 In the recording process, a sufficiently amplified audio signal was sent to a heavily weighted electromagnetic recording head with a blunt diamond stylus that indented, rather than cut or engraved, a sound-modulated groove into the surface of the metal.Normally, a completely blank disc was used and the recording head was slowly carried toward its center by a dedicated feed mechanism.Some low-end recording units economized by eliminating the feed mechanism, relying instead on the use of discs already cut with a narrow blank groove that guided the stylus, which simply impressed its vibrations into the upper region of the existing groove.