Skeptics such as David Federlein, Chris French, Terence Hines and Michael Shermer say that EVP are usually recorded by raising the "noise floor" – the electrical noise created by all electrical devices – in order to create white noise. When this noise is filtered, it can be made to produce noises which sound like speech. Federlein says that this is no different from using a wah pedal on a guitar, which is a focused sweep filter which moves around the spectrum and creates open vowel sounds.