This document discusses the characterization of sound through a review of key concepts. It defines sound physically as a wave motion and psychophysically as the excitation of hearing. Sound is transmitted through a medium and produced by a vibrating object contacting air. The attributes of sound - loudness, pitch, timbre and duration - have both subjective and objective physical definitions related to parameters like pressure, frequency and spectrum. The relationships between these physical parameters and perceptual qualities are explained, along with concepts like octaves and consonance/dissonance.

1. Characterization of sound – a review
R.Narasimha Swamy
Senior consultant
narasimhaswamy@yahoo.com

2. What is sound?
 Sound can be defined in two ways. [Physical or psychophysical]
 Sound can be defined as a wave motion in air or other elastic
media.
 Or as excitation of the hearing mechanism that results in the
perception of sound [sensation].

3. Transmission of Sound
• Requires a medium with elasticity and
inertia (air, water, steel, etc.)
• Movements of air molecules result in the
variation of sound pressure causing the
propagation of a sound wave

4. How sound is produced?
 Energy in the form of sound is produced when a
vibrating surface or object is contact with the air.
 Sources of sound
Vocal
Plucked strings
Air column
Vibrating plate

5. How sound is perceived?
 Physical stimulation of the ear by the sound wave.
 Physiological and psychological processing and
perception in ear and brain (psycho-acoustics)
resulting from nerve impulses stimulating the
acoustic cortex of the brain.

6. Attributes of the sound
• Loudness, pitch, timbre and duration are
subjective qualities used to describe a particular
sound stimuli.
• Each of these attributes depends on one or more
physical parameters viz Sound pressure,
frequency, spectrum, duration and envelope that
can be physically described and measured.

7. Amplitude
• Normally, sound is measured in terms of sound pressure level (SPL).

8. • Amplitude and frequency

9. Relation between power, intensity and pressure

10. Power, intensity and pressure

11. • Acoustical energy emitted by the sound
source
• Unaffected by the environment
• Expressed in terms of watts (W) with
reference as 10-12 Watts
Sound Power and Sound Pressure – an analogy
• Pressure disturbance in the atmosphere
• Expressed in terms of Pascal (Pa) that can
be measured directly. Ref level is 2x10-5Pa
• What our ears hear and what sound meters
measure
• Affected by strength of source, surroundings,
and distance between source and receiver
• Affected by strength of source, surroundings,
and distance between source and receiver

12. SOUND PRESSURE LEVEL
 Our ears are sensitive to extremely small pressure
fluctuations, p
 Intensity I of a sound wave is proportional to the sound
Pressure squared
 I = p2 /ρc
Where ρ = density
c = speed of sound
ρc ≈ 400
 We define sound pressure level:
 Lp = 20 log p/p0.
 p0 = 2 x 10-5 Pa (or N/m2) (or SPL)

14. Magnitude (SPL) of typical sounds
Weakest perceivable sound heard 0dB
Whisper in a quiet Library, Studio 30dB
Normal conversation (3-5') 60-70dB
Telephone dial tone 80dB
City Traffic (inside car) 85dB
Train whistle at 500', Truck Traffic 90dB
Subway train at 200' 95dB
Level at which sustained exposure may result in hearing loss 90 - 95dB
Motorcycle 100dB
Sandblasting, Loud Rock Concert 115dB
Pain begins 125dB
Pneumatic riveter at 4' 125dB
Even short term exposure can cause permanent damage - Loudest recommended
exposure WITH hearing protection 140dB
Jet engine at 100', Gun Blast 140dB
Death of hearing tissue 180dB
Loudest sound possible 194dB
• For ease of convenience, sound pressure level (SPL) is used.
• SPL is measured in decibel scale (db) - a ratio scale.

15. Loudness
• Perceived loudness is the intensity attribute of the
sound.
• Loudness relates to the dynamics of the music.
• Loudness does not have simple one to one relation
with the magnitude/SPL.
• Loudness is also the function of frequency, duration
etc.
• At 1 kHz, at low levels, a 3 dB change is the least
detectable by the ear, but at high levels, the ear can
detect 0.25 dB change.

16. Fletcher Munson equi loudness contours

17. Frequency
• Human beings (adult, healthy) can hear frequencies in the
range of 20 Hz to 20,000 Hz.
• Spoken words have frequency band of 170 Hz to 4000 Hz.
• Natural musical instruments have frequency band of 50 Hz
to 8500 Hz.
• Though pitch and frequency are not same, they are
correlated.

21. Pitch
• Pitch: A subjective term for the perceived frequency
attribute of a tone.
• One key distinction between these terms is that, pitch is
relative (a matter of common agreement among
musicians), while frequency is absolute (a precise,
unambiguous measurement).
• Frequency describes a physical phenomenon, while
pitch describes a perceptual phenomenon.

22. Attributes Pitched Non pitched
Example Musical note Noise
Waveform
[Time
domain]
Periodic Non-periodic
Spectrum
[Frequency
domain]
Lines Continuous
Pitch

23. Dependence of loudness on SPL and frequency
 A range of frequencies which are perceived by the ear as the same pitch
and out same loudness level.
 All frequencies in a critical band activate the same area on the basilar
membrane.

24. Duration
• The duration (time length) of a particular note is defined
by how long it lasts compared to a whole note.
• Duration is a property of tone that becomes one of the
bases for rhythm.

25. Timbre, the color of the music
• Timbre describes all of the aspects of a musical sound that do
not have anything to do with the sound's pitch, loudness or
length.
• In other words, if a flute plays a note, and then a violin plays
the same note, for the same length of time, at the same
loudness, we can still easily distinguish between the two
sounds.
• This difference is in the timbre of the sounds. This is due to
the variation in the spectral characteristics of the sound.

26. Analyzing non sinusioidal wave
• If the wave pattern is periodic i.e repetitive, it can
be represented as combination of different
sinusoidal waves.
• This is based on a mathematical technique known
as Fourier series.

27. Adding fundamental and harmonic result
in complex wave

28. Tone
Time domain
Frequency domain

29. Time domain
Frequency domain

30. Time domain
Frequency domain

31. Wave shape and spectra of
A4 (440 Hz) pitch on different instruments
Time domain Frequency domain

32. Dependency of subjective qualities of sound
on physical parameters
Physical
parameter
Subjective quality
Loudness Pitch Timbre Duration
Pressure +++ + + +
Frequency + +++ ++ +
Spectrum + + +++ +
Duration + + + +++
Envelope + + ++ +

33. Summary
 There is a strong mathematical correlation between the
physical and perceived sound. It needs to be properly
studied, interpreted and understood.
 This knowledge is essential for interpreting the
measurement in planning and maintaining facilities for
sound recording and broadcasting.

34. Bibliography
1. Master hand book of acoustics by F.Alton Everest.
2. Animations by D.Russell.
3. Reading material from B&K
4. Indian Classical Music: Tuning and Ragas by Catherine
Schmidt-Jones

35. Questions?

36. Thank you

38. Musical note (swara)
• Note is a periodic sound wave of either single frequency
(tone) or of a particular shape.
• Discreatization of musical phenomena that, facilitate
performance, comprehension and analysis.

39. Octaves

40. Octaves
• The musical scale is based on octaves.
• Moving up one octave is defined as doubling the
frequency.
• The octave appears to be an important musical interval
in all musical cultures.
• To a human ear there is an obvious "sameness" about
the two notes played in different octaves.
• But why do they sound similar?

41. Consonance and dissonance
• Notes that sound good and melodious when
played together are called consonant.
• If it does not sound pleasing, it is called as
dissonance.
• The "simple frequency ratio" theory of
consonance is one of the oldest hypotheses in
musical thought.
• This phenomenon is due to the way ear processes
the sound by critical bands.