  This paper proposes an effective emotion control method for an end-to-end
text-to-speech (TTS) system. To flexibly control the distinct characteristic of
a target emotion category, it is essential to determine embedding vectors
representing the TTS input. We introduce an inter-to-intra emotional distance
ratio algorithm to the embedding vectors that can minimize the distance to the
target emotion category while maximizing its distance to the other emotion
categories. To further enhance the expressiveness of a target speech, we also
introduce an effective interpolation technique that enables the intensity of a
target emotion to be gradually changed to that of neutral speech. Subjective
evaluation results in terms of emotional expressiveness and controllability
show the superiority of the proposed algorithm to the conventional methods.
