Allophones of plosives

 

Allophones of plosives

Aspirated 

Voiceless plosives /p. t, k/ can be either aspirated or unaspirated depending on their phonetic environments. When /p/, /t/, and /k/ come at the beginning of a word or at the beginning of a stressed syllable, they are aspirated. That is, they are pronounced with a small puff of air. These are examples where /p, t, k/ are aspirated:

/p/ pan, price, appear, computer

/t/ top, table, potato, attend, attach,

/k/ can, kettle, accuse, Haiku

The IPA symbol for aspiration is a superscript [h]. In ‘potato,’ the p is aspirated because it is at the beginning of the word and the  ‘t’ is aspirated because it's at the beginning of a stressed syllable: /pʰəˈtʰeɪ.toʊ/.

Unaspirated

When voiceless plosives come in the middle or at the end of a word and when they do not begin a stressed syllable, they are not aspirated.  Also, when /p/, /t/, and /k/ are in a consonant cluster after /s/, they are unaspirated. There is no puff of air when we say them. 

/p/ span, spécial, spring

/t/ stop, stáple, string

/k/ scan, scátter, screen

Compare the pronunciation of the following words with and without aspiration:

pill  [pʰɪl]   spill  [spɪl]

till [tʰɪl] still [stɪl]

kill [kʰɪl] skill [skɪl]

held (unreleased)

When a plosive comes at the end of a word, it is often unreleased. It is optional whether we release the sound or not. To hold the sound, we start to say the sound by blocking off the air flow where the stop normally happens, but we don’t release the air. In the International Phonetic Alphabet, unreleased consonants are denoted with an upper-right corner symbol,  ̚ (e.g., [p̚]). The final plosives in these words can be pronounced in two ways: released (audible) or unreleased (inaudible)

released [p]: stop, hope, devélop

unreleased [p̚]: stop, hope, devélop

released [t]: coat, late, basket

unreleased [t̚]: coat, late, basket

released [k]: back, lake, stomach

unreleased [k̚]: back, lake, stomach

For example, in the sentence “This is my cat,” ‘cat’ can be pronounced either [kæt] or [kæt ̚]. 

Plosives are also unreleased when they are followed by another plosive or an affricate. For example, 

stacked, stopped, handbag

hot tea, black cat,  best part, big girl 

cold juice, lake church, that chair

Devoicing of voiced plosives

Devoicing of voiced plosives means that voiced plosives become voiceless.

When a pause follows after voiced plosives (/b, d, g/), they can  sound like their voiceless counterparts, (/p, t, k/). For example, “This is my lab, my bed, and my  bag” can sound like “This is my lap, my bet, and my back.” The way to distinguish between these two sentences is through the vowel length, since the vowel lengths are unaffected by the devoicing. So, the vowel length of words with originally voiced consonants is noticeably longer even though their final voiced consonants are devoiced.  So “This is my lab, my bed, and my  bag” will sound like “This is my la-ap, my be-et, and my ba-ack. This means that words ending in "voiced" and "voiceless" obstruents are still distinct, but they are not distinguished by voicing.