A method in a decoder of a multi-channel audio processing system, comprising the steps of: receiving M upmix signals comprising spectral coefficients corresponding to frequencies above a first cross-over frequency k y, wherein the M upmix signals is the result of an upmix of N frequency extended downmix signals into M upmix signals, each of the M upmix signals corresponding to a respective one of M encoded channels, wherein 1<N<M; receiving a waveform-coded signal comprising spectral coefficients corresponding to a frequency interval starting from the first cross-over frequency k y; receiving M waveform-coded signals comprising spectral coefficients corresponding to frequencies up to the first cross-over frequency, each of the M waveform-coded signals corresponding to a respective one of the M encoded channels; and interleaving the waveform-coded signal with one of the M upmix signals such that an interleaved version of said one of the M upmix signals is obtained, characterized by further comprising: receiving a control signal indicating time/frequency tiles for which the waveform-coded signal is to be interleaved with one of the M upmix signals, wherein the control signal comprises a first vector indicating frequency intervals of the time/frequency tiles and a second vector indicating time intervals of the time/frequency tiles, and wherein the interleaving is performed under control of the control signal such that interleaving is performed in the time/frequency tiles indicated by the control signal; and combining the M waveform-coded signals with the M upmix signals before the interleaving, after the interleaving, or in a combined step with the interleaving. receiving M upmix signals comprising spectral coefficients corresponding to frequencies above a first cross-over frequency k y, wherein the M upmix signals is the result of an upmix of N frequency extended downmix signals into M upmix signals, each of the M upmix signals corresponding to a respective one of M encoded channels, wherein 1<N<M; receiving a waveform-coded signal comprising spectral coefficients corresponding to a frequency interval starting from the first cross-over frequency k y; receiving M waveform-coded signals comprising spectral coefficients corresponding to frequencies up to the first cross-over frequency, each of the M waveform-coded signals corresponding to a respective one of the M encoded channels; and interleaving the waveform-coded signal with one of the M upmix signals such that an interleaved version of said one of the M upmix signals is obtained, characterized by further comprising: receiving a control signal indicating time/frequency tiles for which the waveform-coded signal is to be interleaved with one of the M upmix signals, wherein the control signal comprises a first vector indicating frequency intervals of the time/frequency tiles and a second vector indicating time intervals of the time/frequency tiles, and wherein the interleaving is performed under control of the control signal such that interleaving is performed in the time/frequency tiles indicated by the control signal; and combining the M waveform-coded signals with the M upmix signals before the interleaving, after the interleaving, or in a combined step with the interleaving. receiving a control signal indicating time/frequency tiles for which the waveform-coded signal is to be interleaved with one of the M upmix signals, wherein the control signal comprises a first vector indicating frequency intervals of the time/frequency tiles and a second vector indicating time intervals of the time/frequency tiles, and wherein the interleaving is performed under control of the control signal such that interleaving is performed in the time/frequency tiles indicated by the control signal; and combining the M waveform-coded signals with the M upmix signals before the interleaving, after the interleaving, or in a combined step with the interleaving.