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Filter curve: Contents and Utility

You might know about the Fast Fourier Transform filter. The Filter curve is this type of filter, and is an equalization tool. What does we mean by equalization? Equalization is the process of manipulating sounds through frequency. You can increase or decrease the frequency. The filter curve dialog box appears with the following contents.

Draw EQ Filter Curves

The white circles joining together compose a blue curve. The green curve follows the blue curve. Control points are white circles. You can click at any position in the graph to draw the blue curve or drag the blue curve. When you click to create the blue curve, a white circle is formed. This white circle is the control point. As you move forward to draw the curve, more white circles are formed.

Consider that there are some limitations to the equalization algorithm. Audacity uses the green curve that follows the path of the blue curve to apply the effect. Because, the green curve is smoother than the blue curve.

There is a checkbox for a linear frequency scale. This changes the frequency scale to either linear or logarithmic. Check the checkbox if you want a linear frequency scale. Use this scale when you want the high frequencies to be precise. If you want a logarithmic scale then uncheck the checkbox, as this focuses on lower frequencies.

Filter Curve

Graph Scale and Sliders

The scale that you see on the filter curve has separate units. The vertical scale on the graph denotes the gain. It applies this gain to the given frequency, and is in decibels. The horizontal scale contains frequency measurement, which is in Hertz.

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On the left side of the dialog box, you can see two vertical scale sliders. The vertical scale is set to +30 dB to -30 dB. You can change this range of the vertical scale from the vertical sliders. Individually, change the upper or lower dB range or both as you wish.

Equalization settings

Flatten button is a quicker way for you to set the level response curve. This draws the curve from left to right. The vertical scale position of this curve is 0 dB. This suggests the volume level of all frequencies remain the same. The invert button does what the name suggests: it converts the curve upside down. The show grid lines checkbox shows the grid lines on the window.


The Manage, Preview, OK and Cancel buttons all have different functionalities. Manage allows you to save your custom curves and restore them. The preview button plays the preview of the effect on the audio. The OK button applies the effect to the audio. The Cancel button cancels the application of any effect on the audio. The audio remains unchanged and the dialog box closes.


To perform equalization on the track, one requirement is significant. And, all of the audio tracks must have the same sample rate. You can change the track sample rate without changing the speed and pitch of the audio.


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