• defining and measuring waves • classifying waves • basic...

Linguistic Phonetics M Aug 17

• Defining and measuring waves• Classifying waves • Basic (periodic) wave properties

Background reading:

• AAP Ch 1, through the end of sec 1.3.1

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0. Some Zoom reminders for LING 520

• During class:

- Turning your camera on is optional- Please mute your microphone unless you want to talk - You may also use the chat to ask and answer questions

*** Always join Zoom via unc.zoom.us ***(if necessary, give email as [...]@email.unc.edu)

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0. Today’s plan

• Quick check-in on course logistics

• Defining waves

• Measuring and graphing waves

• Classifying waves:- Simple periodic waves (sine waves)- Complex periodic waves- Aperiodic waves

• Basic properties of periodic waves

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1. Checking in on course logistics

• Course structure: Any questions or concerns? M — Zoom lecture [ LING 520 Zoom links and tips ]

- Lecture outline (slides) also available [ Daily syllabus ]- Recording with captions posted within about one day

W — Self-paced learning [ info and schedule ]

F — Lab sessions- Last week and this week (at least): Optional

synchronous working session / help session - In future weeks: Synchronous in groups by rotation;

asynchronous for other students

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https://users.castle.unc.edu/~jlsmith/ling520/remote.htmlhttps://users.castle.unc.edu/~jlsmith/ling520/online.htmlhttps://users.castle.unc.edu/~jlsmith/ling520/syllabus.html


• Your score from each week’s learning assignment will typically be visible by Friday in Sakai T&Q

- Each assignment states what score is “passing”

- Important: Even if you passed, take a look at the feedback for questions where you missed points and make sure you understand why

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• A lot of people missed this one:True or false? “...articulatory phonetics is concerned

with how the vocal organs move to produce eachletter in a word.”

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• A lot of people missed this one:True or false? “...articulatory phonetics is concerned

with how the vocal organs move to produce eachletter in a word.”

Always remember:

SOUNDS, NOT LETTERS

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2. What is a wave? What is a sound wave?

• A wave is a disturbance that propagates through amedium

• What are some real-life examples of waves? Describe them in the above terms:- What is the medium?- What property of the medium is being

disturbed?

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• See these wave animations by Dan Russell, Graduate Program in Acoustics, Penn State - People doing “the wave”- Air molecules inside a tube- A pulse of displacement moving along a string

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https://www.acs.psu.edu/drussell/Demos/waves-intro/waves-intro.html



• Important: The disturbance propagates; the piecesof the medium do not- When sports fans do “the wave”, they stay in

their own seats- When air molecules vibrate, they move slightly

back and forth, but they don’t travel to the end of the tube

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• What is sound?In AAP, p 7, Johnson defines sound as a sensation

Motion of object →pressure fuctuations in medium →pressure fuctuations reach eardrum →neural transmission →perception/sensation of sound

- If a tree falls in the forest when no one is there, does it make a sound (according to this definition)?

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• Where is the sound wave in this chain of events?Motion of object →pressure fuctuations in medium →pressure fuctuations reach eardrum →neural transmission →perception/sensation of sound

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• Where is the sound wave in this chain of events?Motion of object →pressure fluctuations in medium →pressure fuctuations reach eardrum →neural transmission →perception/sensation of sound

- If a tree falls in the forest when no one is there, does it make a sound wave?

• Note: there can be no sound without motion11

3. Measuring waves: Time vs. space

• Think about waves in water - What is the medium? — the water- What is the disturbance?

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• Think about waves in water - What is the medium? — the water- What is the disturbance? — the height of

the water above/below the resting state

• How could we describe (graph) waves in a lake?- Look at this animation

by Dan Russell, Graduate Program in Acoustics, Penn State

- What does each graph of the wave represent?Note: You are not responsible for knowing the formula at the top of the page

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http://www.acs.psu.edu/drussell/Demos/wave-x-t/wave-x-t.html


• How could we describe (graph) waves in a lake?- We could plot water height by distance from

the disturbance at a single point in time (like a photograph of the water surface)

• This is the graph on the right

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• How could we describe (graph) waves in a lake?- We could plot water height over time for a

single point in space (imagine watching a measuringstick on the end of a dock in the lake)

• This is the graph on the left

• Always look at the axes on a graph when you are trying to interpret what it shows

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• Sound waves are different from water waves: sound waves are pressure waves - Look again: Animation of air inside a tube

by Dan Russell, Graduate Program in Acoustics, Penn State

• But, as with the water example, we can measure and graph sound waves in two different ways- Air pressure by distance from the source at a

single point in time - Air pressure by time at a single point in space

• Which of these is what a microphone does?16

https://www.acs.psu.edu/drussell/Demos/waves-intro/waves-intro.html


• Look at V&C Figure 1.1 (p 7):

• This is a sound wave (the axes aren’t explicitly labeled)- How does this display show that there is a

disturbance in a medium?

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4. Classifying waves

Preview of concepts for Wednesday

• Periodic — has a repeating pattern - Simple periodic — a sine wave

( sine wave)←

- Complex periodic — any other repeating pattern

• Aperiodic — no repeating pattern - Noise — aperiodic sound that persists in time- Transient — instantaneous aperiodic sound

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- Periodic or aperiodic?- Simple or complex?

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- Periodic or aperiodic? | repeating pattern?- Simple or complex? | sine wave, or other?

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5. Properties of periodic waves


• To describe a periodic wave (for speech analysis), the most relevant properties are…

Physical property (acoustics)

Human perception

frequency amplitude wave shape

pitch loudness quality (timbre)

• These factors can vary independently

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5. Properties of periodic waves


• Practice with sound waves in Praat: Consider the musical notes [1] and [2] - How do their frequencies compare?- How do their amplitudes compare?- How do their wave shapes compare?

from the Music Acoustics web site, UNSW

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https://newt.phys.unsw.edu.au/music/http://www.phys.unsw.edu.au/music/clarinet/sounds/C4.wavhttp://www.phys.unsw.edu.au/music/flute/baroque/sounds/C5.baroque.wav

• defining and measuring waves • classifying waves • basic...

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