I started learning Irish and I wanted to understand velarisation in Irish.
Palatilisation and velarisation often assimilate sounds next to them to produce new sounds
“edge” comes from Proto Germanic agjō. Over time the /g/ got palatilised and the /jo/ was lost. Palatilisation produces /egʲ/ (and /a/ becomes /e/, seen in “angle-land” becoming “england”)
/dʒ/ is easier to say so /gʲ/ became /dʒ/
The same happened in Irish. Back vowels pulled the tongue backwards so /fa/ became /fˠa/
But sounds don’t like to stick around so they assimilate which means the sounds in the word change to make the pronunciation more smooth so /fˠa/ became /fɰa/. /ɰ/ is a /w/ without rounding your lips. /g/ and /w/ are both velar sounds. /g/ is a velar stop where the throat closes and then opens to release air. /ɰ/ is basically a un-stopped /g/
Later on the /a/ sound shifted to an /i/ so we have /fˠi/. We know it must have been a back vowel before because otherwise the f wouldn’t be velarised. So “faoi” is written like that to indicate velarisation, and its IPA transcription is /fˠiː/ which has long since just become assimilated to /fɰi/ which sounds a bit like /fwi/
I like looking in depth at parts of language so that I can get to grips with what is actually happening and it allows me to notice things that I haven’t noticed before.