  This paper proposes singing voice synthesis (SVS) based on frame-level
sequence-to-sequence models considering vocal timing deviation. In SVS, it is
essential to synchronize the timing of singing with temporal structures
represented by scores, taking into account that there are differences between
actual vocal timing and note start timing. In many SVS systems including our
previous work, phoneme-level score features are converted into frame-level ones
on the basis of phoneme boundaries obtained by external aligners to take into
account vocal timing deviations. Therefore, the sound quality is affected by
the aligner accuracy in this system. To alleviate this problem, we introduce an
attention mechanism with frame-level features. In the proposed system, the
attention mechanism absorbs alignment errors in phoneme boundaries.
Additionally, we evaluate the system with pseudo-phoneme-boundaries defined by
heuristic rules based on musical scores when there is no aligner. The
experimental results show the effectiveness of the proposed system.
