A method of decoding an audio signal including at least one audio object, comprising: receiving a downmix signal, DMX, object information, OI, and rendering information obtaining downmix gain flag information, DMG_flag, indicating whether a downmix gain,D, is included in the object information, OI; extracting modified object level information, MOLD, from the OI, if the downmix gain flag information, DMG_flag, indicates that the downmix gain is not included in the object information, wherein the MOLD indicates a level of a modified audio object, Ŝ i, the modified audio object (Ŝ i) being generated by applying a downmix gain, D i, to an audio object, S i, by the following formula: S ^ i = D i S i, wherein i is the number of each object; and wherein the MOLD is represented bv the following formula: MOLD i pb = ∑ n ∑ m ∈ pb s ^ i n. m s ^ i n. m * max k ∑ n ∑ m ∈ pb s ^ k n, m s ^ k n. m * wherein ′ s ^ i n. m ′ is a modified audio object on a sub-band defined by a time slot 'n' and a sub-band 'm'; extracting object level information, OLD and the downmix gain, D, from the OI, if the downmix gain flag information, DMG_flag, indicates that the downmix gain, D is included in the OI, wherein OLD indicates a level of an audio object, S i, wherein the OLD is represented by the following formula: OLD i pb = ∑ n ∑ m ∈ pb s i n. m s i n. m * max k ∑ n ∑ m ∈ pb s k n. m s k n. m * wherein ′ S i n, m ′ is an audio object on a sub-band defined by a time slot 'n' and a sub-band 'm'; and generating downmix processing information, DPI, and multi-channel information, MI, using the OI and the rendering information; generating a processed downmix signal, PDMX, by applying the DPI to the downmix signal, DMX; and decoding a multi-channel audio signal by applying the multi-channel information, MI, to the processed downmix signal, PDMX, wherein in case that the audio object generates a stereo downmix signal and the downmix gain D i include a pair of values (D 1,i, D 2,i), the modified audio object (Ŝ i) included in the stereo downmix signal are derived using modified downmix gains ( D̂ 1, i, D̂ 2, i) as following formulas, s ^ i = D 1, i 2 + D 2, i 2 s i s ^ 1, i = D ^ 1, i s ^ i s ^ 2, i = D ^ 2, i s ^ i wherein Ŝ 1, i and Ŝ 2, i are the modified audio objects included in left channel and right channel of the stereo downmix signal, respectively, wherein the modified downmix gains ( D̂ 1, i, D̂ 2, i) are normalized and derived as following formulas, D ^ 1, i = D 1, i / D 1, i 2 + D 2, i 2 D ^ 2, i = D 2, i / D 1, i 2 + D 2, i 2 D ^ 1, i 2 + D ^ 2, i 2 = 1. receiving a downmix signal, DMX, object information, OI, and rendering information obtaining downmix gain flag information, DMG_flag, indicating whether a downmix gain,D, is included in the object information, OI; extracting modified object level information, MOLD, from the OI, if the downmix gain flag information, DMG_flag, indicates that the downmix gain is not included in the object information, wherein the MOLD indicates a level of a modified audio object, Ŝ i, the modified audio object (Ŝ i) being generated by applying a downmix gain, D i, to an audio object, S i, by the following formula: S ^ i = D i S i, wherein i is the number of each object; and wherein the MOLD is represented bv the following formula: MOLD i pb = ∑ n ∑ m ∈ pb s ^ i n. m s ^ i n. m * max k ∑ n ∑ m ∈ pb s ^ k n, m s ^ k n. m * wherein ′ s ^ i n. m ′ is a modified audio object on a sub-band defined by a time slot 'n' and a sub-band 'm'; extracting object level information, OLD and the downmix gain, D, from the OI, if the downmix gain flag information, DMG_flag, indicates that the downmix gain, D is included in the OI, wherein OLD indicates a level of an audio object, S i, wherein the OLD is represented by the following formula: OLD i pb = ∑ n ∑ m ∈ pb s i n. m s i n. m * max k ∑ n ∑ m ∈ pb s k n. m s k n. m * wherein ′ S i n, m ′ is an audio object on a sub-band defined by a time slot 'n' and a sub-band 'm'; and generating downmix processing information, DPI, and multi-channel information, MI, using the OI and the rendering information; generating a processed downmix signal, PDMX, by applying the DPI to the downmix signal, DMX; and decoding a multi-channel audio signal by applying the multi-channel information, MI, to the processed downmix signal, PDMX, wherein in case that the audio object generates a stereo downmix signal and the downmix gain D i include a pair of values (D 1,i, D 2,i), the modified audio object (Ŝ i) included in the stereo downmix signal are derived using modified downmix gains ( D̂ 1, i, D̂ 2, i) as following formulas, s ^ i = D 1, i 2 + D 2, i 2 s i s ^ 1, i = D ^ 1, i s ^ i s ^ 2, i = D ^ 2, i s ^ i wherein Ŝ 1, i and Ŝ 2, i are the modified audio objects included in left channel and right channel of the stereo downmix signal, respectively, wherein the modified downmix gains ( D̂ 1, i, D̂ 2, i) are normalized and derived as following formulas, D ^ 1, i = D 1, i / D 1, i 2 + D 2, i 2 D ^ 2, i = D 2, i / D 1, i 2 + D 2, i 2 D ^ 1, i 2 + D ^ 2, i 2 = 1.