  In recent years, many works have investigated the feasibility of
conversational robots for performing specific tasks, such as healthcare and
interview. Along with this development comes a practical issue: how should we
synthesize robotic voices to meet the needs of different situations? In this
paper, we discuss this issue from three perspectives: 1) the difficulties of
synthesizing non-verbal and interaction-oriented speech signals, particularly
backchannels; 2) the scenario classification for robotic voice synthesis; 3)
the ethical issues regarding the design of robot voice for its emotion and
identity. We present the findings of relevant literature and our prior work,
trying to bring the attention of human-robot interaction researchers to design
better conversational robots in the future.
