1. Bird, S.: When marking tone reduces fluency: An orthography experiment in cameroon. Lang. Speech 42, 83–115 (1999)
2. Urua, E.-A.: The Tone system of Ibibio. In: Proceedings of Workshop on Typology of African Prosodic Systems (TAPS), Bielefeld University, Germany (2001)
3. Ekpenyong, M., Urua, E.-A., Watts, O., King, S., Yamagushi, J.: Statistical parametric speech synthesis for ibibio. Speech Commun. 56, 243–251 (2014)
4. Nida, E.A.: Practical limitations to a phonemic alphabet. In: Smalley, W. (ed.) Orthography Studies: Articles on New Writing Systems, pp. 22–30 (1964)
5. Baker, P., Bari, A., Dalby, D., Jatta, S., Mann, M., Saeed, J.: Writing African Languages: The Search for a Uniform Script. SOAS, UK (1982)