An audio-processing device having an audio input, for receiving audio signals, each audio signal having a mixture of components, each corresponding to a sound source, and a control input, for receiving, for each sound source, a desired gain factor associated with the source, by which it is desired to amplify the corresponding component, and an auxiliary signal generator, for generating at least one auxiliary signal from the audio signals, and with a different mixture of components as compared with a reference audio signal; and a scaling coefficient calculator, for calculating scaling coefficients based upon the desired gain factors and upon parameters of the different mixture, each scaling coefficient associated with one of the auxiliary signal and optionally the reference audio signal, and an audio synthesis unit, for synthesizing an output audio signal by applying scaling coefficients to the auxiliary signal and optionally the reference audio signal and combining the results.