Gareth

Can also be pronounced as /ˈɡæɹ.ɪθ/ or /ˈɡæɹ.ɛθ/ in English
https://en.wiktionary.org/wiki/Gareth

The correct Welsh pronunciation of Gareth is GA RETH. There is no hesitation between the syllables and the R is not rolled as is common in American speech. GA is said like GAP. RETH can be said as RETH or R(UH)TH depending on where in Wales you come from - my experience is that the former is more likely in Welsh speaking regions or the old coal mining valleys and the latter is more likely in the mainly English speaking regions. I was born in Cardiff (the capital) and grew up in Barry (a small seaside town) - both English speaking.