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
Localization
•
1
There are several clues you could
use:
arrival time - sound arrives first at ear
closest to source
Localization
Left Ear
Right Ear
Compression
Waves
Localization
•
1.
2.
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
Localization
Left Ear
Right Ear
Compression
Waves
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
High frequency sounds have
ambiguous phase lag
Left Ear
Right 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
Auditory Scene Analysis
• Sounds don’t happen in isolation, they
happen in streams of changing
frequencies
• How does the system group related
auditory events into streams and keep
different streams separate?
Auditory Scene Analysis
• Solving this problem is called Auditory
Scene Analysis
• One important principle is proximity –in
pitch, time, or spatial location
Auditory Scene Analysis
• Effect of timing proximity:
Slow
Fast
Auditory Scene Analysis
• Effect of timing proximity:
Slow
Fast
Do you hear this?
Or this?
Auditory Scene Analysis
• Effect of pitch proximity:
far
close
Auditory Scene Analysis
• Effect of pitch proximity:
Do you hear this?
Or this?
far
close
Auditory Scene Analysis
• Effect of proximity:
– auditory system groups together events
that happen close together in time and
frequency
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