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chap 11 textbook notes

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Kristie Dukewich

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CH11 – Sound, the Auditory System and Pitch Perception  Pressure changes: complex tones The Sound Stimulus o COMPLEX TONES – waveform != a SINE WAVE, but a combination  SOUND – two definitions, physical & perceptual  is a PERIODIC TONE  the waveform repeats o PHYSICAL: sound is pressure changes in the air or other medium  Repetition rate of complex tone is called the o PERCEPTUAL: sound is the experience we have when we hear FUNDAMENTAL FREQUENCY of the tone  Sound as Pressure Changes  focus on sound from musical instruments o Sound stimulus occurs when an object’s movements/vibrations cause  Periodic complex tones consist of number of pure tones pressure changes in air, water, any elastic medium surrounding the o Can build a complex tone by ADDITIVE SYNTHESIS = number of sine- object –ex. loudspeaker vibrations affect surrounding air by: wave components are added together to create a complex tone  CONDENSATION – diaphragm moves out  push air molecules  FUNDAMENTAL FREQUENCY – starting point for creating a together, increase nearby molecule density complex tone, the first pure tone  RAREFACTION – speaker diaphragm moves back in  pull air  All additional tones (HARMONICS) must be a multiple of molecules in to fill gap, decrease air pressure the fundamental frequency  Repetition thousands time per second  pattern of alternating o FREQUENCY SPECTRA – another way to represent the harmonic high-low pressure regions in air spreads out  SOUND WAVE components of a complex tone  B/c neighboring air molecules affect each other  Horizontal position = frequency; Vertical position = amplitude  Air pressure changes moving outwards from sound source  Air molecules in medium moves back/forth  Osculates around point but stays around same place  Pressure changes: Pure Tones o PURE TONES – occurs when pressure changes in air occur in a pattern described by a SINE WAVE mathematical function  Ex. tuning forks, high pitched notes  Can be described by particular amplitude and frequency o AMPLITUDE – the size of the pressure change  Physical property of amplitude associated w/ experience of Perceiving sound loudness; higher amplitude = louder sounds  LOUDNESS – most closely associated w/ amplitude or sound pressure, level of auditory stimulus; associated w/ dB  Measured in DECIBELS (dB) – logarithmic scale of measurement o Increase sound by 10dB = roughly double loudness  dB SPL = 20 * log(p/p ) 0  where, p = sound pressure of the stimulus  Decibels = physical measure  air pressure  and, p = 20 micropascals, standard sound pressure,  Loudness = physiological  a perception 0 pressure near the threshold for human hearing  SPL (SOUND PRESSURE LEVEL) indicates we used the standard pressure of 20 micropascals as p0  PITCH – the attribute of auditory sensation in terms of which sounds may be ordered on a musical scale  perceptual quality of “high” or “low” o Closely related to physical property of frequency o FREQUENCY – number of times per sec. the pressure change repeats  Low fundamental frequencies associated w/ low pitch  Physical property of frequency associated w/ experience of pitch; higher frequency = higher pitch  High fundamental frequencies associated w/ high pitch  Measured in Hertz (Hz) – Hz is number of cycle per second o TONE HEIGHT – perceptual experience of increasing pitch that accompanies increases in a tone’s fundamental frequency  Humans can perceive in 20 – 20 000 Hz range  Increase in tone height show repetition of notes: A, B, … , F, G o Pure tones rare in environments but simple to study  Usually sound in environment have more complex waveforms  TONE CHROMA – the same for notes w/ same letter, same fundamental frequencies multiples of one another  Octave – an interval A through G o Pitch not determined by presence of fundamental frequency  but by info in it: such as spacing of the harmonics, the repetition rate of the waveform that indicates the fundamental frequency o EFFECT OF THE MISSING FUNDAMENTAL – the constancy of pitch even when the fundamental or other harmonics are removed  PERIODICITY PITCH – the pitch we perceive in tones that has had harmonics removed  THE RANGE OF HEARING – we hear sound only w/i specific range of freq. o Although frequencies of the harmonics always multiples of o THE AUDIBILITY CURVE –indicates the threshold for hearing fundamental frequency, harmonics may be absent determined by free-field presentation (loudspeaker) vs. frequency o Timbre also dependent on a tone’s  Range of hearing btwn 20 Hz and 20 000 Hz, we’re most  ATTACK – the buildup of sound at the beginning of the tone sensitive at frequencies between 2000 and 4000 Hz  DECAY – decrease in sound at the end of the tone  AUDITORY RESPONSE AREA (in green) – can hear tones that fall  Ex. piano and organ’s attack & decay inversed within this areas  Play one backwards, sounds like the other  Intensities below AUDIBILITY CURVE, can’t hear tone  THRESHOLD OF FEELING – can “feel”, painful, damaging The ear  The OUTER EAR – where sound waves first pass through o PINNA – structure that stick out form the side of head o AUDITORY CANAL – tube like structure, 3m long, protects the delicate structures of middle ear from hazards o TYMPANIC MEMBRANE (eardrum) – at the end of the canal, help keep the membrane and structures in middle ear at constant temp.  When airborne sound waves reaches tympanic membrane, they
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