7. Evaluation of the synthesis

7.1 Black box or glass box

Synthesis evaluation is necessary to compare systems with each other and to measure progress. Evaluation of synthesis speech can be global (the signal generated) or focused on one aspect of the system.

Overall evaluation is generally that of the customer, who listens to and evaluates the synthesizer on the speech produced. Component evaluation is of more interest to the researcher or developer, who is looking to improve an aspect of the system.

Text-to-speech synthesis is a chain of processes, from text to acoustic signal. It is therefore the weakest link in the chain that will limit its quality, hence the importance of evaluating each module (analytical or internal evaluation, or "glass box"), in addition...