We evaluate CBA, LSA, DCA, and GMMv2b using mean opinion score (MOS) naturalness judgments produced by a crowd-sourced pool of raters. Scores range from 1 to 5, with 5 representing “completely natural speech”. 
 Question: How they compare varioius mechanisms in terms of naturalness?
using mean opinion score (MOS) naturalness judgments produced by a crowd-sourced pool of raters