Audiovisual files hold a signal or an image, and so have a quality dimension that has no equivalent in text files. Digital Preservation projects provide guidance for optimizing the preservation of ‘significant properties’, but audiovisual content also have purely technical dimensions to preserve: signal fidelity and image quality. For digital libraries, automation of signal quality control is necessary, both at time of original input and for every migration or publication thereafter – because manual checking does not scale to large collections. The paper reviews quality control automation and presents a graphical approach to tracking quality over an item's entire life cycle.