An ELT Glossary : Connected Speech - Sandhi Variations

Do you want one?

Uttered slowly and carefully, with every word said in isolation, the pronunciation of this sentence would be : 

/du: ju: wɒnt wʌn/

However, in connected speech - that is pronounced at normal speed in conversation - various changes would occur to the pronunciation in order to make the words easier to say rapidly.

These changes - known as sandhi variations - include assimilation, consonant lenition,  C-V catenation,  elision, epenthesis, gemination, vowel reduction,  V-V liaison, and yod coalescence. Click on the links for a detailed explanation of each.

The changes that occur often have a "knock-on" effect - that is, a small initial change causes another - and sometimes yet another so that the final utterance may be quite different from the citation form of the words.

This can be seen in the sentence cited above. What might happen there?

First of all, Do and you, being  unstressed grammatical words, would be likely to be affected by vowel reduction, in both cases the /u:/ changing to the schwa /ə/  : /də jə/. However, with only the weak vowel between them, the /d/ and /j/ sounds would be likely to blend into an affricate (yod coalescence), eliding the first /ə/ completely : /ʤə/.

want one might show a similar chain of changes. There might very well be a change to the /t/ first of all so that it was either elided completely - /wɒn wʌn/  or replaced with a glottal stop (consonant lenition) :  /wɒnʔ wʌn/

In the case that /t/ is elided completely, this will leave  an alveolar nasal consonant (/n/) next to a bilabial sound (/w/). To make the transition easier, the /n/ may be assimilated to the bilabial nasal /m/ (regressive assimilation of place). However, as this means that the lips must first be closed to allow air to pass out of the nose before being partially reopened to form /w/, the result would be a sudden release of the air remaining in the mouth - and therefore the production of an epethentic bilabial plosive /p/ :  /wɒmp wʌn/

This means that our original /du: ju: wɒnt wʌn/ could potentially become /ʤə wɒmp wʌn/.

Notice that these changes are only possibilities. Some are more likely than others, but in many cases it's a matter of "either this or that". Whether they are used and which is used will depend on both the situation and the speaker. In some situations we may naturally speak more slowly and carefully than in others - when giving a speech as opposed to conversational chat for example. and individual speakers will not only speak at different rates naturally, but will also have different accents , which may affect the changes made or not made.  A higher rate of consonant lenition involving  /t/  becoming  [ʔ]  might be expected in London English, for instance than in some other varieties of British English. This means that the final realisation of our example sentence could be any of the following, or indeed or any other combination of the features  
/ʤu: wɒn wʌn/  /ʤə wɒnʔ wʌn/  /də ju: wɒmp wʌn/ etc