Audio encoder (2") for encoding a multichannel signal, comprising: a downmixer for downmixing the multichannel signal to obtain a downmix signal; a linear prediction domain core encoder for encoding the downmix signal to obtain an encoded downmix signal, wherein the downmix signal has a low band and a high band, wherein the linear prediction domain core encoder is configured to apply a bandwidth extension processing for parametrically encoding the high band; a filterbank for generating a spectral representation of the multichannel signal; and a joint multichannel encoder configured to process the spectral representation comprising the low band and the high band of the multichannel signal to generate multichannel information, wherein the linear prediction domain core encoder comprises an ACELP processor, wherein the ACELP processor is configured to operate on a downsampled downmix signal obtained from the downmix signal by a downsampler, and wherein a time domain bandwidth extension processor is configured to parametrically encode the high band of the downmix signal removed from the downmix signal by the downsampling using the downsampler, and wherein the linear prediction domain core encoder comprises a TCX processor, wherein the TCX processor is configured to operate on the downmix signal not downsampled or downsampled by a degree smaller than the downsampling for the ACELP processor performed by the downsampler, the TCX processor comprising a time-frequency converter, a parameter generator for generating a parametric representation of a first set of bands, and a quantizer encoder for generating a set of quantized encoded spectral lines for a second set of bands. a downmixer for downmixing the multichannel signal to obtain a downmix signal; a linear prediction domain core encoder for encoding the downmix signal to obtain an encoded downmix signal, wherein the downmix signal has a low band and a high band, wherein the linear prediction domain core encoder is configured to apply a bandwidth extension processing for parametrically encoding the high band; a filterbank for generating a spectral representation of the multichannel signal; and a joint multichannel encoder configured to process the spectral representation comprising the low band and the high band of the multichannel signal to generate multichannel information, wherein the linear prediction domain core encoder comprises an ACELP processor, wherein the ACELP processor is configured to operate on a downsampled downmix signal obtained from the downmix signal by a downsampler, and wherein a time domain bandwidth extension processor is configured to parametrically encode the high band of the downmix signal removed from the downmix signal by the downsampling using the downsampler, and wherein the linear prediction domain core encoder comprises a TCX processor, wherein the TCX processor is configured to operate on the downmix signal not downsampled or downsampled by a degree smaller than the downsampling for the ACELP processor performed by the downsampler, the TCX processor comprising a time-frequency converter, a parameter generator for generating a parametric representation of a first set of bands, and a quantizer encoder for generating a set of quantized encoded spectral lines for a second set of bands.