1. A method for recognizing an operational state of a noise-generating object to be investigated that generates noise during operation, where the noise is not purposely generated by the noise-generating object, but results from the operation thereof, comprising: performing a two-stage process for generating an individually adapted statistical classification model of acoustic features, comprising: (a) in a first stage, generating a statistical basic classification model of acoustic features based on a plurality of acoustic sound recordings made during operation of at least one reference object in different conditions or at different times, the statistical basic classification model defining one or more acoustic features corresponding to different operational states of the at least one reference object and a statistical parameter for at least one acoustic feature; and (a) in a second stage, subsequent to the generation of the statistical basic classification model, generating an individually adapted statistical classification model specific to the noise-generating object by: making sound recordings of an operation of the noise-generating object, the noise-generating object being separate from the at least one reference object; determining acoustic feature measurements from the sound recordings of the noise-generating object; automatically adapting the statistical basic classification model of acoustic features generated for the at least one reference object, based on the acoustic feature measurements determined from the sound recording signals of the operation of the noise-generating object to obtain the individually adapted statistical classification model specific to the noise-generating object, wherein adapting the statistical basic classification model includes adjusting the statistical parameter for the at least one acoustic feature; applying the individually adapted statistical classification model, including the adjusted statistical parameter for the at least one acoustic feature, to further acoustic feature measurements determined from further sound recordings of the operation of the noise-generating object; and classifying, by the processor, the operational state of the noise-generating object based on the application of the individually adapted statistical classification model to the further acoustic feature measurements.