An audio processing system, comprising: a memory configured to store a neural network trained to process an audio mixture to output estimation of at least a subset of a set of audio sources present in the audio mixture, wherein the audio sources are subject to hierarchical constraints enforcing a parent-children hierarchy on the set of audio sources, such that a parent audio source in the parent-children hierarchy is a mixture of its multiple children audio sources, wherein the parent-children hierarchy is predefined, wherein the subset includes at least one parent audio source and at least one of its children audio sources, and wherein the subset corresponds to a path (121, 123) on the parent-children hierarchy of the set of audio sources starting at a root node till a leaf node; an input interface configured to receive an input audio mixture; a processor configured to process the input audio mixture using the neural network to extract estimates of the subset of audio sources and their mutual relationships according to the parent-children hierarchy; and an output interface configured to render the extracted audio sources and their mutual relationships; wherein the processor is coupled with stored instructions implementing modules of the audio processing system, including: a spectrogram extractor module configured to produce a spectrogram for a sequence of frames of the input audio mixture; a mask determination module configured to form outputs of the neural network into a set of masks corresponding to the extracted audio sources at different levels of parent-children hierarchy, such that an application of a mask to the spectrogram extracts the corresponding audio source, wherein the hierarchical constraints enforce that masks at higher levels in the parent-children hierarchy apportion at least the same amount of energy as masks at lower levels in the parent-children hierarchy; a source selector module configured to select masks in the set of masks according to a target output; and a spectrogram inverter module configured to apply the selected masks to the spectrogram to extract the audio sources from the input audio mixture; and wherein the hierarchical constraints enforce that any time-frequency regions in the spectrogram that the neural network assigns to the multiple children audio sources also is assigned to the parent source. a memory configured to store a neural network trained to process an audio mixture to output estimation of at least a subset of a set of audio sources present in the audio mixture, wherein the audio sources are subject to hierarchical constraints enforcing a parent-children hierarchy on the set of audio sources, such that a parent audio source in the parent-children hierarchy is a mixture of its multiple children audio sources, wherein the parent-children hierarchy is predefined, wherein the subset includes at least one parent audio source and at least one of its children audio sources, and wherein the subset corresponds to a path (121, 123) on the parent-children hierarchy of the set of audio sources starting at a root node till a leaf node; an input interface configured to receive an input audio mixture; a processor configured to process the input audio mixture using the neural network to extract estimates of the subset of audio sources and their mutual relationships according to the parent-children hierarchy; and an output interface configured to render the extracted audio sources and their mutual relationships; wherein the processor is coupled with stored instructions implementing modules of the audio processing system, including: a spectrogram extractor module configured to produce a spectrogram for a sequence of frames of the input audio mixture; a mask determination module configured to form outputs of the neural network into a set of masks corresponding to the extracted audio sources at different levels of parent-children hierarchy, such that an application of a mask to the spectrogram extracts the corresponding audio source, wherein the hierarchical constraints enforce that masks at higher levels in the parent-children hierarchy apportion at least the same amount of energy as masks at lower levels in the parent-children hierarchy; a source selector module configured to select masks in the set of masks according to a target output; and a spectrogram inverter module configured to apply the selected masks to the spectrogram to extract the audio sources from the input audio mixture; and a spectrogram extractor module configured to produce a spectrogram for a sequence of frames of the input audio mixture; a mask determination module configured to form outputs of the neural network into a set of masks corresponding to the extracted audio sources at different levels of parent-children hierarchy, such that an application of a mask to the spectrogram extracts the corresponding audio source, wherein the hierarchical constraints enforce that masks at higher levels in the parent-children hierarchy apportion at least the same amount of energy as masks at lower levels in the parent-children hierarchy; a source selector module configured to select masks in the set of masks according to a target output; and a spectrogram inverter module configured to apply the selected masks to the spectrogram to extract the audio sources from the input audio mixture; and wherein the hierarchical constraints enforce that any time-frequency regions in the spectrogram that the neural network assigns to the multiple children audio sources also is assigned to the parent source.