I haven’t read all the above posts, but here’s my take on the question. β and δ are both voiced stops, labial and coronal respectively, so phonetically they’re very close. Phonologically the combination is comparable with πτ just as Hylander said. βδ (and πτ) will not have been pronounced simultaneously but successively (without intervening release) as the tongue was brought into play; the δ is plosive, marking the release and leading directly into the vowel.
To a native English speaker the sound of word-initial βδ is scarcely distinguishable from δ (or τ in the case of πτ—and I find the δ/τ tends to be aspirated), but crucially it begins with the lips closed; it behaves prosodically as any other two-consonant cluster. Of course we can’t go by the modern pronunciation.
PS. Hylander’s latest disposes of any practical difficulty. I don’t know Russian.
βδ (and πτ) will not have been pronounced simultaneously but successively (without intervening release) as the tongue was brought into play; the δ is plosive, marking the release and leading directly into the vowel.
I believe this is what was meant by “simultaneous pronunciation” - that is, without the release between /b/ and /d/. When I compare with “Bob Dylan” or pronounce as you describe, yes, I don’t find it that hard to pronounce the cluster and no /ə/ can occur.
Another way for me to explain how to pronounce word initial/absolute onset /(bd)/ is to do /md/ initially to check tongue and lip articulation, but then not allowing the air to flow through the nose while maintaining same articulation for tongue and lip. Would you agree on that?
When you say
it behaves prosodically as any other two-consonant cluster
are you referring to metric or other prosodic behaviours?
There is also the practical joke that goes, “M-A-C-D-O-N-A-L-D is pronounced MacDonald and M-A-C-B-R-I-D-E is pronounced MacBride, how is M-A-C-H-I-N-E-S pronounced?” (machines - MacHines) Or "If we add an “e” to the front of “book”, we get “ebook” as in electronic book, an “e” to the front of “mail” we get “email” (electronic mail), so what do we get when we add an “e” to the front of “yes”? (eyes - ee-yes as in electronic yess, is the expected incorrect response).
I don’t think the Bob Dylan analogy holds. The syllable boundary falls between the two words. English and Greek are phonemically distinct, and #βδ is simply not a sound we have in English. In Greek it’s an ugly one, and I imagine always onomatopoeic, as it certainly is in βδέω fart. (So if it doesn’t sound like a fart you’re not pronouncing it correctly?) Similarly with πτ-, as in πτύω spit (but not πτερ- “wing” words, where πτ represents a collapsed πετ, cf. Russian #bd.)