  We propose an end-to-end speech synthesizer, Fast DCTTS, that synthesizes
speech in real time on a single CPU thread. The proposed model is composed of a
carefully-tuned lightweight network designed by applying multiple network
reduction and fidelity improvement techniques. In addition, we propose a novel
group highway activation that can compromise between computational efficiency
and the regularization effect of the gating mechanism. As well, we introduce a
new metric called Elastic mel-cepstral distortion (EMCD) to measure the
fidelity of the output mel-spectrogram. In experiments, we analyze the effect
of the acceleration techniques on speed and speech quality. Compared with the
baseline model, the proposed model exhibits improved MOS from 2.62 to 2.74 with
only 1.76% computation and 2.75% parameters. The speed on a single CPU thread
was improved by 7.45 times, which is fast enough to produce mel-spectrogram in
real time without GPU.
