They can have solid, semi-hollow or hollow bodies and rely solely on amplification to produce sound. A single-coil or humbucker type electromagnetic pickup converts the vibration of the steel string into an electrical signal, which is then fed to the amplifier via a cable or radio transmitter. Steel strings and their electronic amplification make electric guitars far superior to more traditional acoustic guitars in terms of various techniques that can be performed, such as percussion, pull-off, and hammering (also known as connection), kneading harmonics, and increasing volume.