ReaFir Noise Removal

Noise removal can be a pain to do. If you are in need of headroom or a clean signal, noise can have an impact as bad as ruining a take. Of course, there is professional software out there designed to eliminate noise, and many softwares come with a tool built in. You may think Reaper is lacking in this area. I can assure you that it is not! ReaFir is an excellent tool in the ReaPlugs suite which comes with Reaper by default. ReaPlugs is also available as VST for other DAWs to use, so it is luckily not limited to Reaper.

So how do we use ReaFir, and what is it? It is essentially a Fast Fourier Transform (FFT) dynamic processing unit. It analyses a signal and calculates the frequencies which are present in it as well as their phase.

To remove noise, you need to set it to subtract mode. What this mode does is measure the background frequencies in a region of silence and subtract them from the final signal, sort of like tareing a scale.

If there is a constant tone at 100Hz, it will subtract that from the recording by the same volume so it doesn't show up in the recording. Of course, noise tends to consist of more than one frequency, this measures them all and notes their intensity for subtraction.

To get started you need to build a noise profile by setting a loop on a portion of silence where the noise is present. It is therefore wise to factor in 10-15 seconds at the start or end of a recording for silence to do this.

Check the "Automatically build noise profile" box and play the "silence", making sure to avoid any speech in the section being profiled.

Once a noise profile has been built, uncheck the box and the noise should be significantly reduced. If you don't uncheck the box, it will continue measuring the frequencies to subtract, including those of your voice.

Below is an example of the subtraction profile made from a sample of noise, you can see the main frequencies which make up the noise, and their intensities.

This plugin can be used for more than just noise removal. Try playing about with building a subtraction profile out of various samples to see how they affect the sound. You can get really interesting static phase effects by sampling a snippet of an instrument and then applying the subtraction to the instrument track.

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