Apparatus for encoding a multi-channel signal comprising at least two channels (101, 102), comprising: a downmixer for calculating a downmix signal from the multi-channel signal; a parameter calculator for calculating a side gain from a first channel of the at least two channels (101, 102) and a second channel of the at least two channels (101, 102) and for calculating a residual gain from the first channel and the second channel; and an output interface for generating an output signal, the output signal comprising information on the downmix signal, and on the side gain and the residual gain, wherein the parameter calculator is configured: to generate a sub-bandwise representation of the first channel and the second channel, to calculate (21, 22, 23, 24) a first amplitude-related characteristic of the first channel in a sub-band and to calculate a second amplitude-related characteristic of the second channel in the sub-band, to calculate an inner product of the first channel and the second channel in the sub-band; to calculate the side gain in the sub-band using a first relation involving the first amplitude-related characteristic, the second amplitude-related characteristic, and the inner product; and to calculate the residual gain in the sub-band using a second relation involving the first amplitude-related characteristic, the second amplitude-related characteristic, and the inner product, the second relation being different from the first relation, wherein the first amplitude-related characteristic and the second amplitude-related characteristic are determined from amplitudes, from powers, from energies or from any powers of amplitudes with an exponent greater than 1, and wherein the parameter calculator is configured to calculate the side gain and the residual gain so that the residual gain depends on the side gain, and wherein the output interface is configured to perform a joint quantization using groups of quantization points, each group of quantization points being defined by a fixed amplitude-related ratio between the first channel and the second channel. a downmixer for calculating a downmix signal from the multi-channel signal; a parameter calculator for calculating a side gain from a first channel of the at least two channels (101, 102) and a second channel of the at least two channels (101, 102) and for calculating a residual gain from the first channel and the second channel; and an output interface for generating an output signal, the output signal comprising information on the downmix signal, and on the side gain and the residual gain, wherein the parameter calculator is configured: to generate a sub-bandwise representation of the first channel and the second channel, to calculate (21, 22, 23, 24) a first amplitude-related characteristic of the first channel in a sub-band and to calculate a second amplitude-related characteristic of the second channel in the sub-band, to calculate an inner product of the first channel and the second channel in the sub-band; to calculate the side gain in the sub-band using a first relation involving the first amplitude-related characteristic, the second amplitude-related characteristic, and the inner product; and to calculate the residual gain in the sub-band using a second relation involving the first amplitude-related characteristic, the second amplitude-related characteristic, and the inner product, the second relation being different from the first relation, wherein the first amplitude-related characteristic and the second amplitude-related characteristic are determined from amplitudes, from powers, from energies or from any powers of amplitudes with an exponent greater than 1, and to generate a sub-bandwise representation of the first channel and the second channel, to calculate (21, 22, 23, 24) a first amplitude-related characteristic of the first channel in a sub-band and to calculate a second amplitude-related characteristic of the second channel in the sub-band, to calculate an inner product of the first channel and the second channel in the sub-band; to calculate the side gain in the sub-band using a first relation involving the first amplitude-related characteristic, the second amplitude-related characteristic, and the inner product; and to calculate the residual gain in the sub-band using a second relation involving the first amplitude-related characteristic, the second amplitude-related characteristic, and the inner product, the second relation being different from the first relation, wherein the first amplitude-related characteristic and the second amplitude-related characteristic are determined from amplitudes, from powers, from energies or from any powers of amplitudes with an exponent greater than 1, and wherein the parameter calculator is configured to calculate the side gain and the residual gain so that the residual gain depends on the side gain, and wherein the output interface is configured to perform a joint quantization using groups of quantization points, each group of quantization points being defined by a fixed amplitude-related ratio between the first channel and the second channel.