Lecture program Psychoacoustics and instrumentation

1. PSYCHOACOUSTICS
OF DISCRIMINATING AND
IDENTIFYING SOUNDS
Perceptual attributes of
acoustic waves

2. Effects of Duration on Loudness
■ The auditory system responds to abrupt intensity changes with a:
– "rise time" of ~200ms and a
– "decay time" of ~50ms.
■ The indicated "decay time" may explain why tones with frequency
above 20Hz (50ms period) are perceived as a single tone with
identifiable pitch rather than individual pulses or why amplitude
fluctuation rates above 20Hz may be perceived as "roughness" or
combination tones rather than as loudness fluctuations.

3. ■ In general, for durations up to ~200ms, (~400ms for broadband
noise) the longer the signal the louder it appears (i.e. the ear
averages sound energy over ~200ms for narrow band signals and
~400ms for broadband signals).
■ Within this duration range, tenfold increase in duration
corresponds to 10 Phons increase in loudness level.
■ For longer durations, no consistently reported loudness changes
have been recorded

4. ■ Loudness and time-delay among successively presented
stimuli:
– Presentation delay between signals also influences loudness,
but not in a significant way.
– You can deduce this influence from your understanding of
forward and backward masking.

5. Intensity discrimination & Just
Noticeable Difference (JND)
JND (just noticeable difference) for loudness: Approx. 1dB (for
pure tones, middle frequencies and 'regular' background noise)
Weber's law
According to Weber's (fraction) law, the smallest perceivable physical
change in a stimulus is proportional to the starting level of the
physical stimulus (called pedestal),

7. Adaptation, Fatigue
&
Temporary Threshold Shift (TTS)

8. Fatigue
As defined by Hood (1972)
Fatigue results from the application of a stimulus which is usually
considerably in excess of that required to sustain the normal
physiological response of the receptor, and it is measured after the
stimulus has been removed.
This is referred to Post-stimulatory auditory fatigue - Temporary
Threshold Shift (TTS)

9. Adaptation
Adaptation –The response of a receptor to a steady stimulus
declines as a function of time until it reaches a steady value at
which the energy expended by the receptor is just balanced by the
metabolic energy which is available to sustain it. –Appears as the
decline in apparent magnitude of the stimulus, followed by a
period where the magnitude remains constant.

10. Factors that affect TTS
■ Intensity of the fatiguing stimulus
■ Duration of the stimulus
■ Frequency of the stimulus
■ Frequency of the exposure to the stimulus
■ Time between the time where the stimulus is stopped and when
it is measured, usually referred to the recovery interval (RI)

11. A TTS lasting up to 16 hours to disappear is called a physiological
fatigue
A TTS lasting more than 16 hours to disappear is called a
pathological fatigue –Up to 3 weeks to recover

12. Psychoacoustics cannot be described at all without reference to the
man known as the "Einstein of the ear."
■ Through Dr. Tomatis research and findings, we have come to understand
the extraordinary power of the ear.
■ In addition to its critical functions of communication and balance, the
ear's primary purpose is to recycle sound and so recharge our inner
batteries.
■ According to Tomatis, the ear's first function in utero is to govern the
growth of the rest of the physical organism.
■ After birth, sound is to the nervous system what food is to our physical
bodies: Food provides nourishment at the cellular level of the organism,
and sound feeds us the electrical impulses that charge the neocortex.

13. In the realm of application-specific music and sound,
psychoacoustically-designed soundtracks revolve around the
following concepts and techniques:
■ Intentionality (focused application for specific benefit)
■ Resonance (tone)
■ Entrainment (rhythm)
■ Pattern Identification (active listening or passive hearing)
■ Sonic Neurotechnologies (highly specialized sound processing)