J. Yamagishi, M. Tamura, T. Masuko, K. Tokuda, T. Kobayashi,
A Training Method of Average Voice Model for HMM-based Speech Synthesis,”
IEICE Trans. Fundamentals of Electronics, Communications and Computer Sciences, E86-A, no.8, pp.1956-1963, August 2003.
(See paper on IEICE web site)

J. Yamagishi, M. Tamura, T. Masuko, K. Tokuda, T. Kobayashi,
A Context Clustering Technique for Average Voice Models,”
IEICE Trans. Information and Systems,
E86-D, no.3, pp.534-542, March 2003
(See paper on IEICE web site)