Symbolic speaker adaptation with phone inventory expansion

This paper further develops a previously proposed adaptation method for speech recognition called symbolic speaker adaptation (SSA). The basic idea of SSA is to model a speaker\´s pronunciation as a blend of speech varieties (SVs) - regional dialects and foreign accents - for which the system has existing pronunciation models. The system determines during an adaptation process the relative applicability of those models, yielding a speech variety profile (SVP) for each speaker. Speaker-dependent lexica for recognition are determined from a speaker\´s SVP. In this paper, we discuss a series of experiments designed to analyze how the SSA method is affected by SV-balanced training, expanded phone inventories, reduced amounts of adaptation data, and speech from SVs not modeled by the system. The most dramatic improvements were obtained by using expanded ("SV-inclusive") phone inventories. SSA was also shown to be effective with a very small number of adaptation sentences. And, SSA\´s SV blending scheme yields higher accuracy than using a SV classification scheme for speakers of novel (unseen) SVs.