We performed two experiments to ascertain whether vocal self-training improves speech clarity, particularly when the feedback speech is degraded by a hearing impairment simulator. Speech sounds before and after the training were recorded under noisy and quiet conditions and their speech clarity was evaluated by subjective listening tests using Scheffe’s paired comparison. We also analyzed the auditory modulation features to derive an index to explain the subjective clarity scores. The auditory modulation index highly correlated with subjective scores and seems a good candidate for predicting speech clarity.