20 Hz is considered the normal low frequency limit of human hearing. When pure sine waves are reproduced under ideal conditions and at very high volume, a human listener will be able to identify tones as low as 12 Hz.[2] Audio tracks known as bass tests use sub-bass frequencies which are used to test or to demonstrate the capabilities of audio equipment. Very few subwoofers can reproduce sound below 30 Hz. Sub-bass energy is popular in dance music and dub reggae, where the low frequencies involve energy from the kick drum, the bass guitar and electronic synthesizers. Other genres such as dubstep often feature the whole bass-line reproduced in sub-bass frequencies, perhaps with sub-bass guitar rather than bass guitar. Much experimental music uses sub-bass, in particular drone music, where the majority of the sound can often be in the sub-bass range. Heavy metal bands such as Cephalic Carnage, Avenged Sevenfold, Guns N' Roses and The Devil Wears Prada have used sub-bass drops in their songs