  Recently it was shown that within the Silent Speech Interface (SSI) field,
the prediction of F0 is possible from Ultrasound Tongue Images (UTI) as the
articulatory input, using Deep Neural Networks for articulatory-to-acoustic
mapping. Moreover, text-to-speech synthesizers were shown to produce higher
quality speech when using a continuous pitch estimate, which takes non-zero
pitch values even when voicing is not present. Therefore, in this paper on
UTI-based SSI, we use a simple continuous F0 tracker which does not apply a
strict voiced / unvoiced decision. Continuous vocoder parameters (ContF0,
Maximum Voiced Frequency and Mel-Generalized Cepstrum) are predicted using a
convolutional neural network, with UTI as input. The results demonstrate that
during the articulatory-to-acoustic mapping experiments, the continuous F0 is
predicted with lower error, and the continuous vocoder produces slightly more
natural synthesized speech than the baseline vocoder using standard
discontinuous F0.
