The Unaccented Vowels - from Nielsen

"The introduction of a stress accent in Proto-Germanic and its
fixation on the initial syllable of the word (van Coetsem 1994:52-4)
had a decisive effect on the subsequent development of Germanic in
that the segments of the unaccented syllables were frequently
reduced or lost (e.g. through syncope or apocope) and that
assimilatory phenomena such as umlaut and breaking (fracture) of
accented vowals went hand in hand with vocalic reduction in the
unaccented syllables.
Another important consequence of the accent modification was that
Germanic could no more uphold just short and long monophthongal
subsystems, but had to operate with accented and unaccented
parameters as well. The unaccented vowel systems of the earliest
attested languages in North-Western Europe will be discussed and
compared below.
Let us here illustrate the level of reduction and loss in the
early Germanic dialects by translating the Early Runic legend on the
famous Gallehus gold horn from ca. AD 400 into the other attested
languages and, for comparison, into Proto-Germanic (cf. Antonsen
1986:322-4):

ek hlewagastiz holtijaz horna tawido
I, Hlewagastiz of holt, made the horn.

The Proto-Germanic equivalent would be:

ek hlewagastiz hultijaz hurnan tawiðôn

It will be noted that the number of syllables (13) in the
Gallehus inscription corresponds exactly to that of Proto-Germanic.
But Early Runic is not identical with Proto-Germanic as the loss of
the final nasals in "horna" and "tawido" clearly shows. For the
shift of accented U into O in "holtijaz" and "horna", see below.

The only other attested Germanic language roughly contemporary
with Early Runic is Gothic, the chief linguistic monument in which
is Wulfila´s translation of the Bible from the latter half of the
fourth century AD at a time when the Visigoths lived in the eastern
Balkans. Translated into Gothic the Gallehus inscription would look
like this:

ik hliugasts hulteis haúrn tawida

The three intermediate words have been considerably shortened,
the whole text having been reduced from 13 to 9 syllables in
comparison with Proto-Germanic. And the long vowel in the final
syllable of the last word has been shortened to -A. The level of
reduction in the Gothic demonstrates that this dialect has clearly
branched off from the contemporaneous Germanic idiom spoken in
Northern Europe as represented by Early Runic, cf. van Coetsem
1994:183-4 and Seebold 1994:87.
Although attested much later, the remaining Germanic dialects
also exhibit 9 syllables as evidenced by our reconstruction of the
Gallehus in the early North and West Germanic languages:

Old Norse: ek hlégestr hyltir horn görða (táða) (my note: Danish Ö)

Old English: ic hlêogiest hylte horn tâwode

Old Frisian: ik hlî-iest helte horn tâwade

Old Saxon: ik hleogast hulti horn tôida

Old High German: ih (hleo)gast hulzi horn zawita

Unlike Gothic, in which the Gmc. nsm. case-suffix -Z had become
devoiced (-S), the Old Norse has rhotacised the ending to -R, while
the West Gmc. languages show no trace of any nsm. case-marker. Old
Norse, Old English and Old Frisian have I-mutated vowels in -gestr,
-giest, -iest nad hyltir, hylte, helte."

Regards,
Konrad.