The teen sensation has admitted his voice is dropping as he goes through puberty, and he can`t hit the same high notes as he used to when he recorded his present album, `My World 2.0`. He said: ""It cracks. Like every teenage boy, I`m dealing with it and I have the best vocal coach in the world. "Some of the notes I hit on `Baby` I can`t hit anymore. We have to lower the key when I sing live." The singer was forced to cancel an appearance in Australia yesterday morning (26.04.10) amid a huge crush as thousands of female fans waited to watch him perform. Police called off the concert amidst "mass scenes of hysteria" after 10 girls fainted. Canadian singer Justin, 16 - who was discovered on video website Youtube - was devastated by the cancellation and apologised to his devoted fans. He tweeted: "I love my fans and I am just as disappointed as everyone else with the news from this morning. I want to sing for my fans. I want to make this clear... I don`t cancel... I woke up this morning to the police cancelling the show for safety reasons. "I`m very happy about the welcome and the love from around the world, but I want everyone to still remember my fans` safety comes first (sic)."