A 1080 line variant of Test Card W (sometimes referred to unofficially as Test Card X) was used on the now-defunct BBC HD channel. It could be viewed every two hours as part of the BBC HD preview slot. When viewed, it was enhanced with 5.1 surround sound tests. A BLITS tone is played alongside, which plays test tones at different frequencies from each of the different surround sound speakers, with markers (such as L, R, C, LFE, Ls, Rs) appearing inside some of the grey boxes of the testcard. BBC HD closed in March 2013; therefore Test Card X is no longer broadcast.