  Recent text-to-speech models have reached the level of generating natural
speech similar to what humans say. But there still have limitations in terms of
expressiveness. The existing emotional speech synthesis models have shown
controllability using interpolated features with scaling parameters in
emotional latent space. However, the emotional latent space generated from the
existing models is difficult to control the continuous emotional intensity
because of the entanglement of features like emotions, speakers, etc. In this
paper, we propose a novel method to control the continuous intensity of
emotions using semi-supervised learning. The model learns emotions of
intermediate intensity using pseudo-labels generated from phoneme-level
sequences of speech information. An embedding space built from the proposed
model satisfies the uniform grid geometry with an emotional basis. The
experimental results showed that the proposed method was superior in
controllability and naturalness.
