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Hearing

Hearing. Detection Loudness Localization Scene Analysis Music Speech. Detection and Loudness. Sound level is measured in decibels (dB) - a measure of the amplitude of air pressure fluctuations. Detection and Loudness.

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Hearing

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

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

  3. 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

  4. 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!

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

  6. 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

  7. 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)

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

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

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

  11. 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!

  12. Auditory Scene Analysis • recall the lake analogy: task is to • localize the positions of the boats on a lake using the pattern of ripples at two points on the shore • Identify the sources of those ripples • Ignore non-relevant ripples

  13. Localization • All you have is a pair of instruments (basilar membranes) that measure air pressure fluctuations over time

  14. Localization • There are several clues you could use:

  15. Localization Left Ear Right Ear Compression Waves

  16. Localization • There are several clues you could use: • arrival time - sound arrives first at ear closest to source

  17. Localization Left Ear Right Ear Compression Waves

  18. Localization • There are several clues you could use: • arrival time • phase lag (waves are out of sync) - wave at ear farthest from sound source lags wave at ear nearest to source

  19. Localization Left Ear Right Ear Compression Waves

  20. Localization • There are several clues you could use: • arrival time • phase lag (waves are out of sync) - wave at ear farthest from sound source lags wave at ear nearest to source • Head shadow

  21. Localization • Arrival Time • Phase Lag • Head Shadow InterauralTiming Differences (ITD) InterauralIntensity Difference (IID)

  22. Localization • What are some problems or limitations?

  23. Localization • Low frequency sounds aren’t attenuated by head shadow Sound is the same SPL at both ears Left Ear Right Ear Compression Waves

  24. Localization • Low frequency sounds aren’t attenuated by head shadow • Your brain preferentially uses ITD cues for low-frequency sounds

  25. Localization • High frequency sounds have ambiguous phase lag Left Ear Left Ear Right Ear Right Ear Two locations, same phase information!

  26. Localization • High frequency sounds have ambiguous phase lag • Your brain preferentially uses IID cues for high-frequency sounds

  27. Localization • These cues only provide azimuth (left/right) angle, not altitude (up/down) and not distance Left Ear Right Ear Azimuth

  28. Localization Additional cues:

  29. Localization Additional cues: Head Related Transfer Function: Pinnae modify the frequency components differently depending on sound location

  30. Localization Additional cues: Room Echoes: For each sound, there are 6 “copies” (in a simple rectanguluar room!). Different arrival times of these copies provide cues to location of sound relative to the acoustic space

  31. Localization • What would be the “worst case” scenario for localizing a sound?

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