<p><br /> Teen superstar Justin Bieber is said to have taken on a vocal coach to stop him from losing his trademark voice during puberty.<br /> </p><p><br /> The singer, who has complained that he now struggles to hit high notes in his breakout song 'Baby,' has drafted in a top trainer to help him.<br /> </p><p><br /> A spokesperson for the star said: "Justin is physically developing at a slower rate than most guys so his voice is only breaking now. He's working with the best in the business, a specialist called Jan Smith, to make sure he gets much vocal rest as humanly possible for a working pop star."<br /> </p><p><br /> Bieber's mentor Usher used the same voice coach to help him when his voice broke.<br /> </p><p><br /> Concerns for his vocals were not enough to stop the teen from chatting to X Factor judge Cheryl Cole as he performed on the show last night. The 16 year old was seen making a 'call me' hand gesture towards her as he left the stage.<br /> </p><p><br /> Later he tweeted, 'Cheryl u looked lovely as usual #sofine.'<br /> </p>
