Listen to these examples to get an idea of how to rate:

Excellent - Completely natural speech - audio sample 1

Good - Mostly natural speech - audio sample 2

Fair - Equally natural and unnatural speech - audio sample 3

Poor - Mostly unnatural speech - audio sample 4

Bad - Completely unnatural speech - audio sample 5

Listen to the sample of computer generated speech and assess the quality of the audio based on how close it is to natural speech.

For better results, wear headphones and work in a quiet environment.