The germanium material is placed in proximity with opposing magnetic fields. A variety of coheres such as the coal dust detector. A cohere is a signal detection device that has loosely packed particle that are acted on by electromagnetic energy. No detector at all. Although few, it is possible to record messages without anything connected to the input of the recording device.
Any rectification can turn ambient electromagnetic energy into a usable signal.
A microphone detector is the most commonly used and may be the most effective considering our current level of understanding. The voices involved in EVP messages often exhibit a shift in frequency outside of the normal human voice, frequency range. The human voice generally ranges between 300 Hz and 1000 Hz. Although broad, there is a pattern in the type of entity communicating with experimenters. An entity who has never lived in the physical.