1. A method for processing an audio signal at an audio decoder, the method comprising: receiving a downmix signal, a residual signal, and object information; extracting a background-object signal and a foreground-object signal from the downmix signal using the residual signal and the object information; receiving mix information including gain information for the background-object signal; generating downmix processing information based on the object information and the mix information; and generating an output audio signal including a modified background-object signal and a modified foreground-object signal, wherein the modified background-object signal is obtained by modifying a gain of the background-object signal using the mix information, and wherein the modified foreground-object signal is obtained by modifying a gain of the foreground-object signal using the downmix processing information.