Typically, the comparison is made with a default, unmarked articulation of the same phoneme in a neutral sound environment.
The relative position of a sound may be described as advanced (fronted), retracted (backed), raised, lowered, centralized, or mid-centralized.
In verbal description, the prefix pre- may be used to indicate fronting, especially in the terms prepalatal and prevelar.
In most dialects of English, the back vowel /u/ is farther forward than what is normally indicated by the IPA letter ‹u›.
In English, the plosive in the affricate /tʃ/, as in the word church, is farther back than an alveolar /t/ due to assimilation with the postalveolar fricative /ʃ/.
In English, the /d/ in the phrase "I need that" is farther front than normal due to assimilation with the interdental consonant /ð/, and may be transcribed as [aɪ̯ ˈniːd̟ ðæt].
Officially, the IPA symbol [a] stands for the open front unrounded vowel.
This may be partially due to the fact there is only a dedicated IPA symbol for one of them, the velar approximant.
In addition, many of the points along the series may be nasalized or lateralized as well, and these parameters are independent of stricture.
Before the letters [ɘ, ɵ, ɜ, ɞ] were added to the IPA in 1993, the symbols [ë, ö, ɛ̈, ɔ̈] were used for these near-schwa values.
[ë, ö, ɛ̈, ɔ̈] would now be assumed to represent articulations intermediate between [e, o, ɛ, ɔ] and [ɘ, ɵ, ɜ, ɞ].
Similarly, [ï, ÿ, ü, ɯ̈] would be intermediate between [i, y, u, ɯ] and [ɨ, ʉ].
The transcription [ɥ̈] vs. [ẅ] may also denote a distinction in the type of rounding, with the former symbol denoting a semivowel with compressed rounding typical of front vowels, and the latter symbol denoting a semivowel with protruded rounding typical of central and back vowels, though an additional verbal clarification is usual in such cases, as the IPA does not provide any official means to distinguish sounds with compressed and protruded rounding.
That is, they are closer to the mid-central vowel schwa [ə] not just by means of centralization, but also by raising or lowering.
An example from Polish is zobaczyłem dziś dwa samochody [zɔ̽bɐˈt͡ʂɘwɛ̽m ˈd͡ʑɪʑ ˈdvɐ sɐmɔ̽ˈxɔ̽dɘ] ('I saw two cars today'), instead of the standard [zɔbäˈt͡ʂɘwɛm ˈd͡ʑiʑ ˈdvä sämɔˈxɔdɘ].
[4] The Extensions to the IPA have two additional symbols for degrees of rounding: spread, as in [i͍], and open-rounded ⟨ꟹ⟩ (œ), as in English [ʃœ] and [ʒœ].
Many sound changes involve changes in place of articulation: Symbols to the right in a cell are voiced, to the left are voiceless.