Do loanwords have quasi-phonemic vowel reduction?


I've started to notice this, and I'm not sure whether my eyes are deceiving me
or not, but it seems as if several, but not all loans have a high statistical
probability of vowels being reduced/devoiced in contexts where they would be
very unlikely to in a native Japanese word, that place being fill-vowels being
introduced purely to fit with Japanese phonotactics.

As an example, in the loan “dórama” [accute accent used to indicate accented
mora] from English “drama”; the /o/ seems to be almost universally , somewhat,
devoiced by many speakers, which would be highly unlikely for an /o/ in
between two voiced sounds, in an accented mora in a native word.

I did a spectrographical analysis and it should be clear which of both
spectrograms is from “dórama” and which from “dóreka”, by the same speaker:

[![dórama vs. dóreka1](https://i.stack.imgur.com/iff2n.jpg)

Dark bands at the bottom indicate vowels or vowel-like sounds in spectrograms,
for those not in the know of this. It is clear that the dark band in the
bottom of the first mora in the first picture takes a far less prominent
existence than in the second one, indicating a reduction of vowel-like
qualities, as is common for Japanese reduced vowels — it should also be clear
that the /m/ in “dórama” has some vowel like qualities, whereas the /k/ in
“dóreka” does not.

I have used the speaker Skent from [this
list](https://forvo.com/word/%E3%83%89%E3%83%A9%E3%83%9E/#ja), which I also
used for “dóreka”, as he was conveniently in both. One may listen to all the
examples of “dórama” there and investigate whether one agrees with me that
the “do” mora is uncharacteristically reduced with all speakers, and compare
it with [these readings](https://forvo.com/word/%E3%81%A9%E3%82%8C/).

I could find no research that investigated this matter — do any Japanese
native speakers have any input on the matter whether they feel that not
reducing the “do” in “dórama” would sound unnatural or something else?

