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Hearing Detection Loudness Localization Scene Analysis Music Speech

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

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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

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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!

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

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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

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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)

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

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

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

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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 its hard to tell how loud your iPod is - LOCK THE VOLUME ON YOUR iPOD!

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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 Auditory Scene Analysis

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

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There are several clues you could use: Localization

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Left Ear Right Ear Compression Waves

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There are several clues you could use: 1 arrival time - sound arrives first at ear closest to source Localization

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Left Ear Right Ear Compression Waves

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There are several clues you could use: 1.arrival time 2.phase lag (waves are out of sync) - wave at ear farthest from sound source lags wave at ear nearest to source Localization

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Left Ear Right Ear Compression Waves

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There are several clues you could use: 1.arrival time 2.phase lag (waves are out of sync) - wave at ear farthest from sound source lags wave at ear nearest to source 3.Head shadow Localization

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Arrival Time Phase Lag Head Shadow Interaural Timing Differences (ITD) Interaural Intensity Difference (IID)

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What are some problems or limitations? Localization

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Low frequency sounds arent attenuated by head shadow Localization Left Ear Right Ear Compression Waves Sound is the same SPL at both ears

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Low frequency sounds arent attenuated by head shadow Your brain preferentially uses ITD cues for low-frequency sounds Localization

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

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

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

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Localization Additional cues:

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

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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

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Localization What would be the worst case scenario for localizing a sound?