Under the original format, the guest artist(s) can eliminate mystery singers after each round, and ended with the last remaining mystery singer depending on the outcome of a duet performance by themselves.
Rounds
Each episode presents the guest artist with seven people whose identities and singing voices are kept concealed until they are eliminated to perform on the "stage of truth" or remain in the end to perform the final duet.
Visual round
The guest artist is given some time to observe and examine each mystery singer based on their appearance. Afterward, a muted video of each mystery singer that reveals only 0.3 seconds of their singing voice is played as an additional hint.
Introduction round
Each mystery singer self-introduces to guest artist and panelists. Good singers are telling the truth, while bad singers are allowed to lie.
Lip sync round
Each mystery singer performs a lip sync to a song; good singers mime to a recording of their own, while bad singers mime to a recording by someone else.
1. Interrogation round
The guest artist may ask questions to the remaining mystery singers. Good singers are required to give truthful responses, while the bad singers must lie.
2. Talent round (eps. 53—79)
The guest artist must describe one of the mystery singer's other talents, except "singing" itself. This may not be related to the "stage of truth", but depends on their identity.