Noise Reduction

Menu Command: Effect | Filter | Noise Reduction

Noise reduction helps eliminate unwanted noise within a sound, such as a background hiss, a power hum, or random interference. It cannot be used to separate or remove complex sounds, such as vocals from music or coughing/laughing.

You are presented with a spectral analysis window, with a shape line, and several other controls. The X and Y coordinates are updated when you click-and-drag a shape point. The X coordinate is the frequency in Hertz and the Y coordinate is the magnitude in decibels. The time of the spectral analysis shown is given in the Time box. If you move the time scroll bar, located below the analysis window, the graph changes to show the spectral analysis of a different part of the sound.

A reduction envelope is used to remove noise. The envelope can be created in four different ways, depending on the Reduction envelope setting as explained below. The Use clipboard option often gives the best results.

Use shape
Lets you manually create an envelope shape or select a preset shape. See Shape Controls for information about creating shapes. By setting a horizontal line at about 80dB, you can remove a hiss from a sound. The shape is used only if the Use shape envelope option is selected. Otherwise it is ignored. Presets allow you to store or recall shapes.

Use current spectrum
Creates an envelope based on the shape of the spectral analysis graph shown in the window. This is useful for removing a buzz, hum, or hiss. Before using this effect, find a time in the sound where only the noise can be heard. Use that time for the analysis window by adjusting the time scroll bar. Select this option, then choose OK. If the noise is consistent through the sound, this is the easiest setting to use.

Use average
Applies an averaging envelope throughout noise reduction processing. The envelope is continuously updated. Use this setting if the noise changes throughout the sound.

Use clipboard
Analyzes the audio in the clipboard and creates an envelope based on it. To use this setting, you must first copy part of the sound where the noise exists by itself. Like the Use current spectrum setting, this can remove a buzz, hum, static, and other common noises. The clipboard noise can be based on audio copied from another file or audio outside the current selection. In general, this is the best setting to use.

Settings
The FFT size determines the detail of the spectral analysis and the noise reduction envelope. Usually values of 11 to 12 give the best results. The Overlap value specifies the amount of audio to overlap from one calculation to the next. A value of 4x is fastest. The Scale value lets you alter the reduction envelope scale. A value of 100 uses the envelope as it is. A value of 200 doubles the envelope, which doubles the amount audio removed from the sound. A value of 50 halves the envelope, which halves the amount removed. Normally it should be set to 100. Use a lower value if you hear any tinkling distortion. The Output noise only option makes the effect perform the exact opposite of noise reduction so that only the noise remains in the output. This is useful when previewing the effect to hear what is actually being removed from the audio. Do not check this box when removing noise.