Syllables and Stress October 21, 2015

What is Stress? Examples of stress in English: (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

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

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

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 Write the steps on the board.

RMS example A small sampling of a “sinewave” has the following pressure values: It looks like this (in Excel): Write the values on the board; Then calculate RMS amplitude before going to next slide. Work it all out by hand, slowly.

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

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

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

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.

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

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 Bold = sustained exposure can cause hearing damage Red = pain, immediate damage

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

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.”

From Ladefoged

A Sonority Scale low vowels high vowels glides high sonority liquids nasals fricatives stops high sonority low sonority Write this on the board

Sonority and Syllables An old idea (e.g., Pike, 1943): syllables are organized around peaks in sonority. This is the Sonority Sequencing Principle (SSP). Example: [bæd] is a well-formed syllable in English. [æ] [b] [d] high sonority low sonority

Sonority and Syllables An old idea (e.g., Pike, 1943): syllables are organized around peaks in sonority. This is the Sonority Sequencing Principle (SSP). Example: [blænd] works well, too. [æ] [l] [n] [b] [d] high sonority low sonority

Technical Terms sonority peak [æ] [l] [n] [b] [d] high sonority low sonority

Technical Terms The sonority peak forms the nucleus of the syllable. [æ] [l] [n] [b] [d] nucleus high sonority low sonority

Technical Terms The sonority peak forms the nucleus of the syllable. The sounds that precede the nucleus form the syllable onset. [æ] [l] [n] [b] [d] onset high sonority low sonority

Technical Terms The sonority peak forms the nucleus of the syllable. The sounds that precede the nucleus form the syllable onset. The sounds that follow the nucleus form the syllable coda. [æ] [l] [n] [b] [d] coda high sonority low sonority

Technical Terms The sonority peak forms the nucleus of the syllable. The sounds that precede the nucleus form the syllable onset. The sounds that follow the nucleus form the syllable coda. Together, the nucleus and coda form the syllable rhyme. [æ] [l] [n] [b] [d] rhyme high sonority low sonority

Syllables “defined” “Syllables are necessary units in the organization and production of utterances.” (Ladefoged, 1982) The construct of a “syllable” can account for a variety of interesting phonological patterns: Vowel reduction in unstressed syllables in English. Fricatives and stops devoice at the end of syllables in German, Russian (and many other languages) Place contrasts disappear in coda position in Japanese (and many other languages) Voiceless stops are aspirated at the onset of stressed syllables in many Germanic languages.

Back to Stress Stress is a suprasegmental property that applies to whole syllables. Stressed syllables are higher in pitch (usually) Stressed syllables are longer (usually) Stressed syllables are louder (usually) Stressed syllables reflect more phonetic effort. The combination of these factors give stressed syllables more prominence than unstressed syllables.

Stress: Pitch (N) (V) Complicating factor: pitch tends to drift downwards at the end of utterances

Stress: Intensity (N) (V) Perception of stress is highly correlated with the area under the intensity curve

“Phonetic Effort” Voiceless stops are more aspirated at the onset of stressed syllables in English Vowels are often reduced to in unstressed syllables in English. There is less coarticulation across syllable boundaries in stressed syllables. X-Ray microbeam study (deJong et al., 1993); two utterances: I said put the TOAST on the table, not the napkins! I said PUT the toast on the table, don’t throw it!

X-ray microbeam data

Varying Levels of Stress/Prominence English has both primary and secondary stress. Example: “exploitation” vowel X X X X full vowel X X X stress X X tonic accent X