Possible Clues:

• Sing silently, in a way
• Learner at first not taking part in developing spicy mime
• Keep the noise down when following the track?
• Fake it on stage, say
• 'Sing' without singing
• Audio and video alignment of speech
• Type of recording made by brass that's lower in auditorium
• Go through the motions in a music video?
• Align mouth move­ments with recorded speech
• Pretend to sing, perhaps