Lecture 10 - XXX#10 p 1 XXXXX#10 XXX p 2 XXXX#10 p 3 XXX...

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EEL 4930 Audio Engineering Lecture 10 Psychoacoustics (from http://en.wikipedia.org/wiki/Psychoacoustics ) Psychoacoustics is the study of subjective human perception of sounds . Alternatively it can be described as the study of the psychological correlates of the physical parameters of acoustics . Background Hearing is not a purely mechanical phenomenon of wave propagation, but is also a sensory and perceptual event. When a person hears something, that something arrives at the ear as a mechanical sound wave traveling through the air, but within the ear it is transformed into neural action potentials . These nerve pulses then travel to the brain where they are perceived. Hence, in many problems in acoustics , such as for audio processing , it is advantageous to take into account not just the mechanics of the environment, but also the fact that both the ear and the brain are involved in a person’s listening experience. The ear for example, takes a spectral decomposition of sound as part of the process of turning sound into neural stimulus, so certain time domain effects are inaudible. MP3 compression makes use of this fact. In addition the ear has a logarithmic dynamic response. Our telephone network makes use of this fact by logarithmically compressing data samples before transmission, and then exponentially expanding them for playback. Another side effect of the ear’s non-linear logarithmic response is that sounds which appear on the ear drum in close spectral proximity produce phantom beat notes. This is the same principle that is used for down conversion of carrier frequencies in radio front ends by a non-linear amplifier. Such physiological effects due to the ear’s anatomy are properly called physiology-acoustic effects, though people commonly lump them in with psycho-acoustic effects. There are true psycho-acoustic effects introduced by the brain. For example, when a person listens to crackly and needle-on-vinyl hiss-filled records, he or she soon stops noticing the background noise, and enjoys the music. A person who does this habitually appears to forget about the noise altogether, and may not be able to tell you after listening if there was noise present. This effect is called psycho-acoustical masking. The brain’s ability to perform such masking has been important for the adoption of a number of technologies; though in this age of digital signaling and high fidelity playback the effect is typically used to hide losses in compression rather than to cover up analog white noise . As another example of a psycho- acoustic effect, the brain appears to use a correlative process for pattern recognition; much like is done in electronic circuits that look for signal patterns. When the threshold for acceptance of a correlative match is very low a person may perceive hearing a sought after pattern in pure noise or among sounds that are somewhat indicative, as the brain fills in the rest of the pattern. This is a psycho-acoustic phantom effect.
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This note was uploaded on 02/08/2011 for the course EEL 4930 taught by Professor Staff during the Spring '08 term at University of Florida.

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Lecture 10 - XXX#10 p 1 XXXXX#10 XXX p 2 XXXX#10 p 3 XXX...

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