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Phoneme Model

Evan Kirshenbaum's feature set used in his ASCII transcription of the International Phonetic Alphabet (IPA)[1], [2] describes the phonemes in a way consistent with how the phonemes are organised in the IPA code chart. That is the approach used in the Phonemes document to describe the phonemes in a phoneme definition file.

Those phoneme features often represent the action of more than one articulatory mechanism used to produce speech, or affect the same area. Internally, espeak-ng makes use of the articulatory model, not the IPA descriptions. This document describes how the feature-based IPA model is mapped to the articulatory model.

People working on adding new voices or languages do not need to read this document, but should instead read the Phonemes document. This is intended for people working on the espeak-ng codebase, or people interested in how espeak-ng works internally.

NOTE: This model is in the process of being implemented. As such, the current implementation does not reflect this document.

Manner of Articulation

The manner of articulation is described in terms of several distinct feature types. The possible manners of articulation are:

Manner of Articulation Feature Phoneme Model
nasal nas pmc egs nsl occ
plosive (stop) stp pmc egs orl occ
affricate afr pmc egs orl occ frr
fricative frc pmc egs orl frv
tap/flap flp pmc egs orl fla
trill trl pmc egs orl tri
approximant apr pmc egs orl app
click clk vlc igs orl
ejective ejc vlc igs orl occ
implosive imp gtc igs
vowel vwl pmc egs orl vow

For imp consonants, they use the features of the base phoneme except for the pmc and egs features. Thus, a nas imp is a gtc igs nsl occ.

The vwl phonemes are described using vowel height and backness features, while consonants (the other manners of articulation) are described using place of articulation features.

Additionally, the manner of articulation can be refined using the following features:

Feature Name Description
lat lateral The air flow is directed along the sides of the tongue.
sib sibilant The air flow is directed through the teeth with the tongue.

Air Flow

Feature Name Description
egs egressive The air flow is moving outwards from the initiator to the target.
igs ingressive The air flow is moving inwards from the target to the initiator.

Initiator

Feature Name Description
pmc pulmonic The diaphragm and lungs are used to generate the airstream.
gtc glottalic The glottis is used to generate the airstream.
vlc velaric The velum is closed and the tongue is used to generate the airstream.
pcv percussive There is no airstream used to produce this sound.

Target

Feature Name Description
nsl nasal The air flows through the nose.
orl oral The air flows through the mouth.

Co-articulation

Feature Name Target
nzd nasalized nsl

Manner

Feature Name Description
occ occlusive The air flow is blocked within the vocal tract.
frv fricative The air flow is constricted, causing turbulence.
fla flap A single tap of the tongue against the secondary articulator.
tri trill A rapid vibration of the primary articulator against the secondary articulator.
app approximant The vocal tract is narrowed at the place of articulation without being turbulant.
vow vowel The phoneme is articulated as a vowel instead of a consonant.

Place of Articulation

The place of articulation is described in terms of an active articulator and one or more passive articulators[9]. The possible places of articulation are:

Place of Articulation Feature Active Lips Teeth Passive
bilabial blb lbl ulp
linguolabial lgl lmn ulp
labiodental lbd lbl utt
bilabial-labiodental bld bld ulp utt
interdental idt lmn utt
dental dnt apc utt
denti-alveolar dta lmn utt alf
alveolar alv lmn alf
apico-alveolar apa apc alf
palato-alveolar pla lmn alb
apical retroflex arf sac alb
retroflex rfx apc hpl
alveolo-palatal alp dsl alb
palatal pal dsl hpl
velar vel dsl spl
labio-velar lbv dsl ulp spl
uvular uvl dsl uvu
pharyngeal phr rdl prx
epiglotto-pharyngeal epp lyx prx
(ary-)epiglottal epg lyx egs
glottal glt lyx gts

Active Articulators

Feature Name Articulator
lbl labial lower lip
lmn laminal tongue blade
apc apical tongue tip
sac subapical underside of the tongue
dsl dorsal tongue body
rdl radical tongue root
lyx laryngeal larynx

Passive Articulators

Feature Articulator
ulp upper lip
utt upper teeth
alf alveolar ridge (front)
alb alveolar ridge (back)
hpl hard palate
spl soft palate (velum)
uvu uvular
prx pharynx
egs epiglottis
gts glottis

Co-articulation

Feature Name Articulator
pzd palatalized hpl
vzd velarized spl
fzd pharyngealized prx
nzd nasalized nsl
rzd rhoticized apc hpl

Phonation

The phonation features describe the degree to which the glottis (vocal chords) are open or closed.

Feature Name Description
vls voiceless The glottis is fully open, such that the vocal chords do not vibrate.
brv breathy voice The glottis is closed slightly, to produce a whispered or murmured sound.
slv slack voice The glottis is opened wider than mdv, but not enough to be brv.
mdv modal voice The glottis is opened to provide the optimal vibration of the vocal chords.
stv stiff voice The glottis is closed narrower than mdv, but not enough to be crv.
crv creaky voice The glottis is closed to produce a vocal or glottal fry.
glc glottal closure The glottis is fully closed.

Voice

Voice Feature Phoneme Model
voiceless vls vls
voiced vcd mdv

Vowel Height

Feature Name
hgh close (high)
smh near-close (semi-high)
umd close-mid (upper-mid)
mid mid
lmd open-mid (lower-mid)
sml near-open (semi-low)
low open (low)

Vowel Backness

Feature Name
fnt front
cnt center
bck back

Rounding and Labialization

Feature Name Rounded Position
unr unrounded No Close to the jaw.
ptr protruded Yes Protrude outward from the jaw.
cmp compressed Yes Close to the jaw.

The degree of rounding/labialization is specified using the following features:

Feature Name
mrd more rounded
lrd less rounded

Vowel Rounding

Rounding Feature Phoneme Model
unrounded unr unr
rounded rnd ptr if bck or cnt; cmp if fnt.

Syllabicity

Feature Name
syl syllabic
nsy non-syllabic

Consonant Release

Feature Name
frr fricative release
asp aspirated
nrs nasal release
lrs lateral release
unx no audible release (unexploded)

Tongue Root

The tongue root position can be specified using the following features:

Feature Symbol Name
atr ◌̘ advanced tongue root
rtr ◌̙ retracted tongue root

Fortis and Lenis

Feature Name
fts fortis
lns lenis

Stress

Feature Name
st1 primary stress
st2 secondary stress
st3 extra stress

Length

Feature Name
est extra short
hlg half-long
lng long

Rhythm

Feature Name
sbr syllable break
lnk linked (no break)

Intonation

Feature Name
fbr minor (foot) break
ibr major (intonation) break
glr global rise
glf global fall

Tone Stepping

Feature Name
ust upstep
dst downstep

Tones

Tones are defined using the following 3 properties:

tone_start  <value>
tone_middle <value>
tone_end    <value>

The <value> field for these properties is a number with one of the following values:

Tone <value>
extra high (top) 5
high 4
mid 3
low 2
extra low (bottom) 1

A level tone can be specified by just using the tone_start value. A raising or falling tone can be specified using the tone_start and tone_end values. A raising-falling (peaking) or falling-raising (dipping) tone can be specified using all three values.

References

  1. Kirshenbaum, Evan, Representing IPA phonetics in ASCII (HTML). 1993.

  2. Kirshenbaum, Evan, Representing IPA phonetics in ASCII (PDF). 2001.

  3. International Phonetic Association, The International Phonetic Alphabet and the IPA Chart. 2015. Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).

  4. Wikipedia. International Phonetic Alphabet. 2017. Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).

  5. Dunn, R. H., Cainteoir Text-to-Speech Phoneme Features. 2013-2015.

  6. Wikipedia. Voiced glottal fricative. 2017, Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).

  7. Wikipedia. Extensions to the International Phonetic Alphabet. 2017, Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).

  8. Wikipedia. Fortis and lenis. 2017, Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).

  9. Wikipedia. Place of articulation. 2017, Creative Commons Attribution-Sharealike 3.0 Unported License (CC-BY-SA).