Phonetics

CS 551/652: Structure of Spoken Language Lecture 2: Spectrogram Reading and Introductory Phonetics John-Paul Hosom Fall 2008

Spectrogram Reading
Why bother??
What’s the point of spectrogram reading? Do people read
spectrograms as part of their job? Do computers “read” spectrograms
in order to recognize speech?
There are some jobs that require spectrogram reading (e.g. phonetic
time alignment), but not many. Automatic speech recognition
systems do not process speech in this way.
Primary reason for spectrogram reading:
If you’re going to work on a problem, it’s advisable to
understand the nature of that problem. Spectrogram reading
provides a direct method for “hands-on” learning of the
characteristics of speech. Studying phonetics, signal processing,
or techniques in speech recognition/speech synthesis does not
fully convey of the complexity and structure of spoken language.

A great website on spectrogram reading: http://home.cc.umanitoba.ca/~robh/ includes “how to” tips on spectrogram reading, a monthly “mystery spectrogram”, and archives of past months’ spectrograms.

Phonetics: Introduction Phonology: A description of the systems and patterns of sounds that occur in a language (abstract), often involving comparisons between languages and/or evolution of a language over time. Phonetics: A branch of phonology that deals with individual speech sounds, their production, and their written representation. Phoneme: • A unit of speech that can be used to differentiate words (e.g. “cat” /k ae t/ vs. “bat” /b ae t/). • Phonemes identify minimal pairs in a language. • The set of phonemes in a language subject to interpretation; most languages have 20 to 40 phonemes.

Phonetics: Introduction Allophone: A speech sound constituting one of the systematic phonetic variants of a given phoneme. Different allophones are predictable from environment (e.g. “toe”, “caught”, “fitness”, “writer”; “sill”, “still”, “spill”) Phone: An acoustic realization of a phoneme. (Many different phones may represent the same phoneme.) “The phoneme /s/ consists of more than 100 allophones” − Pickett, The Acoustics of Speech Communication , p. 7. Phonemes indicated by / /; phones (allophones) indicated by [ ].

Phonetics: Introduction Syllable: • Unit of speech containing one or more phonemes. • A vowel in a syllable is called the syllable nucleus . • Most syllables contain one vowel (or diphthong); some contain only a lateral (“bott/le”) or nasal (“butt/on”) as the most intense sound. • Syllable boundaries sometimes ambiguous (“tas/ty” vs. “tast/y” vs. “ta/sty”) Coarticulation: The “blending” of two or more adjacent phones, causing a non-distinct boundary between them. Coarticulation is caused by smooth changes in the articulators (lips, tongue, jaw) over time.

Phonetics: Introduction Coarticulation Example: y uw aa r “ you are”: /y uw aa r/

Phonetics: Introduction (adapted from Schane, p. 4-6)
Speech signal is continuous; we perceive discrete entities.
(How many sound units are in the word “cat”?)
One assumption of phonology: utterances can be represented as
sequence of discrete units.
Are such units purely an “invention” of linguistics?
Spoonerisms (“belly jeans” vs. “jelly beans”) and rhymes indicate small units of language (Reverend William Archibald Spooner (1844-1930))
Utterances of the same word(s) have many differences… we’re
usually only interested in those differences that are “linguistically
significant” or that are “perceived as different”.
Implies a somewhat subjective nature to phonology, whereas
we want an objective measure of perceived or produced units.

Phonetics: Distinctive Phonetic Features • Phonemes do not differ randomly from one another; there are relationships among phonemes (e.g. /p/ vs. /t/ vs. /ah/) • A (distinctive) feature is a “phonetic property that can be used to classify sounds” [Ladefoged, p. 42] • Typically, features are associated with aspects of articulation • Features may be binary or multi-valued • Capital letters indicate feature name: Manner square brackets [] indicate feature value: [+fricative]

Phonetics: Distinctive Phonetic Features
• Exact set of features and feature values depends on goals
(no “right” or “wrong” set of features or values)
• Distinctive features provide a vocabulary for describing speech
• Are distinctive features purely an “invention” of linguistics?
memory tasks show that when people forget a phoneme, they usually remember a phoneme with similar distinctive features

Phonetics: Distinctive Phonetic Features nasal tract (hard) palate oral tract velum (soft palate) velic port tongue tongue tip pharynx glottis (vocal folds and space between vocal cords) vocal folds (larynx) = vocal cords alveolar ridge lips teeth The Speech Production Apparatus (from Olive, p. 23)

Phonetics: Distinctive Phonetic Features * Feature Description _ Consonantal produced with a constriction along center line of oral cavity. Only vowels, /w/, /h/, and /y/ are not. Vocalic largely unobstructed vocal tract. Vowels and liquids (/l/, /r/) are vocalic; glides (/w/, /y/) are not. Anterior point of articulation near alveolar ridge, including all labial and dental sounds. Coronal articulation involves front of tongue Continuant no complete obstruction in oral cavity; only nasals, stops, and affricates are non-continuant Strident articulation with long, narrow constriction; such as /s/, /z/, /f/, /v/, /sh/, /zh/, /ch/, /jh/ Voiced vibration of the vocal folds occurs during articulation

Phonetics: Distinctive Phonetic Features * Feature Description _ Lateral contact between corona of tongue and roof of mouth, with lowering of sides of tongue (only /l/ in English) Nasal lowering of the velic port and opening of nasal cavity. High vowel with high tongue position (narrow constriction); in English, /iy/, /ih/, /uh/, /uw/ Low vowel with low tongue position (no constriction); /ae/, /ao/, /aa/ are (some) low vowels in English. Back vowels produce with tongue toward back of mouth; /uw/, /uh/, /ah/, /ao/, /aa/, /ow/ are back vowels Round articulation involving rounding of the lips; only /uw/, /ow/, /ao/, and /uh/ are rounded in English. However, /uh/ may take an unrounded form. * Adapted from “Language” by C.E.Cairns and F. Williams in Normal Aspects of Speech, Hearing, and Language , edited by Minifie, Hixon, and Williams, 1973, p. 424, as printed in Daniloff p. 51.

Phonetics: More Distinctive Phonetic Features * Feature Description _ Sonorant “resonant quality” of a sound; vowels are +sonorant, stops and fricatives are –sonorant. nasals also sonorant. Syllabic is the phoneme the main sound in a syllable? vowels are syllabic, stops are usually –syllabic, but there are syllabic nasals and liquids. Tense tense vowels are longer, more fully articulated, and more “distinct,” e.g. /iy ey uw ow aa/; lax vowels are less so, e.g. /ih eh uh ah/. Aspirated produced without a constriction in the vocal tract, but also without voicing (/h/). Glottalized produced with aperiodic or extremely low-frequency vibrations of the vocal cords. Diphthong a single phoneme composed of two or more other phonemes in sequence (/ay/, /oy/, /ei/, /aw/, /ow/) * from Schane, pp. 26-32

Phonetics: Distinctive Phonetic Features Physiological Features: • Manner stop /p/, fricative /s/, affricate /ch/, liquid /l/, /r/, glide /j/, /w/, nasal /m/, vowel /ah/, aspiration /h/ • Place bilabial /p/, labiodental /f/, dental /th/, alveolar /t/, palato-alveolar /r/, palatal /sh/, velar /k/, glottal /h/, front /iy/, mid /ah/, back /aa/ ( can combine mid + back) • Height high /iy/, mid-high /ih/, mid /ax/, mid-low /eh/, low /aa/ or high /iy/, mid /eh/, low /aa/ (3 values, plus tense/lax) • Tenseness, Nasality, Rounding same as previous descriptions

Phonetics: Distinctive Feature Relationships: Vowels * from Schane, pp. 12-13. † /ax/ is slightly more centralized than /ah/, and shorter in duration  (ao) a (aa) œ æ (ae) Low o (ow) ^ (ah) ö e (eh) Mid u (uw) i (ix) ü i (iy) High Rounded Unrounded Rounded Unrounded Back Front uh Lax ao ow uw Tense Back, +Round aa ae Low ah, ax † eh ey Mid ix ih iy High Lax Tense Lax Tense Back, –Round Front, –Round

Phonetics: Distinctive Phonetic Features: The Case of /ae/
/ae/ is classified in the preceding table as “lax”, but we have been considering it as “tense”.
One Rule for Differentiating Tense/Lax:
A lax vowel can never be a word-final stressed vowel
e.g. /iy/ can be word final: “be” /b iy/, “tea” /t iy/
/ih/ can not be word final in one-syllable word: /b ih/, /t ih/
/ah/ can be word final, but only if unstressed.
According to this rule, both /eh/ and /ae/ are lax, because they can not be word-final stressed vowels. In this case, the tense vowel in contrast to /eh/ is /ey/.
However, /ae/ is long in duration (e.g. Forgie and Forgie (1959) and Peterson and Lehiste (1960) ), making it acoustically more similar to a tense vowel.
For spectrogram reading, we’re more concerned with acoustics, so we’ll call /ae/ a tense vowel, although others may call it lax.

Phonetics: Distinctive Phonetic Features: The Case of /ae/
Looking at 130,000 words in the CMU dictionary:
PHN CNT PCNT EXAMPLES
/iy/ 12945 0.10002
/ih/ 15 0.00012 “chui”, “des”, “kiwani”, “lui”, “moishe”, “pih”, “ to ”
/eh/ 30 0.00023 “bienvenue”, “des”, “eh”, “moshe”, “yahweh”, “zeh”
/ae/ 5 0.00004 “dhaka”, “lashua”, “losoya”, “pah”, “ yeah ”
/uw/ 714 0.00552
/uh/ 2 0.00002 “l’heureux”, “milieu”
/ah/ 6413 0.04955
/aa/ 170 0.00131
/ao/ 243 0.00188
/ey/ 962 0.00743
/ay/ 379 0.00293
/oy/ 167 0.00129
/yu/ 171 0.00132
/aw/ 226 0.00175
/ow/ 5137 0.03969
0.21280 21% of words end in vowel/diphthong

Front Central Back High Mid Low iy ih eh ae ah aa ao uh uw ix ax ju ey ay aw ow Phonetics: Distinctive Feature Relationships: Vowels from Ladefoged, pp. 38, 81, 218 with correction to /aw/ oy

approximant obstruent Phonetics: Distinctive Feature Relationships: Consonants from Olive, p. 28 and Daniloff, p. 56 n l +voice lateral r +voice retroflex (w) y w +voice glides ng m +voice nasals ch -voice jh +voice affricates sh s th f -voice h zh z dh v +voice fricatives k t p -voice g d b +voice stops glottal velar palatal palato- alveolar alveolar dental labio-dental bilabial Voicing Manner

Phonetics: Distinctive Feature Relationships: Consonants from Ladefoged, p. 44 -anterior +anterior l +lateral approximant y r w -lateral th dh f v -sibilant fricative sh zh s z ch jh +sibilant k g t d p b -nasal stop ng n m +nasal -sibilant Dorsal Coronal Labial

Approximants: Terminology
“ Approximants” are NOT the same as “Semi-Vowels” (although Rabiner states they are the same…). American English /r/ is debatable, but we’ll exclude it from the Semi-Vowels for consistency. (Ladefoged p. 229)
Approximants can be divided into two groups: Liquids and Glides Liquid = {/l/, /r/}, Glide = {/w/, /y/} (Again, Rabiner confuses things by mixing up these sets)
Lateral = {/l/}
Retroflex = {/r/, /er/, /axr/}. (In some cases, /er/ is considered a retroflex but /r/ isn’t; we’ll keep things simple by calling /r/ a retroflex).
Central Approximants = {/r/, /w/, /y/}, Lateral Approximant = {/l/}

Approximants: Terminology Approximant Semi-Vowel / Glide Liquid Lateral Retroflex /y/ /w/ /r, er, axr/ /l/ central approximants lateral approximant

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Phonetics

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