Cube-Tec’s RepairFilter for Digidesign Pro Tools combines an intuitive analytical tool with eight tracking notch filters and a highpass/lowpass filter set. The software is designed to simplify the process of identifying and removing steady-state disturbances in old optical film sound recordings, mains hum and harmonics, video monitor line whistles, lighting buzz, musical instrument amplification buzz and idle tones from A/D.
The audio signal is displayed in a real-time spectrogram, which shows the last three seconds of playback history, where frequencies are mapped on the y-axis and time on the x-axis. Amplitudes of frequencies are displayed using a color spectrum. The color spectrum can be compressed into a limited dynamic range to provide better contrast with low-level signals. It’s possible to zoom in on any frequency range to provide high-resolution displays of static tones and other frequency-based disturbances. It’s also possible to view the left channel, right channel or a sum of both channels.
Normally, the histogram scrolls with audio playback, but a Freeze button stops the display so that it’s easier to analyze a section and position the mouse over a specific section. Hovering the mouse over an area will pop up frequency/amplitude statistics of that precise spot for setting notch filter parameters such as frequency and bandwidth.
The eight tracking notch filters have three operating modes: Auto, Edit and Cursor. In Auto mode, each notch filter will search for a steady-state tone and automatically set its center frequencies and bandwidth. Attenuation is normally set automatically by the plug-in through the use of psychoacoustic “masking threshold” algorithms. Using the Gain and Processing Threshold values can modify these.
In Cursor mode, the operator can click on the spectrogram frequency axis to set the filters’ center frequency. In Edit mode, exact center frequencies can be entered manually, using numeric entry.