MUSICAL ACOUSTICS
SOUND
PRESSURE,
POWER AND
LOUDNESS
Science of Sound
Chapter 6
2.
3.
4. FREE FIELD
I = W/4πr2
at r = 1 m:
LI = 10 log I/10-12
= 10 log W/10-12 – 10 log 4p
= LW - 11
5. HEMISPHERICAL
FIELD
I = W/2pr2
at r = l m
LI = LW - 8
Note that the intensity I α 1/r2 for both free and
hemispherical fields;
therefore, LI decreases 6 dB for each doubling of distance
6. SOUND PRESSURE LEVEL
Our ears respond to extremely small pressure
fluctuations p
Intensity of a sound wave is proportional to the sound
Pressure squared:
ρc ≈ 400
I = p2 /ρc ρ = density (1.21kg/m3)
c = speed of sound (343 m/s)
We define sound pressure level:
Lp = 20 log p/p0 p0 = 2 x 10-5 Pa (or N/m2)
(or SPL)
9. MULTIPLE SOURCES
What we really want to add are mean-square
average pressures (average values of p2)
This is equivalent to adding intensities
Example: 3 sources of 50 dB each
Lp = 10 log [(P12+P22+P32)/P02] = 10 log (I1 + I2 + I3)/ I0)
= 10 log I1/I0 + 10 log 3 = 50 + 4.8 = 54.8 dB
10. SOUND PRESSURE and INTENSITY
Sound pressure level is measured with a sound level meter (SLM)
Sound intensity level is more difficult to measure, and it requires
more than one microphone
In a free field, however, LI ≈ LP
11. FOUR ATTRIBUTES USED TO DESCRIBE A SOUND:
•Loudness
•Pitch
•Timbre
•Duration
EACH OF THESE DEPENDS ON ONE OR MORE PHYSICAL
PARAMETERS THAT CAN BE MEASURED:
•Sound pressure
•Frequency
•Spectrum
•Duration (measured)
•Envelope
Relating the SUBJECTIVE QUALITIES to the PHYSICAL
PARAMETERS that we can MEASURE OBJECTIVELY
Is an important problem in PSYCHOACOUSTICS
29. LOUDNESS RECRUITMENT
UNUSUALLY RAPID GROWTH OF LOUDNESS
ABOVE A CERTAIN THRESHOLD
GENERALLY ASSOCIATED WITH HEARING LOSS,
BUT NORMAL LISTENERS EXPERIENCE IT FOR
TONES OF VERY HIGH OR VERY LOW FREQUENCY
30. MONAURAL vs BINAURAL LOUDNESS
FOR SOFT SOUNDS (~20dB) BINAURAL
LOUDNESS EXCEEDS MONAURAL LOUDNESS
BY A FACTOR OF 2
(CORRESPONDS TO ΔL = 8dB)
FOR LOUD SOUNDS (~80dB) BINAURAL
LOUDNESS EXCEEDS MONAURAL
LOUDNESS BY A FACTOR ~/.4
(CORRESPONDS TO ΔL = 6dB)
Zwicker & Fastl (1990)
31. INTENSITY DISCRIMINATION AND CODING
AT LOW LEVELS, INTENSITY CHANGES CAN BE
SIGNALLED BOTH BY CHANGES IN FIRING RATES OF
NEURONS AT THE CENTER OF THE EXCITATION
PATTERN AND BY THE SPREADING OF THE EXCITATION
PATTERN (TO INCLUDE MORE NEURONS)
AT HIGH LEVELS, MOST NEURONS AT THE CENTER OF
THE EXCITATION PATTERN ARE SATURATED, BUT
INTENSITY CHANGES ARE SIGNALLED BY CHANGES
IN FIRING RATES AT THE EDGES.
AN INCREASE IN LEVEL ALSO MAY BE SIGNALLED
BY INCREASED PHASE LOCKING TO THE TONE WHICH
RESULTS IN TEMPORAL REGULARITY OF
NEURAL FIRINGS
