A research team undertook a study in 2016 to understand the appeal behind Mercury's voice. Led by Professor Christian Herbst, the team identified his notably faster vibrato and use of subharmonics as unique characteristics of Mercury's voice, particularly in comparison to opera singers. They confirmed a vocal range from F to G (just over 3 octaves) but were unable to confirm claims of a four-octave range. The research team studied vocal samples from 23 commercially available Queen recordings, his solo work, and a series of interviews of the late artist. They also used an endoscopic video camera to study a rock singer brought in to imitate Mercury's singing voice.