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 Localization

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

Left Ear Right Ear Compression Waves

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

Left Ear Right Ear Compression Waves

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

Left Ear Right Ear Compression Waves

What are some problems or limitations? Localization

Low frequency sounds aren’t attenuated by head shadow Localization Left Ear Right Ear Compression Waves Sound is the same SPL 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?

Pitch and Music

Pitch Pitch is the subjective perception of frequency time -> Air Pressure Period - amount of time for one cycle Frequency - number of cycles per second (1/Period)

Pitch Pure Tones - are sounds with only one frequency f = 400 hz f = 800 hz

Tone Height Tone Height is our impression of how high or low a sound is but there’s something more to our impression of how something sounds than just its tone height…

Chroma Tone Chroma is the subjective impression of what a tone sounds like Notes that have the same Chroma sound similar 400 hz 500 Hz 800 Hz

Chroma Tones that have the same Chroma are octaves apart

Chroma chroma is best represented as a helix chroma repeats every octave tones with the same chroma are above or below each other on a helix

Chroma Tones that are octaves apart have the same chroma one octave is a doubling in frequency

Chroma frequency is determined (in part) by location of stimulation on the basilar membrane

Chroma frequency is determined (in part) by location of stimulation on the basilar membrane but that relationship is not linear (it’s logarithmic)

Chroma doublings of frequency map to equal spacing on the basilar membrane

Pure Tones are Very Rare in Nature! What are real sounds composed of?

Pure Tones are Very Rare in Nature! What are real sounds composed of? Virtually all sounds are composed of several (or many) frequencies all going at once

Pure Tones are Very Rare in Nature! What are real sounds composed of? Virtually all sounds are composed of several (or many) frequencies all going at once “Extra” frequencies are called harmonics