In audio engineering, a fade is a gradual increase or decrease in the level of an audio signal. The term can also be used for film cinematography or theatre lighting in much the same way (see fade (filmmaking) and fade (lighting)). A recorded song may be gradually reduced to silence at its end (fade-out), or may gradually increase from silence at the beginning (fade-in). Fading-out can serve as a recording solution for pieces of music that contain no obvious ending. Both fades and crossfades are very valuable since they allow the engineer to quickly and easily make sure that the beginning and the end of any audio is smooth, without any prominent glitches. It is necessary that there is a clear section of silence prior to the audio. Fade-ins and -outs can also be used to change the characteristics of a sound, such as to soften the attack in vocals where very plosive (‘b’, ‘d’, and ‘p’) sounds occur. It can also be used to soften up the attack of the drum and/or percussion instruments. A crossfade can be manipulated through its rates and coefficients in order to create different styles of fading. Almost every fade is different; this means that the fade parameters must be adjusted according to the individual needs of the mix. Professional turntablists and DJs in hip hop music use faders on a DJ mixer, notably the horizontal crossfader, in a rapid fashion while simultaneously manipulating two or more record players (or other sound sources) to create "scratching" and develop beats. Club DJs in house music and techno use DJ mixers, two or more sound sources (two record players, two iPods, etc.) along with a skill called beatmatching (aligning the beats and tempos of two records) to make seamless dance mixes for dancers at raves, nightclubs and dance parties. Though relatively rare, songs can fade out then fade back in. Some examples of this are "Helter Skelter" and "Strawberry Fields Forever" by The Beatles, "Suspicious Minds" by Elvis Presley, "Shine On Brightly" by Procol Harum, "Sunday Bloody Sunday" by John Lennon and Yoko Ono, "That Joke Isn't Funny Anymore" by The Smiths, "Thank You" by Led Zeppelin, "In Every Dream Home A Heartache" by Roxy Music, "It's Only Money, Pt. 2" by Argent, "The Great Annihilator" by Swans, "(Reprise) Sandblasted Skin" by Pantera, "Illumination Theory" and "At Wit's End" by Dream Theater, "Future" by Paramore, "Doomsday"