Psychoacoustics

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Psychoacoustics

• Olga Umnova
• o.umnova_at_salford.ac.uk

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What is the subject of psychoacoustics?
Systems relevant to the sounds we hear
Instrument air listener (source) -
(medium) (receiver)
We will be interested in how sounds are
perceived, what sensations they cause and why.
The most interesting for us is listener and his
sensations.
Psychoacoustics is the study that links acoustic
stimuli with the auditory sensations (JG Roederer)
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Pure tone sine wave
What parameters are used to describe pure tones
in physical acoustics?
Amplitude A (measured in Pa) You can also
measure it in dB! You can use Intensity instead
of amplitude (remember how they are
related?) Frequency f (measured in Hz) Phase
(waves on the graph have different phase)

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Complex tone any periodic wave can be
represented as a sum of sine waves having
appropriate amplitude, frequency and phase. They
all are harmonics of a single frequencies (f, 2f,
3f) (Fourier analysis)
Simple example of complex tone and its spectrum
signal
signal
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2
4
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time
frequency
What parameters are used to describe complex
sounds in physical acoustics?
Spectral composition (which harmonics are
present) additional descriptor needed
for complex tone
Amplitude and phase of each harmonic
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Subjective attributes of sound
What are the factors that distinguish one single
tone from any other in musical performance? What
subjective descriptors we use to characterise
musical sound? How are they related to the
measurable properties of the corresponding
vibrations?
Pitch is a measure of highness or lowness
of sound Loudness Timbre (or tone quality)
Localization
And many others!
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More about pitch
Pitch and intensity. Can we change pitch by
changing signal intensity?
Demonstration 2 In the demonstrations tones with
frequencies 200, 500, 1000, 3000 and 4000 Hz are
presented in pairs with the second tone in pair
having a level 30dB higher than the first one.
Can you sense pitch difference? Which tone has
higher pitch at each frequency?
A high pitch (gt2kHz) will be perceived to be
getting higher if its loudness is increased,
whereas a low pitch (lt2kHz) will be perceived to
be going lower with increased loudness.
However it cannot be perceived accurately above
5 kHz.
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More about loudness
Loudness is not simply sound intensity!
Demonstration 1
In the demonstration we hear broadband noise
reduced in steps of 1dB. This means that
intensity of the last signal is 100 times lower
than that of the first signal. Did loudness
decrease was that much?
A general "rule of thumb" for loudness is that
the intensity must be increased by about a
factor of ten to sound twice as loud.
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More about timbre
Timbre mainly depends of spectral composition
Official definition of timbre Timbre is that
attribute of auditory sensation in terms of which
a listener can judge two sounds similarly
presented and having the same loudness and pitch
as being dissimilar (ANSI, 1960) We can not
measure timbre using our subjective scale (can
not say that it is high or low). Strange
associations are used sometimes to describe
timbre warm, rich, open, dull, colourless
Effect of spectrum on timbre Demonstration
1 You will hear how how the sounds of two
instruments are synthesized by adding harmonics
to the fundamental. Can you recognize the
instruments?
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Localization another subjective characteristic
of sound
We can sense direction of the sound source
because we have 2 ears! For sound with
frequencies below 1kHz we can sense a slight
phase difference between sounds Arriving in our
ears, i.e. peaks of the sound pressure will
arrive at one ear slightly after they arrive at
the other.
Our auditory system detects and interprets this
phase difference.
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Not all subjective characteristics of sound can
be easily related to physical parameters!
CONSONANCE and DISSONANCE are subjective feelings
associated with 2 (or more) simultaneously
sounding tones. Tones with particular frequency
relations f2/f1 sound pleasing for our ears
(consonance). It seems to indicate that the
human auditory system possesses a sense for
certain special frequency intervals unison
(f2/f11), an octave (f2/f12), fifth
(f2/f13/2), fourth (f2/f14/3), major third
(f2/f15/4)
The white keys of the piano give the seven notes
of the C-major diatonic scale
Listen to C-E (major third)
Listen to C-D
Did you find the first combination a little more
pleasant?
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Physical acoustics and psychoacoustics
similarities and differences
Acoustics
Psychoacoustics
Make predictions on the response of the specific
system subjected to given boundary conditions
Similar. System- subjects auditory
system, boundary conditions- determined by
auditory stimuli, response auditory sensations
Aim
Methods
Models (simplifications of real systems) and
experiments
Similar.
Results
Exact, do not depend on the measuring methods
Different. Results are never exact. Only
probabilities, i.e. likelihood, can be predicted.
Statistical interpretation of the results is
always required
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Approximate schedule

• Lecture 1 Introduction into subject of
  psychoacoustics
• Lectures 2-3 Physiology of hearing
• Lectures 4-5 Perception of pure tones
• Lectures 6-7 Perception of two (or more) pure
  tones

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Approximate schedule (contd)

• Lecture 8 Perception of (single) complex tone
• Lectures 9 Perception of superimposed complex
  tones dissonance and consonance
• Lecture 10 Perception of loudness
• Lecture 11 Masking
• Lecture 12 Perception of space

Please note module specification in the Student
Handbook slightly outdated
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Homework assignments (2 in total)
Assignment 1 (due end of Week before Easter)
Physiology of hearing and pure tone
perception Assignment 3 (due end of Week 11)
Perception of complex tones. Perception of
Loudness. Masking.
They account for 25 of the total mark
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Recommended reading

• JG Roeder The Physics and Psychophysics of
  Music, Springer Verlag, 1995
• BCT Moore An Introduction to the Psychology of
  Hearing, Academic Press, 1997
• JR Pierce The Science of Musical Sound, WH
  Freeman, 1992
• AH Benade Fundamentals of Musical Acoustics,
  Dover 1991
• DM Howard and JAS Angus Acoustics and
  Psychoacoustics Focal Press 2001