Voiced sounds were simulated with a computer model of the vocal fold composed of a single mass vibrating both parallel and perpendicular to the airflow. The major improvement of the present model over the twomass model is that it has a wider continuous frequency range where self-excitation is possible both below and above the first formant frequency of the vocal tract. The two-dimensional model can therefore successfully be applied to the sound synthesis of a high-pitched soprano singing, where the fundamental frequency sometimes exceeds the first formant frequency.