Lecture 3 c psychoacoustics of discriminating and identifying sounds
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This document discusses psychoacoustics and the perceptual attributes of sound. It covers several topics: 1) The effects of duration on loudness, including that sounds above 20Hz are perceived as a single tone rather than pulses, and amplitude fluctuations above 20Hz may be perceived as roughness rather than loudness fluctuations. 2) For durations up to 200ms, longer signals appear louder due to energy averaging over time. A tenfold increase in duration corresponds to a 10 Phon increase in loudness. 3) Adaptation, fatigue, and temporary threshold shifts from exposure to loud sounds over time. Factors like intensity, duration and frequency of exposure affect temporary threshold shifts. 4) Psychoac
Lecture 3 c psychoacoustics of discriminating and identifying sounds
- 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)