An apparatus for deriving a multi-channel audio signal comprising a front-loudspeaker signal and a back-loudspeaker signal from an audio signal, the apparatus comprising an apparatus for generating an ambient signal from the audio signal, wherein the apparatus for generating the ambient signal from the audio signal comprises means for a lossy compression of a representation of the audio signal so as to obtain a compressed representation of the audio signal; and means for calculating a difference between the compressed representation of the audio signal and the representation of the audio signal so as to obtain a discrimination representation, the discrimination representation describing the difference between the representation of the audio signal and the compressed representation of the audio signal and describing those portions of the audio signal not played back in the lossily compressed representation, and wherein the means for lossy compression is configured such that signal portions exhibiting regular distribution of the energy or carrying a large signal energy are preferred to be included in the compressed representation; wherein the discrimination representation forms the ambient signal; an apparatus for providing the audio signal or a signal derived therefrom as the front-loudspeaker signal; and a back-loudspeaker-signal-providing apparatus for providing the ambient signal provided by the apparatus for generating the ambient signal or a signal derived therefrom as the back-loudspeaker signal. An apparatus for generating an ambient signal from an audio signal comprises means for lossy compression of a representation of the audio signal so as to obtain a compressed representation of the audio signal describing a compressed audio signal. The apparatus for generating the ambient signal further comprises means for calculating a difference between the compressed representation of the audio signal and the representation of the audio signal so as to obtain a discrimination representation. The apparatus further comprises means for providing the ambient signal using the discrimination representation.