About Detection Errors

The system can make three kinds of mistakes when operated in the automatic detection (DeClick Plus) mode: it can overlook noise pulses, raise false alarms, or mark the corrupted fragments inaccurately. Understanding the reasons for different mistakes will help you deal with them appropriately.

Overlooked noise pulses and false alarms

DART XP Pro may occasionally overlook noise pulses or raise false alarms. In the latter case, it schedules for reconstruction some genuine parts of the signal, classified mistakenly as outliers. Errors of both kinds are practically unavoidable as they are an inherent part of any decision process. Moreover, when you try to minimize the number of errors of the first kind, the second kind is most likely to occur and vice versa.

The intensity of false alarms is related to the adopted detection threshold. Increasing the detection threshold can decrease the number of false alarms. The sensitivity of the detector decreases at the same time, which means that the system is now prone to overlook a larger number of outliers. If the threshold is too low, the detector starts to behave 'hysterically', objecting to the slightest departures of signal from its regular pattern. The default value of the detection threshold seems to be a reasonable compromise between the two tendencies mentioned above, and yields satisfactory results for a large variety of audio signals. Nevertheless, it does not guarantee 100 % accuracy.

Unless false alarms occur too frequently, most of them do not create any problems, simply because the system tends to replace suspicious looking signal features with almost identical ones (this is like replacing one good floor tile with another good one). Some difficulties may arise in two cases

When signal characteristics change abruptly (e.g. when an entirely different sound starts to build up), DART XP Pro may reject and replace a small portion of the material before it readjusts internal parameters and tunes itself to a new situation. In most cases, the effects of such censorship are not noticeable. All the system does is slightly prolong the sound observed prior to the sudden change. Sometimes, however, such interventions result in audible distortions.

Pitch excitation, typical of a voiced speech, is another source of potential problems. Since the pitch frequency can change dramatically (up to 40% over one period of variation!), the system may occasionally confuse pitch impulses with outliers, causing local degradation of the restored signal.

Inaccurate marking

From time to time the system may inaccurately mark the material to be reconstructed. For example, some scratch pulses have very soft edges and are therefore extremely difficult to position. It may also happen that the disturbance lasts too long for the detector to handle it properly - not more than 100 samples in a row can be called in question in the auto detection mode.

Editing a detection file