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Syllables and Stress

Syllables and Stress. October 25, 2010. Practicalities. Some homeworks to return… Review session on Wednesday. Mid-term on Friday. Note: transcriptions have been posted to the course web page. Let’s check out the Boston English sample. Review: Suprasegmentals.

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Syllables and Stress

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  1. Syllables and Stress October 25, 2010

  2. Practicalities • Some homeworks to return… • Review session on Wednesday. • Mid-term on Friday. • Note: transcriptions have been posted to the course web page. • Let’s check out the Boston English sample.

  3. Review: Suprasegmentals • Last time, we learned that there were three kinds of languages: • Tone languages (Chinese, Navajo, Igbo) • lexically determined tone on every syllable or word 2. Accentual languages (Japanese, Swedish) • the location of an accent is lexically marked. 3. Stress languages (English, Russian) • it’s complicated

  4. What is Stress? • Examples of stress in English: • (V) vs. (N) • (V) vs. (N) • Phonetically, stress is hard to define • I.e., it is hard to measure. • It seems to depend on an interaction of three quantifiable variables: • Pitch • Duration • Loudness • And also: quality

  5. Loudness • How do we measure how loud a sound is? • Recall: one parameter of a sinewave is its amplitude. • Peak amplitude (for sound) is the highest sound pressure reached during a particular wave cycle. peak-to-peak amplitude

  6. Amplitude/Loudness Examples • The higher the peak amplitude of a sinusoidal sound, the louder the sound seems to be.

  7. RMS amplitude • Peak-to-peak amplitude is sufficient for characterizing the loudness of sinewaves, but speech sounds are more complex. • Another method of measuring loudness: • root-mean-square (RMS) amplitude • To calculate RMS amplitude: • Square the pressure value of the waveform at each point (sample) in the sound file • Average all the squared values • Take the square root of the average

  8. RMS example • A small sampling of a “sinewave” has the following pressure values: • It looks like this (in Excel):

  9. RMS calculations • To calculate RMS amplitude for this sound, first square the values of each sample: • Then average all the squared values • (1 + .5 + 0 + .5 + 1 + .5 + 0 + .5 + 1) / 9 = 5/9 = .555 • Then take the square root of the average • RMS amplitude = .745

  10. Another example • What about the RMS amplitude of this sound wave? • It looks like this (in Excel):

  11. More Complex Waveforms • The following waveforms all have the same peak-to-peak amplitude:

  12. Intensity • Two related concepts are acoustic power and intensity. • Power is just the square of amplitude. • P = A2 • The intensity of a sound is its power relative to the power of some reference sound. • Intensity is usually measured in decibels (dB). • Decibels is a measure of intensity with reference to the quietest sound human ears can hear.

  13. Some Numbers • The intensity of a sound x can be measured in bels, where a bel is defined as: • = log10 (x2 / r2) • r2 is the power of the reference sound • x2 is the power of sound x. • A decibel is a tenth of a bel. • Some typical decibel values: • 30 dB Quiet library, soft whispers • 40 dB Living room, refrigerator • 50 dB Light traffic, quiet office • 60 dB Normal conversation

  14. Numbers, continued • Some typical decibel values: • 70 dB Vacuum cleaner, hair dryer • 80 dB City traffic, garbage disposal • 90 dB Subway, motorcycle, lawn mower • 100 dB Chain saw, pneumatic drill • 120 dB Rock concert in front of speakers, thunderclap • 130 dB Pain threshold • 140 dB Gunshot blast, jet plane • 180 dB Rocket launching

  15. Intensity Interactions • Perceived loudness depends on frequency, as well as amplitude. • Mid-range frequencies sound louder than low or extremely high frequencies. • 100 Hz • 250 Hz • 440 Hz • 1000 Hz • 4000 Hz • 10000 Hz

  16. An Interesting Fact • Some vowels are louder than others • dB of different vowels relative to (Fonagy, 1966): • : 0.0 • [e] : -3.6 • [o] : -7.2 • [i] : -9.7 • [u] : -12.3 • Why?

  17. Another Interesting Fact • Some vowels are inherently longer than others. • Data from Swedish (Elert, 1964): • long short • high [i y u] 140 msec 95 • mid 155 103 low 164 111 • Why?

  18. Sonority • Loudness is also a highly context-dependent measure. • Can vary wildly within speaker, from speaker to speaker, from room to room, and across speaking contexts. • However, all things being equal, some speech sounds are louder than others. • Course in Phonetics: • “The sonority of a sound is its loudness relative to that of other sounds with the same length, stress and pitch.”

  19. From Ladefoged

  20. A Sonority Scale • low vowels • high vowels • glides • liquids • nasals • fricatives • stops high sonority low sonority

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