Autodesk 64006-051108-9001 User Guide - Page 90

82 Chapter 6: Pre-processing Unlike the Noise Removal, Notch, High Pass and Low Pass filters, which remove specific frequencies throughout the whole length of the source, the Noise Gate totally silences the entire signal when it goes below a certain volume (amplitude) for a specific amount of time, such as between words or sentences in speech. Generally, the Noise Reduction/Notch filters should be used first and the Noise Gate added if there is still noticeable noise in areas that should be silent. Note: You should not use the Noise Gate with material which has a background sound track, or other continuous sound. This filter is only useful with material that has sections that should be totally silent. Custom Noise Gate The Custom Noise Gate setting has two controls. The Threshold controls the level under which the Noise Gate totally silences the audio track. The higher the setting, the louder the sections the Noise Gate silences. If you set the Threshold too high, the Noise Gate can remove meaningful parts of the audio, which can sound very odd. For example, quieter parts of the narration may get silenced. If you set it too low, the Noise Gate may never activate, and the audio is not altered. The Minimum Duration controls how long a quiet section must last before the Noise Gate silences it. Setting this to a very short duration can cause narration to get choppy as the Noise Gate silences spaces between words or syllables. Notch The Notch filter removes a group of frequencies centered on a specified frequency. Whereas the High and Low Pass filters eliminate frequencies at the ends of the audio spectrum, this filter removes a notch of frequencies in the middle. This is often useful for removing a specific offending frequency, such as AC power line noise. Line noise is generally 60 Hz in the U.S., 50 Hz in Europe. The preset options relate to common power line frequencies. If your source suffers from line noise, try one of these settings first. If you are unable to effectively remove the line noise with the preset, or if your source has different frequency noise, the Custom option may be helpful.