The method and a system is for locating and recording time-limited signal sequences in media channels that may contain undesirable signal components, e.g., recording music in radio transmissions. The signals are continuously buffered in a memory. The user identifies a desired source material. Out of this desired source material a section may be taken as a search key. The device may also select search keys automatically. If a second instance of the search key is detected, signal sequences that in time are connected to the search keys are compared. The signal sequences that by comparison are substantially identical are identified as belonging to the same, wanted, source material. The next step is an iteration of the above procedure results in a longer and higher quality segment of source material than the initial common segment.