Restoration VPI's  -  Sprocket DeHum

Sprocket DeHum is a VPI for the restoration of optical film soundtracks, which are typically disturbed by 'sprocket buzz' of 24 Hz and 96 Hz (hum fundamental with harmonics). This disturbance (caused by incidence of light at the frame area and the perforation for transport) gets automatically removed, using 'intelligent' notch filters that switch themselves off if the desired modulation is masking the buzz signal. Also these filters are capable of following frequency changes due to wow and flutter or shrinking of the film during storage.

A detailed spectral analysis ranging from 20 to 30 Hz (or 85 to 105 Hz) allows to clearly identify the noise peak representing the fundamental hum frequency. The realtime 'Learn' function analyzes the audio signal, defines the dominant harmonics of the disturbance and then creates a harmonically related filter set, which is ordered by descending attenuation requirements. This allows easy removal of the most prominent harmonics only, with the least required number of filters, set by the 'Complexity' slider.

All in all this results in a very clean restoration process that doesn't affect the original signal's desired modulation.