There are five vowels in Slovene: a, e, i, o, u. The letter r in some Slovene words replaces the vowel when it stands before a consonant, as in rdeč (red) or rjav (brown), or when it stands between two consonants, as in Brnik (the Ljubljana airport) or in vrt (garden). The sound of each vowel is pure and very clear.
a
the 'u' in "mum"