Exam and Assignment Dates

• Midterm 1 Feb 3rd and 4th • Midterm 2 March 9th and 10th

• Final April 20th and 21st

• Idea journal assignment is due on last day of class

Textbooks• Sensation and Perception• Fundamentals of Sensation

• Cognition – Useful in a few weeks

• Course Pack – Will start in a couple weeks.

Useful Now

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

• 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

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!

Detection and Loudness

• minimum sound level necessary to be heard is the detection threshold

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

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)

Detection and Loudness

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

Detection and Loudness

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

Detection and Loudness

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

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!

• 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

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

Localization

• There are several clues you could use:

Localization

Localization

Left Ear

Right Ear

CompressionWaves

• There are several clues you could use:

1 arrival time - sound arrives first at ear closest to source

Localization

Localization

Left Ear

Right Ear CompressionWaves

• 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

Localization

Left Ear

Right Ear CompressionWaves

• What are some problems or limitations?

Localization

• Low frequency sounds aren’t attenuated by head shadow

Localization

Left Ear

Right Ear CompressionWaves

Sound is the sameSPL at both ears

• High frequency sounds have ambiguous phase lag

Localization

Left Ear

Right Ear

Left Ear

Right Ear

Two locations, same phase information!

• These cues only provide azimuth (left/right) angle, not altitude (up/down) and not distance

Localization

Left Ear

Right Ear Azimuth

Localization

Additional cues:

Localization

Additional cues:

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

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

Localization

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