in X-SAMPA,  is used for the open front unrounded vowel and  is used for the open back unrounded vowel.
ɪn ˈɛkssˈæmpə,  ɪz jˈuːzd fɚðɪ ˈoʊpən fɹˈʌnt ʌnɹˈaʊndᵻd vˈaʊəl ænd ɪz jˈuːzd fɚðɪ ˈoʊpən bˈæk ʌnɹˈaʊndᵻd vˈaʊəl.