WebCT
You will find a link to WebCT under the “Current Students” heading on
www.uleth.ca. It is your responsibility to know how to work WebCT!
There is a practice test available online. Log in to WebCT from any computer to
take the test if you feel uncomfortable with WebCT (you don’t have to take the test if
you don’t want!).
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
• Tones that have the same Chroma are
octaves apart
• Tones that are octaves apart have the same
chroma
Chroma
• Tones that have the same Chroma are
octaves apart
• 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
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
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
Timbre (pronounced like:
Tamber)
Pronounciation of “timbre”
• pure tones are very rare
• a single note on a musical instrument is a
superposition (i.e. several things one on top
of the other) of many related frequencies
called harmonics
Timbre
• the characteristic of a particular set of
harmonics is called timbre
– e.g. the set of harmonics generated when a
particular key is pressed on a piano
• timbre is why we can tell the difference
between the same notes played on
difference instruments
Timbre
• Although any musical “note” is a
superposition of harmonics, you still hear it
as a single pitch (tone height)
• The pitch that you hear is (usually) the
fundamental frequency
Musical Intervals
• in music, notes are played together or in
quick succession
• pairs of notes share a relationship called an
interval
Musical Intervals
• Within each pair, the higher pitch (f2) is
some multiple of the lower pitch (f1):
– e.g. 200 hz and 400 hz -- f2 is two times f1
Musical Intervals
• f1= 400 f2 = 800
– (f2 = 2 x f1)…octave
• f1= 400 f2 = 600
– (f2 = 3/2 x f1)…perfect 5th
• f1= 500 f2 = 800
– (f2 = 8/5 x f1)…minor 6th
• f1= 400 f2 = 550
– (f2 = 11/8 x f1)
octave
perfect 5th
minor 6th
not quite a perfect
fourth?!
Consonance and Dissonance
• Consonance is the degree to which two
tones played together sound “good”
• Dissonance is the opposite
Consonance and Disonance
• Consonance
seems to
decrease
with
increasing
complexity
of the ratio
of the tones
Music is combinations of intervals
played in series (with some rhythm)
• Combination of three different intervals is a
chord (major or minor)
major
minor
• Additional intervals modify the sound of the
chord
3 notes/3 intervals
4 notes/6 intervals
(major 7)
4 notes/6 intervals
(dominant 7)
The Perception of Speech
Speech
•Speech is for rapid communication
•Speech is composed of units of sound called
phonemes
–examples of phonemes: /ba/ in bat , /pa/ in pat
Acoustic Properties of Speech
•Speech can be characterized by a spectrogram
Acoustic Properties of Speech
•Spectrogram reveals differences between phonemes
Perceiving Speech
• So perceiving (interpreting) speech sounds
is simply a matter of matching the
spectrotemporal properties (the shape of the
spectrogram) of the incoming sound waves
to the appropriate phoneme
• right?…
Perceiving Speech
• So perceiving (interpreting) speech sounds
is simply a matter of matching the
spectrotemporal properties (the shape of the
spectrogram) of the incoming sound waves
to the appropriate phoneme
• Then specific phonemes must correspond to
specific spectrograms - a property called
acoustic-phonetic invariance
Perceiving Speech
•Acoustic - Phonetic invariance says that phonemes
should match one and only one pattern in the
spectrogram
–This is not the case! For example /d/ followed by different
vowels:
Perceiving Speech
•Acoustic - Phonetic invariance says that phonemes
should match one and only one pattern in the
spectrogram
–This is not the case! For example /d/
•Clearly perception and understanding of speech
sounds is more elaborate than simply interpreting an
internal spectrogram
Perceiving Speech
•The phrase “Peter buttered the burnt toast” has
five /t/ phonemes. There are not 5 identical sweeps
in the spectrogram
Perceiving Speech
•Segmentation is the perception of silence
between words
•Often illusory
Perceiving Speech
•The phrase “I owe you a Yo-Yo” has no silence in it
!
Perceiving Speech
• So how do you perceive speech?
Perceiving Speech
• So how do you perceive speech?
Some of the “strategies”:
1. reduce the data
2. use context clues
3. use vision
Categorical Perception Sifts
through the Incoming Sound
•Categorical Perception is a phenomenon in
which the brain assigns a stimulus into one or
another category but never into an
intermediate category
Categorical Perception
•For example, /ba/ and /pa/ differ in their
formant transitions
–/ba/ is formed by stopping the flow of air from the
lungs and releasing it after about 10 ms. (called
voice onset time)
–/pa/ is similar except that voice onset time is about
50 ms
Categorical Perception
•Voice onset time can range from zero to >50
ms. For example, you could synthesize a
sound with a voice onset time of 30 ms but...
Categorical Perception
•Voice onset time can range from zero to >50
ms. For example, you could synthesize a
sound with a voice onset time of 30 ms but...
•Listeners will hear either /ba/ or /pa/ but
never something in between
Categorical Perception is Part of
Learning a Language
• Babies can discriminate /ba/ from /pa/ and
can discriminate these from phonemes with
intermediate voice onset times!
• By 10 to 12 months, babies (learning
English) stop discriminating intermediate
voice onset times
Categorical Perception is Part of
Learning a Language
• Once category boundaries are learned it is
impossible to unlearn them
– non-native speakers can often never hear
certain phonemes
– as a consequence they will always have at least
some slight accent
Categorical Perception
•Another example:
Perception (of all types) Makes
Use of Context
• The stream of information contained in
speech is usually ambiguous and incomplete
• Your brain makes a “best guess” based on
the circumstances
Perception (of all types) Makes
Use of Context
• Consider the following example:
shoe”.
“The __eel fell of the
cough
car”.
Perception (of all types) Makes
Use of Context
• Consider the following example:
shoe”.
“The __eel fell of the
cough
car”.
• Listeners report hearing the “appropriate”
phoneme during the cough
Much of Speech Perception isn’t
Auditory !
•Why rely on only one sensory system when
there is information in two !?
Much of Speech Perception isn’t
Auditory !
•Why rely on only one sensory system when
there is information in two !?
•The brain seamlessly integrates any
information it is given - this is called crossmodal integration
Cross-modal Integration
•Speech perception involves the synthesis of
vision and hearing
•The McGurk effect demonstrates the critical
role of vision on speech perception
Cross-modal Integration
QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
•The McGurk Effect
Next Time:
• Vision