hmm... don't know what letter combo will get this sound across, but i pronounce "a-vi-synth", with the "a" sound said like @ or "cat" (without the consonants of course). i've picked the closest one above... great poll idea... somebody must've been bored ;)
I only pronounce it in dutch sentences (never actually talk to any foreigners about it), so for me it's ah-vee-synth (synth being the normal english pronounciation). In english I'd say ay-vee-synth though.
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If I should pronounce it to someone from my own country, it sounds a lot like option 2. If I'd pronounce it to a foreigner, it'd probably sound like option 1. The difference is lies in a softer 'v' (wee) sound in my native language. OTOH, german 'v' is a lot more like 'f', so they might also have another pronounciation.