An Introduction to French Pronunciation

126 Consonantal Assimilation
Note that in the middle of words in which b precedes /t/
or /s/, the pronunciation with a voiceless fortis, i.e. /p/, is
normal, e.g. obtenir /bptcni:r/, subtil /syptil/, absent /apse/,
absolu /apsbly/, abstrait /apstrε/, absurde /apsyrd/, obscur
/bpsky:r/, observer /bpsεrve/, obstiné /bpstine/.
18.2.5 Assimilation of a voiceless consonant to a following
voiced consonant also occurs, though much less widely than
the regressive assimilation of voiced consonants discussed
in 18.2.4. This type of assimilation often affects the first
consonant only to the extent of producing a voiced fortis,
indicated by a subscript [ ˇ ], e.g. (la) coupe de France [ku7 dc
fre:s], dites donc! [di5 df], vingt-deux [vh5dø] (note that vingt
+ a numeral is pronounced /vht/ not /vh/, e.g. vingt-cinq
/vhtsh:k/), chaque jour [ʃa3 ʒu:r], avec moi [avε3 mwa], deux
secondes [dø 4gf:d] (note that, despite the spelling, second,
seconde are pronounced /scgf, scgf:d/), une tasse de café
[yn ta4 dc kafe].
Assimilation may, however, be taken to the extent of
producing a normal voiced lenis, e.g. vingt-deux /vhddø/ (with
a geminate consonant), deux secondes /dø zgf:d/. A voiced
lenis is usual in the word anecdote /anεgdbt/, but otherwise
this type of assimilation may safely be ignored by foreigners.
18.3 Progressive Assimilation
18.3.1 Progressive assimilation is relatively uncommon in
French (as in English, see 18.1.4). It occurs in particular in the
following contexts:
18.3.2 A voiceless [t] occurs after /s/ as in asthme [ast],
communisme [kbmynist], or /t/, rythme [ritt] (see 16.6).
18.3.3 A voiceless allophone of /v/, viz. /x/ (or sometimes
the corresponding voiceless phoneme /f/) can occur after /ʃ/,
as in ce cheval [sc ʃxal], les cheveux [le ʃxø].