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Afrikalinguistisches Kolloquium, 05. November 2013Humboldt-Universität zu BerlinSeminar für Afrikawissenschaften
Christfried Naumann
1. Introduction2. Research questions3. Procedure4. Examples5. First results
Vowels Vowels Vowels Vowels of of of of TaaTaaTaaTaa (West !(West !(West !(West !XoonXoonXoonXoon) ) ) ) and and and and their acoustic properties their acoustic properties their acoustic properties their acoustic properties
2
Introduction: Taa
"Khoisan"1. Hadza (isolate)
2. Sandawe (isolate)
3. Khoe-KwadiKwadi†Cape Khoekhoe†ǃOra-Xiri(†)Eini†Namibian Standard Khoekhoe
(Nama-Damara, Haiǁom, ǂAakhoe)
Shua (Cara, Deti†, ǀXaise, Danisi ...)Tshwa (Kua ...)Kxoe (Khwe, ǁAni ...; Ts'ixa ?)Gǁana (incl. Gǀui)Naro (Naro, Tsʼao ...)
4. Kxʼa(NW) ǃXunJuǀʼhoan (incl. ǂXʼao-ǁʼaen)ǂʼAmkoe (ǂHoan/Nǃaqriaxe, Sasi)
5. TuuTaa (West ǃXoon, East ǃXoon, ...)Lower Nossob† (ǀʼAuni, ǀHaasi, ...)Nǁng (Nǀuu = ǂKhomani, ...)ǀXam† (Strandberg, Achterveld, ...)ǁXegwi†
Hadza
Sandawe
ǂʼAmkoe
ǃXun
Juǀʼhoan
Kwadi†
Nama-Damara
Shua
TshwaNaro
Kxoe
Gǀui-Gǁana
Taa
LowerNossob†
Nǁng
ǀXam†
ǁXegwi†
Cape Khoekhoe†
ǃOra-Xiri(†)
Haiǁom
ǂAakhoe
Eini†
"San" Cf. Güldemann (in press).
HereroKgalagadi
Afrikaans
Introduction: Taa
Taa dialects
3
Introduction: Taa
Taa dialects
4
CentralKalahariGame Reserve
KgalagadiTransfrontierPark
NAMIBIA
BOTSWANA
SOUTHAFRICAca. 50 km
CC-BY Naumann 2012
Kumu
Takatswane
Okwa
Lone Tree
Dutlwe
Kokong
Lokalane
Baruchwe
Mabuasehube
Ohe
Phephane
Tsachas
Uichenas
Oorwinning
Bosduin
Hukuntsi
Khakhea
Tshane
Lotlhake
Makopong
Mabutsane
Goa
Aminuis
Ukwi
Kang
Ncaang
Zutshwa
Okomboha
Leonardville
Aranos
Okongowa
Otjikoto
Corridor 17Corridor 18
Corridor 15
Corridor 13Okonyoka
Kule
Ncojane
Ngwatle
MakeMonong
Hunhukwe
BereKacgae
Tsetseng
Maretswane
Inalegolo
Phuduhudu
Morwamasu
Tswane
Khekhenye
Kanaku
Kutuku
Kokhotsha
Werda
Lehututu
Ranyane
Tjaka/ Ben Hur
Metsimantle
Gunkas
GobabisMamuno/Charles Hill
Gochas
Sekoma
ǃAma
Tshaasi
East ǃXoon
ǂHuan
West ǃXoon
CentralKalahariGame Reserve
KgalagadiTransfrontierPark
NAMIBIA
BOTSWANA
SOUTHAFRICAca. 50 km
CC-BY Naumann 2012
CentralKalahariGame Reserve
KgalagadiTransfrontierPark
CentralKalahariGame Reserve
CentralKalahariGame Reserve
KgalagadiTransfrontierPark
NAMIBIA
BOTSWANA
SOUTHAFRICA
NAMIBIA
BOTSWANA
SOUTHAFRICAca. 50 kmca. 50 km
CC-BY Naumann 2012
Kumu
Takatswane
Okwa
Lone Tree
Dutlwe
Kokong
Lokalane
Baruchwe
Mabuasehube
Ohe
Phephane
Tsachas
Uichenas
Oorwinning
Bosduin
Hukuntsi
Khakhea
Tshane
Lotlhake
Makopong
Mabutsane
Kumu
Takatswane
Okwa
Lone Tree
Dutlwe
Kokong
Lokalane
Baruchwe
Mabuasehube
Ohe
Phephane
Tsachas
Uichenas
Oorwinning
Bosduin
Hukuntsi
Khakhea
Tshane
Lotlhake
Makopong
Mabutsane
Goa
Aminuis
Ukwi
Kang
Ncaang
Zutshwa
Okomboha
Leonardville
Aranos
Okongowa
Otjikoto
Corridor 17Corridor 18
Corridor 15
Corridor 13Okonyoka
Kule
Ncojane
Ngwatle
MakeMonong
Hunhukwe
BereKacgae
Tsetseng
Maretswane
Inalegolo
Phuduhudu
Morwamasu
Tswane
Khekhenye
Kanaku
Kutuku
Kokhotsha
Werda
Lehututu
Ranyane
Tjaka/ Ben Hur
Metsimantle
Gunkas
Goa
Aminuis
Ukwi
Kang
Ncaang
Zutshwa
Okomboha
Leonardville
Aranos
Okongowa
Otjikoto
Corridor 17Corridor 18
Corridor 15
Corridor 13Okonyoka
Kule
Ncojane
Ngwatle
MakeMonong
Hunhukwe
BereKacgae
Tsetseng
Maretswane
Inalegolo
Phuduhudu
Morwamasu
Tswane
Khekhenye
Kanaku
Kutuku
Kokhotsha
Werda
Lehututu
Ranyane
Tjaka/ Ben Hur
Metsimantle
GunkasAminuis
Ukwi
Kang
Ncaang
Zutshwa
Okomboha
Leonardville
Aranos
Okongowa
Otjikoto
Corridor 17Corridor 18
Corridor 15
Corridor 13Okonyoka
Kule
Ncojane
Ngwatle
MakeMonong
Hunhukwe
BereKacgae
Tsetseng
Maretswane
Inalegolo
Phuduhudu
Morwamasu
Tswane
Khekhenye
Kanaku
Kutuku
Kokhotsha
Werda
Lehututu
Ranyane
Tjaka/ Ben Hur
Metsimantle
Gunkas
GobabisMamuno/Charles Hill
Gochas
Sekoma
GobabisMamuno/Charles Hill
Gochas
Sekoma
ǃAma
Tshaasi
East ǃXoon
ǂHuan
West ǃXoon ǃAma
Tshaasi
East ǃXoon
ǂHuan
West ǃXoon
Introduction: Taa vowels
Front Back Restrictions
Close Mid Open Mid Closemodal, oral i e a o u
nasal ĩ <in> ã <an> ũ <un> V2
only
pharyngealised aˁ <aq> oˁ <oq> uˁ <uq> V1
only
tense ~ glottalised aˀ <a'> oˀ <o'> uˀ <u'> V1
only
breathy a ̤<ah> o̤ <oh> ṳ <uh> V1
only
strident a ̳<aqh> o̳ <oqh> u̳ <uqh> V1
only
(various combinations in diphtongs, including non-modal vowels in V1 and nasal vowels in V2, e.g. /u+i/, /u+ĩ/, /ṳ+i/, /ṳ+ĩ/, /o+e/, /o+a/, /o+ã/, /o̤+ã/, ...)
Lexical stems in native vocabulary:
C(C)V1CV
2
C(C)V1N
C(C)V1V25
Boden et al. (2008)
6
Vowels of Taa (West ǃXoon) Introduction: Taa vowels
Taa Ṽ, Vˁ, Vˀ, V̤, V̳
GǀuiṼ, Vˁ
Traill (1980), Fehn (p.c.), Gerlach (p.c.), Güldemann in Vossen (2013: 80), Haacke in Vossen (2013: 52ff.), Miller et al. (2009), Miller in Vossen (2013: 46ff.), Nakagawa (2006), Visser in Vossen (2013: 60), Vossen in Vossen (2013: 71).
ǂ'AmkoeṼ, Vˁ, Vˀ
Ts'ixaṼ
KhweṼ
Juǀ'hoanṼ, Vˁ("Vʢ"), Vˀ, V̤
NǁngṼ, Vˁ ("Vʢ")
KhoekhoeṼ
NaroṼ, Vˁ
Non-modal/non-oral
vowels in selected
Khoe, Kx'a and Tuu
languages
ShuaṼ
ǀXam†Ṽ, Vˁ, Vˀ ?
S.KuaṼ, Vˁ, V̳
ǃOraṼ
N.KuaṼ
7
Vowels of Taa (West ǃXoon)
1. Distinct acoustic properties (plotting vowels)
Time (s)12.05 12.40
5000
Fre
quen
cy (
Hz)
TWb130316-0110
0
1000
2000
3000
4000
5000
TWb130316-0110
Research questions
7
Vowels of American English (Peterson & Barney 1952)
Cf. broad band spectrogram (window 0.005s) of Taa /ʔaa/ "you" for one male speaker.
[ ʔ a: ḁ ]
Time (s)12.05 12.40
5000
Freq
uenc
y (H
z)
0
1000
2000
3000
4000
5000
Cf. narrow band spectrogram (window 0.02s).
8
Vowels of Taa (West ǃXoon) Research questions
1. Distinct acoustic properties (plotting vowels)
600
700
800
900
1000
1100
1200
1300
1400
-10 -5 0 5 10 15 20 25
FF FF1
1
1
1
(H
z)
(Hz)
(Hz)
(Hz)
HarmonicsHarmonicsHarmonicsHarmonics----totototo----noise rationoise rationoise rationoise ratio
<ah>
<aq>
<a>
<aqh>
Plot of F1 vs. harmonics-to-noise ratio of four phonation types for one female speaker of West !Xoon (Boden et al. 2008)
9
Vowels of Taa (West ǃXoon) Research questions
2. Simple underlying contrast /a, aˁ, aˀ, a,̤ a̳/ vs. /u, uˁ, uˀ, ṳ, u̳/ in V1? (Nakagawa 2010 for Gǀui)
>> /u/ vs. /o/ in V1 in Taa?
Nakagawa (2010: 31)
10
Vowels of Taa (West ǃXoon) Research questions
3. More research questions
• allophones & allophonic variation
• phonological representation of [i:], [e:], etc.
(/a+i/ ~ /i+i/ ?, /a+e/ ~ /e+e/ ?, etc.)
• consistent representation of [u] vs. [o] (e.g., for q__, !__ )
• further phonotactic restrictions (e.g., in diphtongs)
>> phonological questions for a concise description of West ǃXoon
11
Vowels of Taa (West ǃXoon) Procedure
Background
• phonological analysis
– structuralist linguistics: through minimal pairs (tea vs. pea, contrast in identical environments ) > sound categories (phonemes) by function (differentiation of meaning)
– (acoustic / articulatory data secondary)
• here: (hybrid categorical) usage-based approach (Pierrehumbert 2001, 2003, 2006)
– phonemes = sound categories with frequency distributions on the phonetic level to one abstract unit on the discrete phonological level
– > primary phonetic properties, secondary usage in sound systems
– equivalent to contrast in analogous environments ("no plausible statement of environmental conditioning") (cf. Burquest 2006: 35)
– distinct (non-overlapping) distributions (clusters) for comparable environments, e.g., F1 + F2 values for vowels #{t/th/d/s/z/l}___{t/th/d/s/z/l}#
Burquest (2006:35)
12
Vowels of Taa (West ǃXoon) Procedure
• March 2013: elicitation of words (in isolation)
• one female and two male speakers
• ca. 1500 ~ 750 vowels
• different contexts:
• C1__C(V) (C
1= anterior egressive or ʔ)
• C1 __ __ [CVV]
• ǀ__C(V), ǀ__ __
• ǃ__C(V), ǃ__ __
• Q__C(V), Q__ __ (Q - uvular egressive)
• CVC__
• annotation/labelling in PRAAT
• script-run measurements• duration
• F1, F2, F3 (at 1/8, 2/8 ... 7/8)
• shimmer, jitter, harmonics-to-noise ratio
• H1, H2, "A1"
• centre of gravity
• extraction of long-term average spectra ("LTAS", 1-1 and bandwidth = mean F0)
13
Vowels of Taa (West ǃXoon)
Modal vowel /a/ (/ʔaa/ "you.SG", anaphoric pronoun)
Time (s)10.52 110
5000
Freq
uenc
y (H
z)
TWb130316-0110
0
1000
2000
3000
4000
5000
TWb130316-0110
10.686
Examples
13
[ ʔ a: ḁ ]
Narrow band spectrogram (window 0.015s) of Taa /ʔaa/ "you" for one male speaker.
Frequency (Hz)0 5000
Sou
nd p
ress
ure
leve
l (dB/
Hz)
0
20
40
0 1000 2000 3000 4000 5000
-10
0
10
20
30
40
Spectral slice from 10.686 s +/- 20ms (= 1/4 of vowel length).
14
Vowels of Taa (West ǃXoon)
Nasal vowel /ã/ (/ʔaã/ "it", anaphoric pronoun, agreement class 2i)
Examples
14
[ ʔ ã: ḁ ]
Narrow band spectrogram (window 0.015s) of Taa /ʔaã/ "it" for one male speaker.
Spectral slice from 26.794 s +/- 20ms.
Time (s)26.46 27.050
5000
Freq
uenc
y (H
z)
TWb130316-0110
0
1000
2000
3000
4000
5000
TWb130316-0110
26.794 Frequency (Hz)0 5000
Sou
nd p
ress
ure
leve
l (dB/
Hz)
0
20
40
-10
0
10
20
30
40
0 1000 2000 3000 4000 5000
15
Vowels of Taa (West ǃXoon)
Time (s)62.96 63.580
5000
Freq
uenc
y (H
z)
TWb130316-0110
0
1000
2000
3000
4000
5000
TWb130316-0110
63.162
Pharyngealised vowel /aˁ/ (/aˁa/ "father")
Examples
15
[ aˁ a ḁ ]
Narrow band spectrogram (window 0.015s) of Taa /aˁa/ "father" for one male speaker.
Spectral slice from 63.162 s +/- 20ms (= 1/4 of vowel length).
Frequency (Hz)0 5000
Sou
nd p
ress
ure
leve
l (dB/
Hz)
0
20
40
-10
0
10
20
30
40
0 1000 2000 3000 4000 5000
16
Vowels of Taa (West ǃXoon)
Glottalised vowel /aˀ/ (/taˀa/ "you here")
Time (s)517.7 518.30
5000
Freq
uenc
y (H
z)
TWb130316-0110
0
1000
2000
3000
4000
5000
TWb130316-0110TWb130316-0110
517.945
Examples
16
[ t aˀ a ḁ ]
Narrow band spectrogram (window 0.015s) of Taa /taˀa/ "you here" for one male speaker. Formant contours in red, intensity contour in white.
Spectral slice from 517.945 s +/- 20ms (= 1/4 of vowel length).
Frequency (Hz)0 5000
Sou
nd p
ress
ure
leve
l (dB/
Hz)
0
20
40
-10
0
10
20
30
40
0 1000 2000 3000 4000 5000
17
Vowels of Taa (West ǃXoon)
Time (s)191.8 192.40
5000
Freq
uenc
y (H
z)
TWb130316-0110
0
1000
2000
3000
4000
5000
TWb130316-0110
192.033
TWb130316-0110
Breathy vowel /a/̤ (/taa̤/ "to refuse")
Examples
17
[ t a ̤ (a) ḁ ]
Narrow band spectrogram (window 0.015s) of Taa /taa̤/ "to refuse" for one male speaker. Formant contours in red, intensity contour in white.
Spectral slice from 192.033 s +/- 20ms (= 1/4 of vowel length).
Frequency (Hz)0 5000
Sou
nd p
ress
ure
leve
l (dB/
Hz)
0
20
40
-10
0
10
20
30
40
0 1000 2000 3000 4000 5000
18
Vowels of Taa (West ǃXoon)
Time (s)77.01 77.620
5000
Freq
uenc
y (H
z)
TWb130316-0110
0
1000
2000
3000
4000
5000
TWb130316-0110TWb130316-0110
77.218
Strident vowel /a̳/ (/a̳a/ "porridge")
Examples
18
[ ʔ a̳ a ḁ ]
Narrow band spectrogram (window 0.015s) of Taa /a̳a/ "porridge" for one male speaker. Formant contours in red, intensity contour in white.
Spectral slice from 77.218 s +/- 20ms (= 1/4 of vowel length).
Frequency (Hz)0 5000
Sou
nd p
ress
ure
leve
l (dB/
Hz)
-20
0
20
-20
-10
0
10
20
30
0 1000 2000 3000 4000 5000
19
Vowels of Taa (West ǃXoon) First results: Phonetic properties
19
100
200
300
400
500
600
700
800
900
1000
1100
4006008001000120014001600180020002200240026002800
F1
F2
Vowels in C__ __ context (with formant quality of V1 = V2): F1 vs. F2 for male speaker 278-FT
i
ih
i'
e
a
o
u
aqhaq
e'
ah
> 5 phonetic clustersby F1 x F2 > modal and non-modalphonations similar
20
Vowels of Taa (West ǃXoon) First results: Phonetic properties
Same procedure for a second speaker
200
300
400
500
600
700
800
900
1000
1100
1200
600800100012001400160018002000220024002600280030003200
F2
F1
Vowels in C__ __ context (with formant quality of V1 = V2): F1 vs. F2 for female speaker 276-JT
> similar contrasts> mid vowels more closed
21
Vowels of Taa (West ǃXoon) First results: Phonetic properties
> [i:], [e:], [a:], [o:], [u:], [ i̤:], ... in the context of C_ _#• complementary distribution (front vowel) monophtongs – diphtongs:
after coronal egressives, after uvular egressives,dental and palatal clicks bilabial, alveolar and lateral clicks(e.g., t__, s__, ǀ__, ǂ__, ...) (e.g., q__, χ__, ʘ__, ǃ__, ǁ__, ...)
[i:] ✓ −[ai] − ✓
[e:] ✓ −[ae] − ✓
aber:[a:] ✓ ✓
[o:] ✓ ✓[ao] ✓ ✓ ?
[u:] ✓ ✓[au] ✓ ✓
--> [i:], [ i̤:], [iʼ:], [e:], [e':]analysable as /ai/, /a̤/, /a'i/, /ae/, /a'e/(previously known)
22
Vowels of Taa (West ǃXoon) First results: Phonetic properties
22
-25
-20
-15
-10
-05
00
05
10
15
20
25
30
35
40
45
15 20 25 30 35 40 45 50 55 60
A1-
H1
H1
ah
a'
aq
aqh
a
--> good separation ofdifferent phonationqualities by H1 x A1-H1!
23
Vowels of Taa (West ǃXoon) First results: Phonetic properties
Vgl. Spektra:
Frequency (Hz)0 5000
Sou
nd p
ress
ure
leve
l (dB/
Hz)
0
20
40
0 1000 2000 3000 4000 5000
-10
0
10
20
30
40
[a:]
Frequency (Hz)0 5000
Soun
d pr
essu
re le
vel (
dB/
Hz)
0
20
40
-10
0
10
20
30
40
0 1000 2000 3000 4000 5000
[aˁ:]
Frequency (Hz)0 5000
Soun
d pr
essu
re le
vel (
dB/
Hz)
0
20
40
-10
0
10
20
30
40
0 1000 2000 3000 4000 5000
[aˀ:]
Frequency (Hz)0 5000
Soun
d pr
essu
re le
vel (
dB/
Hz)
0
20
40
-10
0
10
20
30
40
0 1000 2000 3000 4000 5000
[a̤:]
H1
H2
A1
24
Vowels of Taa (West ǃXoon) First results: Phonetic properties
A similar arrangement
30
35
40
45
50
55
60
65
70
25 30 35 40 45 50 55 60
H1 (dB)
S iz e of bubbles represents H2
A1
(d
B)
a
a'
ah
aq
aqh
Open vowels of different phonation qualities in C__ CV context (C1 – all consonants)for male speaker 278-FT
25
Vowels of Taa (West ǃXoon) First results: Phonetic properties
Vowels of different phonation qualities in C__ C(V)# contexts (C1 – all consonants) for male speaker 278-FT
Vowels in V1: H1 (dB ) (10th percentile - mean - 90th percentile)
48.3
45.3
51.3
50.4
47.4
53.5
44.2
37.6
49.748.9
43.1
53.7
50.1
45.5
53.8
36.9
31.6
43.1
40.7
36.9
44.3
39.1
33.5
43.4
47.6
43.9
51.051.7
48.7
54.0
53.0
51.5
54.7
34.6
29.8
39.3
30.8
22.5
39.0
30.4
21.3
36.5
34.8
31.8
37.8
36.0
32.4
41.6
38.0
34.9
42.5
20.0
25.0
30.0
35.0
40.0
45.0
50.0
55.0
60.0
a e i o u a' o' u' ah oh uh aq oq uq aqh oqh uqh
--> good separation of dif-ferent phonation qualities by H1 and related parameters across formant qualities
26
Vowels of Taa (West ǃXoon) First results: Contrast in Ccor
_C(V)
26
100
200
300
400
500
600
700
800
900
1000
1100
4006008001000120014001600180020002200240026002800
F1
F2
eo
u
aqaqh
uh
u'
Vowels in C__C(V) context (C1 = anterior egressive or glottal): F1 vs. F2 for male speaker 278-FT
i
a
note: •front vowels only in prefixes (si-), proper names and loans, such as Thenn-Thenn [name] or selfonn
27
Vowels of Taa (West ǃXoon) First results: [a] : [o] : [u] ? in Ccor
_C(V)
[a] : [o] : [u] in Ceggr.cor
__C# (male speaker 278-FT)
100
200
300
400
500
600
700
800
900
1000
1100
70080090010001100120013001400150016001700180019002000
F2
F1
a
o
u
tendency (native stems):• [o] _m• [u] _n
28
Vowels of Taa (West ǃXoon)
100
200
300
400
500
600
700
800
900
1000
1100
7008009001000110012001300140015001600170018001900200021002200
F2
F1
a(',h)
o(')
u(',h)
First results: [a] : [o] : [u] ? in Ccor
_C(V)
[a] : [o] : [u] in Ceggr.cor
__C# (female speaker 276-JT)
> partial neutralisation [u] ~ [o]?
29
Vowels of Taa (West ǃXoon) First results: [a] : [o] : [u] ? in Ccor
_C(V)
[a] : [o] : [u] in !__C(V)# (male speaker 278-FT)
> partial neutralisation [u] ~ [o]?
100
200
300
400
500
600
700
800
900
1000
1100
70080090010001100120013001400150016001700180019002000
F2
F1
30
Vowels of Taa (West ǃXoon)
100
200
300
400
500
600
700
800
900
1000
1100
70080090010001100120013001400150016001700180019002000
F2
F1
neutralisation u - o ?!
(u lowered, fine quality
depending on context)
First results: [a] : [o] : [u] ? in Ccor
_C(V)
[a] : [o] : [u] in !__C(V)# (female speaker 276-JT)
> partial neutralisation [u] ~ [o]!
31
Vowels of Taa (West ǃXoon) References
Acknowledgements to:
• Annika Vosseler (data preparation)
• Sven Grawunder (scripts)
Boden, Gertrud, Tom Güldemann, Roland Kießling & Christfried Naumann. 2008. The Phonological Units of Taa (West ǃXoon dialect). Poster presented at the Max Planck Institute for Evolutionary Anthropology. Leipzig.
Burquest, Donald A. 2006. Phonological Analysis – A Functional Approach. Third edition. Dallas (Texas): SIL.
Güldemann, Tom. In press. “Khoisan” linguistic classification today. In Tom Güldemann & Anne-Maria Fehn (eds.), Beyond “Khoisan”: Historical Relations in the Kalahari Basin. Amsterdam: Benjamins.
Miller, Amanda L., Johanna Brugman, Bonny Sands, Levi Namaseb, Mats Exter & Chris Collins. 2009. Differences in airstream and posterior place of articulation among N|uu clicks. Journal of the International Phonetic Association 39(2). 129–61. doi:10.1017/S0025100309003867.
Nakagawa, Hiroshi. 2006. Aspects of the Phonetic and Phonological Structure of the Gǀui Language. Johannesburg: University of the Witwatersrand PhD diss.
Nakagawa, Hirosi. 2010. Phonotactics of Disyllabic Lexical Morphemes in G|ui. Working Papers in Corpus-Based Linguistics and Language Education 5. 23–31.
Naumann, Christfried. Forthcoming. The Phoneme Inventory of Taa (West ǃXoon Dialect). In Rainer Vossen & Wilfrid H. G. Haacke (eds.), Essays in Memory of Anthony Traill. Cologne: Köppe.
Naumann, Christfried. In press. Towards a Genealogical Classification of Taa Dialects. In Tom Güldemann & Anne-Maria Fehn (eds.), Beyond “Khoisan”: Historical Relations in the Kalahari Basin. Amsterdam: Benjamins.
Peterson, Gordon E. & Harold L. Barney. 1952. Control Methods Used in a Study of the Vowels. Journal of the Acoustical Society of America24(2). 175–84.
Pierrehumbert, Janet B. 2001. "Exemplar Dynamics: Word frequency, Lenition and Contrast." In: Frequency Effects and the Emergence of Linguistic Structure , ed. by Joan Bybee and Paul Hopper, 137-57.
Pierrehumbert, Janet B. 2003. "Phonetic Diversity, Statistical Learning, and Acquisition of Phonology." In: Language and Speech (46/2-3), 115-54.
Pierrehumbert, Janet B. 2006. "The Next Toolkit." In: Journal of Phonetics (34), 516-30.
Traill, Anthony. 1980. Phonetic Diversity in the Khoisan Languages. In Jan W. Snyman (ed.), Bushman and Hottentot Linguistic Studies 1979, 167–89. Pretoria: University of South Africa.
Voßen, Rainer. 1997. Die Khoe-Sprachen. (Quellen Zur Khoisan-Forschung 12). Cologne: Köppe.
Vossen, Rainer (ed.). 2013. The Khoesan Languages. (Routledge Language Family Series). London: Routledge.
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