I study in Berlin and I've noticed that long vowels preceding an R have a very different quality. In specific, they are consistently more open, sometimes mixing with their "short vowel" equivalent. For example, the starting vowel of the diphthongs in:
Wer ([ve̞ɐ] or even [vɛɐ]), der (de̞ɐ, can go as low as [dɐ]!), Leer
doesn't sound at all like the vowel in
Tee [tʰe:], Bete [be:tə]
Same can be said for the other vowels, but "e" and "o" seem to be affected the most.
Is this considered standard German? Has anyone written anything about it (I love reading books about phonology/phonetics) Here is a 4 seconds recording of Helmut Krauss on Audible: https://drive.google.com/open?id=14oobrQXIRCIQmyv4GnR7MNj0wQyRB4zJ
In Northern Germany, the R is pronounced as a gliding ɐ even after short vowels. Can we say that in Northern Germany there is no contrast between short and long vowels before R?