Auto Tune digitally alters the pitch of a note. It was originally used as a corrective tool in the studio, to bring slightly sharp or flat notes into tune, but it is now used in live performances too. Cher's song "Believe" was the first mainstream example of Auto Tune as a creative device; the parameters of the effect are set high so that the pitch correction is dramatic rather than subtle. This creates a distinctive "wobbly" sound. Kanye West frequently performs with Auto Tune on his voice to achieve a similar effect.
Although compression is a subtle sound effect, concert goers would likely notice the effects if it weren't used. Compression is an audio effect that limits the dynamic range of the sound source, typically the vocal microphone. It boosts quiet sounds and reduces the volume of loud ones. Without compression, subtle vocals would get lost under the noise from the other instruments and loud vocals would become distorted.
U2 guitar player "The Edge" has a distinctive guitar sound. U2 recordings such as "Where the Streets Have No Name" feature prominent examples of his characteristically echoing guitar. At U2 concerts, he recreates this effect using a TC Electronic 2290 digital delay unit and signal splitter. The pedal samples each note from the guitar and plays it back immediately after the original note, to create an echo effect. The signal splitter takes the original and delayed signal and sends both to separate amplifiers. This creates the illusion that the guitarist is playing two guitars at once.
This is a popular sound effect, particularly at rock concerts. In most applications, distortion is an undesirable buzzing or crackling that is caused when the signal is too strong. However guitar and bass players use distortion pedals that create a thick, fuzzy distortion. The distortion gives an electric guitar its characteristic "heavy" sound. Before distortion effects were widely available, guitar players had to improvise to create the sound they desired. Guitarist Link Wray admitted to slashing his amplifier speakers to emulate the sound of harmonic distortion.