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What do we hear?

What do we hear?. Sound is a compression wave - it only “looks” like a wave if we plot air pressure against time. Period - amount of time for one cycle. Frequency = number of cycles per second (1/Period). Air Pressure. time ->. Sensing Vibrations. Inside the cochlea is the basilar membrane

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What do we hear?

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  1. What do we hear? • Sound is a compression wave - it only “looks” like a wave if we plot air pressure against time Period - amount of time for one cycle Frequency = number of cycles per second (1/Period) Air Pressure time ->

  2. Sensing Vibrations • Inside the cochlea is the basilar membrane • Movement of the oval window causes ripples on the basilar membrane

  3. Hearing • Detection • Loudness • Localization • Scene Analysis • Music • Speech

  4. Detection and Loudness • Sound level is measured in decibels (dB) - a measure of the amplitude of air pressure fluctuations

  5. Detection and Loudness • Sound level is measured in decibels (dB) - a measure of the amplitude of air pressure fluctuations • dB is a log scale - small increases in dB mean large increases in sound energy

  6. Detection and Loudness • Sound level is measured in decibels (dB) - a measure of the amplitude of air pressure fluctuations • dB is a log scale - small increases in dB mean large increases in sound energy • We have a dynamic range that is a factor of 7.5 million!

  7. Detection and Loudness • minimum sound level necessary to be heard is the detection threshold

  8. Detection and Loudness • detection threshold depends on frequency of sound: • very high and very low frequencies must have more energy (higher dB) to be heard • greatest sensitivity (lowest detection threshold) is between 1000 hz to 5000hz

  9. Detection and Loudness • Detection can be compromised by a masking sound • even masking sounds that are not simultaneous with the target can cause masking (forward and backward masking)

  10. Detection and Loudness • Loudness is the subjective impression of sound level (and not identical to it!)

  11. Detection and Loudness • For example, tones of different frequencies that are judged to be equally loud have different SPLs (dB)

  12. Detection and Loudness • Hearing loss due to exposure to high-intensity sounds (greater than 100 dB) is frequency-specific and can last many hours

  13. Detection and Loudness • Incidence of noise-related hearing loss is increasing dramatically • iPods and other “earbud” music players are thought to be partly responsible • How loud is an iPod? • maximum volume is approximate but is somewhere between 100 dB (hearing damage in about 2 hours) to 115 dB (hearing damage in about 15 minutes) • Consequences: difficulty understanding speech, tinnitus, deafness • Your perception of loudness adapts so it’s hard to tell how loud your iPod is - LOCK THE VOLUME ON YOUR iPOD!

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