Low-Pass Filter - Audacity Manual

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Low-Pass Filter passes frequencies below its cutoff frequency and attenuates frequencies above its cutoff frequency. This effect can therefore be used to reduce high pitched noise.
Advice Note carefully that when you apply an effect to a time-stretched clip the changed speed of the clip will be automatically rendered.
  • If you apply an effect to a selection within a time-stretched clip then Audacity will split the original clip so that the selection can be rendered as part of applying the effect.
Alert If you apply this effect with an envelope present then there is a bug whereby the envelope is removed and the audio reverts to its full amplitude state prior to the effect being applied.
Accessed by: Effect > EQ and Filters > Low-Pass Filter Low-Pass Filter 3-5-0.png

Frequency (Hz)

Sound above this cutoff frequency in Hz is not eliminated but increasingly attenuated as the frequency rises further above the cutoff.

The cutoff frequency (sometimes also called corner frequency) defines the point at which the audio is reduced by 3 dB. Thus there will also be a small and decreasing amount of attenuation just below the cutoff frequency as in the following image.

250Hz low-pass.png

Roll-off (dB per octave)

Roll-off sets the steepness of the attenuation above the corner frequency. Higher roll-off values give a steeper slope to the attenuation. For example, with a roll-off of 6 dB per octave, the sound decreases by 6 dB in amplitude for each octave above the cutoff frequency (an octave above is double the frequency).

Tip To achieve more attenuation, run the effect again or use a greater roll-off.

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