1. A method of processing acoustic data representing audio from a plurality of different acoustic sources mixed together to extract the audio from an individual one of the acoustic sources so that it can be listened to separately, the method comprising performing blind source separation by: inputting acoustic data from a plurality of acoustic sensors, said acoustic data comprising acoustic signals combined from said plurality of acoustic sources; converting said input acoustic data to combined source time-frequency domain data representing said acoustic signals combined from said plurality of acoustic sources, wherein said time-frequency domain data is represented by an observation matrix X ƒ for each of a plurality of frequencies ƒ; performing an independent component analysis (ICA) on said observation matrix X ƒ to determine a demixing matrix W ƒ for each said frequency such that an estimate Y ƒ of the acoustic signals from said plurality of acoustic sources at said frequencies ƒ is determined by X ƒ W ƒ ; wherein said ICA is performed based on an estimation of an individual source spectrogram of each individual said acoustic source; and wherein said estimation of said individual source spectrogram of each individual said acoustic source is determined from a model of said individual acoustic source, the model representing individual source time-frequency variations in a signal output of said individual acoustic source; using said demixing matrix W ƒ to process said acoustic data comprising acoustic signals combined from said plurality of acoustic sources and demix individual acoustic data for an individual one of said plurality of acoustic sources; and providing the acoustic data for the individual one of said plurality of acoustic sources to an output device for transmission to a user.