|Region||Amstetten, Lower Austria|
The Amstetten dialect is very unusual among the world's language varieties in that it can be analyzed as featuring five phonemic vowel heights. Phonetically speaking, the vowels typically transcribed with ⟨æ, ?, ?⟩ in IPA constitute a series of open-mid vowels ([?, oe, ?] in narrow transcription), one-third the distance between the open central /a/ and the close /i, y, u/ in the formant vowel space. The vowels transcribed with ⟨?, oe, ?⟩ and ⟨e, ø, o⟩ also differ from the cardinal vowels; the first series is close-mid ([e, ø, o] in narrow transcription), two-thirds the distance between /a/ and /i, y, u/. The remaining /e, ø, o/ are near-close ([e?, ø?, o?] in narrow transcription), a series of very high vowels that approach /i, y, u/ in their articulation. Among those, the back is somewhat more central than the neighboring and .
Amstetten vowels could be reclassified as follows, with redefined values of ⟨e, ø, o⟩ and ⟨?, oe, ?⟩:
The lowest of the rounded back vowels is known as dunkles a 'dark a' in Bavarian dialectology. This is why /a/ is not classified as a back vowel, as it is sometimes done in other languages in order to avoid positing a separate central category. It could, however, be classified as a front vowel, as the difference between central and front unrounded open vowels is based on height (with the open "front" vowel being more open), rather than backness in the formant vowel space, contrary to the official IPA chart.
Another language variety claimed to feature five phonemic vowel heights, the Weert dialect of Limburgish, spoken in the south of the Netherlands, contrasts five long front unrounded vowels /i:/, /e:/, /?:/, /æ:/ and /a:/. The close-mid /e:/ surfaces as a centering diphthong [e?], except before nasals. In the neighboring dialect of Hamont-Achel there are four degrees of openness, and the contast between /æ:/ and /a:/ is based purely on backness (front vs. central, both also contrast with the back /?:/). That is also highly unusual, and there is no other language variety that has been reported to contrast more than two open vowels based on backness alone.