Localization
•
1.
2.
3.
There are several clues you could
use:
arrival time
phase lag (waves are out of sync)
sound shadow (intensity difference)sound is louder at ear closer to sound
source
Localization
•
What are some problems or
limitations?
Localization
•
Low frequency sounds aren’t
attenuated by head shadow
Sound is the same
SPL at both ears
Left Ear
Right Ear
Compression
Waves
Localization
•
Left Ear
Right Ear
High frequency sounds have
ambiguous phase lag
Left Ear
Right Ear
Two locations, same phase information!
Localization
•
These cues only provide azimuth
(left/right) angle, not altitude
(up/down) and not distance
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
Period - amount of time for one cycle
Frequency - number of
cycles per second
(1/Period)
Air Pressure
time ->
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
500 Hz
400 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
What are harmonics?
imagine a guitar string:
up
position
down
What are harmonics?
imagine a guitar string:
up
position
down
What are harmonics?
But more than one frequency can “fit” between the end points
up
position
time ->
down
What are harmonics?
In fact many frequencies can be superposed.
up
f0
f2
position
time ->
down
f1
What are harmonics?
Superposition of two (or more) frequencies yields a complex
wave with a fundamental frequency
The Missing Fundamental
• Your brain so likes to track the
fundamental of a set of harmonics that it
will perceptually fill it in even when it is
absent
missing fundamental