The Doom soundtrack was composed by Mick Gordon, with additional contributions by Richard Devine. Gordon aimed to treat the game's original soundtrack with "utmost respect" while modernizing it; however, the team at id stipulated in the initial brief that they wanted "no guitars" on the soundtrack, fearing that it would make the game "feel like Bill & Ted" and that heavy metal music itself has become "a bit of a joke". Gordon's initial concept was based around the idea of Argent energy corrupting human-made devices; to mirror this in music, he fed basic waveforms – sine waves and white noise – through a complex array of effects units such as distortion and compression. While this resulted in a unique electronic sound, the game still wasn't "sounding like Doom"; Gordon then gradually started adding more and more guitar elements, which eventually resulted in the desired tone and feel for the game; Gordon used seven- and eight-string guitars to give the music a lower tone, and used a nine-string guitar for the game's main theme, a variation on Bobby Prince's "E1M1" / "At DOOM's Gate" theme; Gordon would eventually admit that using a nine-string was "kinda stupid" in its excess, and that while he eventually sold the guitar to Fredrik Thordendal from Meshuggah, "even he can't find a use for it". The soundtrack contains numerous easter eggs: some songs reference themes or sounds from older Doom games, others contain backmasking ("Jesus loves you"), images of pentagrams and the number 666 embedded into the sound via steganography. Gordon intended these as a joke, and never thought anyone would find them, but they were discovered shortly after release and widely covered in the media.