Assimilation of place of articulation

Assimilation of place of articulation is most clearly observable in some cases where a final consonant with alveolar place of articulation is followed by an initial consonant with a place of articulation that is not alveolar.

1. [ t ] → [ p ] when [ t ] precedes [ p m b ]
– right place [raɪt pleɪs] –>> [ raɪp pleɪs ]
– white bird [waɪt bɜːd] –>> [ waɪp bɜːd ]
– that person [ðæt ˈpɜːsn]–>>[ðæp pɜːsn]
– light blue [laɪt bluː] –>>[ laɪp bluː ]
– meat pie [miːt paɪ]–>>[ miːp paɪ ]
– not me [nɒt miː]–>>[ nɔp miː ]
2. [ d ] → [ b ] when [ d ] precedes [ p m b ]
– hard path [hɑːd pɑːθ]–>>[ hɑːb pɑːθ ]
– good boy [gʊd bɔɪ]–>>[gʊb bɔɪ ]
– good morning [gʊd ˈmɔːnɪŋ]–>>[gʊb mɔːnɪŋ ]
– good man [gʊd mæn]–>>[gʊb mæn ]
3. [ n ] → [ m ] when it precedes [ p m b ]
– gone past [gɒn pɑːst] –>>[gɒm pɑːst ]
– gone back [gɒn bæk] –>>[gɒm bæk ]
– ten men [tɛn mɛn]–>>[ tɛm mɛn ]
4. [ t ] → [ k ] when it precedes [ k g ]
– white coat [waɪt kəʊt]–>>[ waɪk kəʊt ]
– that case [ðæt keɪs]–>>[ðæk keɪs]
– bright color [braɪt ˈkʌlə]–>>[ braɪk kʌlə ]
– quite good [kwaɪt gʊd]–>>[ kwaɪk guːd ]
5. [ d ] → [g ] when it precedes [ k g ]
– bad cold [bæd kəʊld]–>>[ bæg kəʊld ]
– good girl [gʊd gɜːl]–>>[ gʊg gɜːl ]
– red gate [rɛd geɪt]–>>[ rɛg geɪt ]
6. [n] → [ŋ ] when it precedes [ k g ]
– one cup [wʌn kʌp]–>>[ wʌŋ kʌp ]
– main gate [meɪn geɪt]–>>[ meɪŋ geɪt ]
7. Similarity the sequences [ n ] and [ nd ] may be replaced by [ mp ] or [ŋk] and [ mb] or [ŋg]
Examples:
– Plant port [ plɑːmp pɔt ]
– Stand back [ stæmb bæk ]
– Plant carrot [ plɑːŋk kærət ]
– Stand guard [ stæŋg gɑːd]
Event the sequence [ dnt ] and [ tnd ]
– couldn’t come [ kʊgŋk kʌm ]
– couldn’t be [ kʊbmp biː ]

However, the same is not true of the other alveolar consonants [ s and z ] behave differently, the only noticeable change being that:[ s ] become ʃ and becomes and z becomes ʒ when followed by ʃ or j
Examples:
[ s ] → [ʃ ] when it precedes [ʃ or j ]
– this shoe [ðɪʃ ʃuː ]
– this year [ðɪʃ jɪə ]
[ z ] → [ʒ ] when it precedes [ʃ or j ]
– those shops [ðəʊʒ ʃɔps ]
– where’s your [ wɛəʒ jɔːz ]

None of these alteration necessary so although you will hear English people use them, especially when they spoken quickly, you need not imitate them./