Apr 6, 2015

Reaper Tip - Reafir Madness

Intelligent Noise Reduction

One of the most critical things I need when post processing audio is a noise reduction filter. The room is pretty quiet yet there is still audible room noise. The noise sits around –60dB which is pretty far down but noticeably audible for anyone listening on headphones. I also like to use a noise gate to remove low level breathing, lip smacking and other distracting sounds. The problem is if you use a noise gate with room noise and you don’t add a track of room noise, it’s very noticeable when the gate kicks in. A properly used noise reduction filter makes this problem go away. A badly used noise reduction filter adds those tinkling high frequency artifacts that to my ear, are worse than the original noise. In theory they’re quieter than the noise but they are much more noticeable.  Reaper has a built-in plug-in called Reafir that is a multi-purpose tool for audio processing. So far I’ve only used it for noise reduction. Here’s how.
  1. SNAGHTML28b0342fThe first step is to use the Mode dropdown and select the Subtract option. Then select a piece of audio that has only steady room noise. No clicks, no chair sounds just whatever ambient noise you want to remove. You can loop this section of audio.
  2. Then enable the checkbox for Automatically build noise profile (enable during noise).
  3. Select an FFT size. I tried all of them and I ended up just using the 4K FFT to build the profile. Now hit Play on the transport bar and it will build up a waveform in the bottom of the display. Hit Stop. If the red line doesn’t move to follow the noise then something isn’t working. Make sure the checkbox in the upper right corner is enabled.

  • Once Reafir has a profile uncheck the checkbox from step 2. You no longer want to build a waveform. Here is where you have to use your ears. Select a minute or so of your audio and loop it.  You can apply the noise reduction differently from how you collected it. You can change the FFT size and listen. I found that I could hear artifacts with most of these settings. They higher the FFT size the worse the artifacts seemed to get. This led me to use the Edit mode drop down and select the Points (smooth) option. I don’t know precisely what this does but I suspect it changes from a 4,000 point filter to a 7 band filter. You would think this would be horrible but it sounded quite good to me when I did this.
  • Next while you’re still looping and listening hold down the control key and drag the red line up and down. I dragged it really high so I could hear it really trash the audio and really low so I could hear the noise. Then I closed my eyes and dragged it until I felt I had minimal noise and minimal artifacts. Turns out I dragged it about 1dB higher than the default.
  • Use the + button to save your final results as a preset. If your room noise changes you may have to repeat the process but I’m finding my room noise has been pretty consistent for weeks and I haven’t needed a new profile.

  • After I had a noise filter I liked, I  added a noise gate to my FX chain. I wasn’t able to detect when the gate kicked in and out but all the low level breath sounds and noises were gone. When I turned the gate off I could hear some mild artifacts on my breathing but since the gate eliminated this I didn’t really care. 

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    About Me

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    Tod Gentille (@todgentille) is now a Curriculum Director for Pluralsight. He's been programming professionally since well before you were born and was a software consultant for most of his career. He's also a father, husband, drummer, and windsurfer. He wants to be a guitar player but he just hasn't got the chops for it.