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

frequency - are sounds with only one 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

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

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

up position down What are harmonics?

imagine a guitar string:

up position down What are harmonics?

imagine a guitar string:

What are harmonics?

But more than one frequency can “fit” between the end points up position time -> down

up position What are harmonics?

In fact many frequencies can be

superposed

.

f 0 f 2 time -> down f 1

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

called (i.e. several things one on top of the other) of many related frequencies

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 • f 1 = 400 f 2 – (f 2 = 800 = 2 x f 1 )…octave • f 1 = 400 f 2 – (f 2 = 600 = 3/2 x f 1 )…perfect 5th • f 1 = 500 f 2 – (f 2 = 800 = 8/5 x f 1 )…minor 6th • f 1 = 400 f 2 – (f 2 = 550 = 11/8 x f 1 ) 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 4 notes/6 intervals (major 7) 3 notes/3 intervals 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

should match one and only one pattern in the spectrogram says that phonemes –This is not the case! For example /d/ followed by different vowels:

Perceiving Speech •

Acoustic - Phonetic invariance

should match one and only one pattern in the spectrogram says that phonemes –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”.

car”.

Perception (of all types) Makes Use of

Context

• Consider the following example:

shoe”.

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

cross modal 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

• Vision Next Time: