Gapless playback is the uninterrupted playback of consecutive audio tracks, such that relative time distances in the original audio source are preserved over track boundaries on playback. For this to be useful, other artifacts (than timing related) at track boundaries should not be severed either. Gapless playback is common with compact discs, gramophone records, or tapes, but is not always available with other formats that employ compressed digital audio. The absence of gapless playback is a source of annoyance to listeners of music where tracks are meant to segue into each other, such as some classical music (opera in particular), progressive rock, concept albums, electronic music, and live recordings with audience noise between tracks.