In this final section we will consider desired developments in the field of speech output testing, and discuss possibilities for further research on a more general level than we did in the preceding sections. The section consists of three parts. In the first part (Section 12.6.2) we will be concerned with possibilities of producing more efficient output testing techniques. The general, longer-term strategy proposed here is to replace expensive, time-intensive tests (involving human listeners in field situations) by cheaper, automated tests carried out in a laboratory setting . In order to make this feasible we will have to establish predictability relationships between the various types of tests discussed in Section 12.2:
Next, we will discuss (Section 12.6.3) developments that we feel are needed in the assessment of linguistic interfaces of speech output systems. Finally, in Section 12.6.4, we will propose research for the mid term aimed at improving speech output evaluation at the acoustic level in each of the four areas identified: segmental quality (Section 12.6.4), prosodic quality (Section 12.6.4), voice characteristics (Section 12.6.4), and overall quality (Section 12.6.4).