A method of identifying and attributing identified quantitative use of a digital source audio file containing at least one musical section (202, 316, T 1 -T 4) and wherein said digital source audio file is selected, from a plurality of source audio files stored in a track database (104, 106, 107, 200), by at least one identifiable client device of a multiplicity of independently operable client devices, and wherein the digital source audio file is (a) locally usable at an identifiable first client device upon user-selected local operation at the identifiable first client device and (b) is selectively accessible to each of the multiplicity of client devices that are connected, over a network, to a server arranged to regulate access to the digital source audio file and the track database (106, 107), wherein the track database further stores associated audio file descriptions (210, 212) defining musically viable cross-fades or cuts between different musical sections in each digital source audio file, each viable cross-fade or cut defined by a point in real time corresponding to a point in musical time where an audibly seamless cross-fade or cut maintains musical rhythm, and where the method comprises: making a request to the server to access the digital source audio file, the request made by identifiable first client device; providing access to the digital source audio file to the identifiable first client device, said access including making available a unique identifier related specifically to the digital source audio file; and at the identifiable first client device, establishing local use of the digital source audio file by identifying locally used entry and exit points (210, 212) associated with use, performance or manipulation of at least one musical section in the digital source audio file at the identifiable first client device and generating tracking data corresponding to entry and exit points associated with said local use thereof; sending, to the server over the network, a report of said local use of at least a portion of the accessed digital source audio file at the identifiable first client device, the report associating the tracking data with the unique identifier to identify points in real time for audibly seamless cross-fades or cuts instigated at the identifiable first client device; from the perspective of the server (46, 111), recording an attribution of quantitative use of musical sections of the digital source audio file by the identifiable first client device having regard to the unique identifier and said reported tracking data. making a request to the server to access the digital source audio file, the request made by identifiable first client device; providing access to the digital source audio file to the identifiable first client device, said access including making available a unique identifier related specifically to the digital source audio file; and at the identifiable first client device, establishing local use of the digital source audio file by identifying locally used entry and exit points (210, 212) associated with use, performance or manipulation of at least one musical section in the digital source audio file at the identifiable first client device and generating tracking data corresponding to entry and exit points associated with said local use thereof; sending, to the server over the network, a report of said local use of at least a portion of the accessed digital source audio file at the identifiable first client device, the report associating the tracking data with the unique identifier to identify points in real time for audibly seamless cross-fades or cuts instigated at the identifiable first client device; from the perspective of the server (46, 111), recording an attribution of quantitative use of musical sections of the digital source audio file by the identifiable first client device having regard to the unique identifier and said reported tracking data.