Intervocalic alveolar flapping

Intervocalic alveolar flapping is a phonological process found in many dialects of English, especially North American English and Australian English, by which either or both prevocalic (preceding a vowel) /t/ and /d/ surface as the alveolar tap [ɾ] after sonorants other than /ŋ/, /m/, and (in some environments) /l/.

• after vowel: butter
• after r: barter
• after l: faculty (but not immediately post-tonic: alter → al[tʰ]er, not *al[ɾ]er)

Homophonous pairs 

In many accents, such words as riding and writing continue to be distinguished by the preceding vowel: though the consonant distinction is neutralized, the underlying voice distinction continues to select the allophone of the /aɪ/ phoneme preceding it. Thus for many North Americans, riding is [ɹaɪɾɪŋ]^{[citation needed]} while writing is [ɹɐɪɾɪŋ].^{[citation needed]} Vowel duration may also be different, with a longer vowel before tap realisations of /d/ than before tap realisations of /t/. At the phonetic level, the contrast between /t/ and /d/ may be maintained by these non-local cues, though as the cues are quite subtle, they may not be acquired/perceived by others. A merger of /t, d/ can then be said to have occurred.^{[citation needed]}
The cluster [nt] can also be flapped/tapped; the IPA symbol for a nasal tap is [ɾ̃]. As a result, in quick speech, words like winner and winter can become homophonous. Flapping/tapping does not occur for most speakers in words like 'carpenter' and 'ninety', which instead surface with [d].^[2]
A similar process also occurs in other languages, such as Western Apache (and other Southern Athabaskan languages). In Western Apache, intervocalic /t/ similarly is realized as [ɾ] in intervocalic position. This process occurs even over word boundaries. However, tapping is blocked when /t/ is the initial consonant of a stem (in other words tapping occurs only when /t/ is stem-internal or in a prefix). Unlike English, tapping is not affected by suprasegmentals (in other words stress or tone).


Homophonous pairs 

/-t-, -nt-/	/-d-, -n-/	Relevant rhyme	Notes
atom	Adam	/ˈæɾəm/
batter	badder	/ˈbæɾə(ɹ)/
banter	banner	/ˈbæɾ̃ə(ɹ)/
beating	beading	/ˈbiːɾɪŋ/
betting	bedding	/ˈbɛɾɪŋ/
bitter	bidder	/ˈbɪɾə(ɹ)/
boating	boding	/ˈboʊɾɪŋ, ˈboːɾɪŋ/
butting	budding	/ˈbʌɾɪŋ/
catty	caddy	/ˈkæɾi/
center	sinner	/ˈsɪɾ̃ə(ɹ)/	With pen-pin merger.
cited	sided	/ˈsaɪɾɪd/
coating	coding	/ˈkoʊɾɪŋ, ˈkoːɾɪŋ/
cuttle	cuddle	/ˈkʌɾəl/
debtor	deader	/ˈdɛɾə(ɹ)/
futile	feudal	/ˈfjuːɾəl, ˈf(j)ɪuːɾəl/
greater	grader	/ˈɡɾeɪɾə(ɹ), ˈɡɾeːɾə(ɹ)/
hearty	hardy	/ˈhɑː(ɹ)ɾi/
heated	heeded	/ˈhiːɾɪd/
hurting	herding	/ˈhɜː(ɹ)ɾɪŋ/
inter-	inner	/ˈɪɾ̃ə(ɹ)/
jointing	joining	/ˈdʒɔɪɾ̃ɪŋ/
kitty	kiddie	/ˈkɪɾi/
ladder	latter	/ˈlæɾə(ɹ)/
liter	leader	/ˈliːɾə(ɹ)/
manta	manna	/ˈmæɾ̃ə/
matter	madder	/ˈmæɾə(ɹ)/
meant it	minute	/ˈmɪɾ̃ɪt/	With pen-pin merger.
metal	medal	/ˈmɛɾəl/
metal	meddle	/ˈmɛɾəl/
mettle	medal	/ˈmɛɾəl/
mettle	meddle	/ˈmɛɾəl/
minty	many	/ˈmɪɾ̃i/	With pen-pin merger.
minty	mini	/ˈmɪɾ̃i/
minty	Minnie	/ˈmɪɾ̃i/
neuter	nuder	/ˈn(j)uːɾə(ɹ), ˈn(j)ɪuɾə(ɹ)/
otter	odder	/ˈɒɾə(ɹ)/
painting	paining	/ˈpeɪɾ̃ɪŋ/
patty	paddy	/ˈpæɾi/
petal	pedal	/ˈpɛɾəl/
petal	peddle	/ˈpɛɾəl/
pettle	pedal	/ˈpɛɾəl/
pettle	peddle	/ˈpɛɾəl/
planter	planner	/ˈplæɾ̃ə(ɹ)/
potted	podded	/ˈpɒɾɪd/
rated	raided	/ˈɹeɪɾɪd/
righting	riding	/ˈraɪɾɪŋ/
router	ruder	/ˈɹuːɾə(ɹ)/
Saturday	sadder day	/ˈsæɾə(ɹ)deɪ/
seating	seeding	/ˈsiːɾɪŋ/
sent it	senate	/ˈsɛɾ̃ɪt/
set it	said it	/ˈsɛɾɪt/
shutter	shudder	/ˈʃʌɾə(ɹ)/
sighted	sided	/ˈsaɪɾɪd/
sited	sided	/ˈsaɪɾɪd/
title	tidal	/ˈtaɪɾəl/
traitor	trader	/ˈtreɪɾə(ɹ)/
Tudor	tutor	/ˈt(j)uːɾə(ɹ), ˈt(j)ɪuɾə(ɹ)/
waiter	wader	/ˈweɪɾə(ɹ)/
wetting	wedding	/ˈwɛɾɪŋ/
winter	winner	/ˈwɪɾ̃ə(ɹ)/
whiter	wider	/ˈwaɪɾə(ɹ)/	With wine-whine merger.
writing	riding	/ˈraɪɾɪŋ/

1. Sara Went Shopping 

Sara Smith, a Pasadena resident, went shopping. She is thirty, and has lived at thirty thirty-seven North Foothill Street since nineteen ninety-two. Sara has been married to John for seven years. They have two children; Bob is five years old and Nancy is three. Sara owns a nineteen ninety-five four-door blue Toyota. At nine a.m., Sara got into her car and drove to Barget, a department store a mile away.

Barget was having a holiday sale. Sara bought a four-slice toaster for twenty-nine ninety-five plus tax. The regular price was thirty-five ninety-five. She paid by check. On her way home, Sara stopped at MilkPlus to buy a gallon of nonfat milk. The milk was three dollars fifty cents. Sara got fifty cents back in change.

Sara arrived home at ten a.m. John and the kids were still sleeping. She woke them up and then made a hot and nutritious breakfast for everyone. 

http://www.rong-chang.com/qa2/stories/story001.htm

2. Man Injured at Fast Food Place

A seventy-nine-year-old man was slightly injured on Saturday while waiting in his brand new convertible in a drive-through lane at Burger Prince restaurant. Herman Sherman of Northville suffered a mild burn about nine p.m. when a young female employee accidentally spilled a cup of coffee into his lap. Sherman said the coffee was hot but not scalding.

He refused medical aid, saying the only problem was the stain on his slacks, but it would wash out. He was given a fresh refill. Before Sherman drove off, the restaurant manager, John Johnson, gave him two free gift certificates--one for an extra-large coffee and one for the restaurant's newest sandwich, the McRap.

The employee, who was a new hire, was let go later that evening. She was quite upset. She said she would probably sue Burger Prince for letting her go. She said it was the man's fault for ordering something that she might be able to spill.

http://www.rong-chang.com/qa2/stories/story002.htm