Audition What are the 2 main components of sound and what are their psychological correlates Amplitude intensity Decibels dB next slide Corresponds to loudness Frequency Hertz Hz I Hz 1 cycle second So the air pressure in a 500 Hz wave goes from lowest to highest to lowest 500 times every second Humans hear from about 20 20 000 Hz Corresponds to pitch Why do we use a log scale for decibels The dB scale is a log scale describing sound pressure level SPL 0 dB is a reference point corresponding to the very quietest thing that a healthy ear could possibly hear Log scales compress a large range into a smaller range If a whisper has a level of 1 a jet engine has a level of 10 000 000 Remember what seems like a small change in decibels maybe 20dB can actually reflect a really huge change in sound pressure ie amplitude What is an audiogram What is a spectrogram What is a sonogram Audiogram a graph that shows the audible threshold for standardized frequencies as measured by an audiometer While audiograms are generated using pure tones as test stimuli real sounds are not pure tones they are complex sounds Spectrogram A spectrum displays the amplitude for each frequency present in a sound wave Each signal is shown as a waveform a and as a spectrum b The lowest frequency is the fundamental frequency The other frequencies present in the sound are called the harmonics Harmonic sounds w the same fundamental frequency so same pitch sound different b c the amplitudes of individual frequency components are different so they have different spectral shapes Right three instruments playing the same note middle C thus w the same fundamental frequency but perceptually they sound different they have their own unique timbre b c harmonics have different amplitudes Your vocal tract changes the spectrum of sound to form speech sounds Sonogram A spectrum plotted over time X axis represents time Y axis represents frequency Darkness of lines represents amplitude In a sonogram the sound pressure level is indicated by a gray color scale where the lowest and highest sound levels in the meow appear light gray and black respectively What is the difference between a pure tone and a complex tone Adding pure tone components can create a complex sound What are fourier analysis fourier synthesis Fourier Analysis Complex sounds can be broken down into their pure tone components Fourier Synthesis A complex sound can be created by adding pure tone components What is the fundamental frequency What are harmonics What is timbre and what does timbre have to do w harmonics Harmonic spectra spectrum of a complex sound in which energy is at integer multiples of the fundamental frequency caused by simple vibrating sources reed of a saxophone or string of guitar Fundamental frequency Harmonic Whole number multiple of the fundamental frequency A tone that is a component of a complex sound lowest tone in the harmonic series Harmonics are always evenly spaced multiples of the fundamental frequency so the higher the fundamental frequency pitch the further apart the harmonics will be pronounced tamber Perceptual quality of a complex sound altered by combinations of harmonics Timbre Why do different instruments playing the same note sound different Three instruments playing the same note middle C thus w the same fundamental frequency but perceptually they sound different they have their own unique timbre b c harmonics have different amplitudes In general what does the study of psychoacoustics tell us about the relationship between amplitude and loudness What about the relationship between frequency and pitch The study of the psychological correlates of the physical dimensions of acoustics Take home message Energy Perception A positive correlation exists it just isn t 1 1 Can you give examples of how amplitude and loudness differ from each other and of how frequency and pitch differ from each other Understand the term response compression Amplitude and loudness Higher amplitude louder sound would make it appear For a single contour tones of different frequencies have different physical intensities but they sound equally loud Web Exercise You can pick a frequency then adjust the amplitude and have listener judge how loudness changes Over 40 dB to double perceived loudness have to more than double acoustic energy So perception does not increase as fast as sensation Also longer sounds are heard as louder Why Temporal integration summation of energy over a brief but noticeable period of time Only occurs b t about 100 300 msec Sound for 100 ms sounds quieter than same sound for 300 ms No difference in perception of sound that lasts 300 ms Frequency and Pitch compared to 1000 ms We are very sensitive to changes in frequency Can discriminate b t 999 Hz vs 1000Hz Not as good at high low ends of frequency range Why actually why not For high end can t do temporal matching not even volley principle keeps up At the low end we aren t that sensitive anyway Increase a tone 500 Hz What does the subject perceive 500 Hz to 1000 Hz is perceived as a greater pitch difference than 5000 Hz to 5500 Hz This is similar to the Just noticeable difference the smallest amount that 2 things can be different and we can perceive the difference Response Compression Perception does not increase as fast as sensation What are equal loudness curves For a single contour tones of different frequencies have different physical intensities but they sound equally loud What are the major components of the outer middle and inner ear What membranes separate the middle ear from the outer ear and the inner ear Outer ear Tympanic membrane Pinna Ear canal Middle ear Inner ear Otolith organs Cochlea Semicircular canals Ossicles Oval window border b t middle inner ear What is the purpose of the pinna Only mammals have pinna Varies greatly b t species little bit w in species Important in localizing sound More in other critters than in humans but to some extent in Not the only part of the auditory system that does this in humans humans What is the function of the ossicles and know their names too Why is this function necessary how is it accomplished Ossicles malleus hammer incus anvil stapes stirrup They conduct sound vibrations from the eardrum across the middle ear into the fluid filled inner ear Inside the inner ear these vibrations are converted to nerve signals that are carried by the auditory nerve to the brain Amplify sound vibrations Joints b t bones make them work like levers
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