Noise Reducing Percussion Samples

A quick tech ‘how to’ post today… around noise reduction in live-recorded samples.  As I’ve mentioned previously, I use a lot of live recorded sounds in my tracks, especially live recorded percussive sounds.  Sometimes these sounds can be recorded quietly in the studio, but other times I capture them ‘on location’, and hence have to work with background noise.  On other occasions the background noise is unavoidably entwined with the sound source.  This was the case today when I recorded some tom sounds from the Volca Beats speaker.  The direct sound from this Volca is fairly useable , but the speaker is really hissy, and hence I ended up with a lot of hiss in the sample…

The raw sample

In the past I used to try and remove this in one of two ways…

  1. Use a high shelf filter to reduce the hiss
  2. Use a gate to fade out the tail of the sample

…but neither of these were ideal… the filter option would remove high frequency content from the whole sample including the attack part (which can significantly alter the sound).  The gate avoids that problem, but requires that you find a trade off between cutting the low frequency content of the tail (using a short release time), and ending up with audible hiss remaining in the tail (using a longer release time).

But, using automation you can combine the above approaches and get a much better result than either in isolation.  The trick is to use a high shelf filter, but automate the gain/level control, so that it’s very quickly attenuated just after the attack of the sound is finished.  The screens below demonstrate the setup in Reaper.  First you import the sample into an empty track.  Then add a high shelf filter into the FX chain (I’m using Reaper’s built-in ‘ReaEQ’ below to keep things simple).  Then automate the gain/level control of the filter (using the ‘Track Envelopes/Automation’ button on the track control)…

noise-reducing-percussion-samples-1
Reaper track ‘Envelopes/Automation’ window

Then draw an automation curve as shown in the below screen…

noise-reducing-percussion-samples-2
Automation curve
noise-reducing-percussion-samples-3
ReaEQ settings (‘Gain’ is controlled by the automation)

Depending on the nature of the sample, you’ll want to try adjusting the 4 highlighted parameters above to get the noise-reduced version sounding right…

  • The point where the filter starts to drop
  • The time the filter takes to get to minimum gain, and the shape of the curve (above option is using the Reaper ‘fast start’ point shape)
  • The frequency and bandwidth/Q of the filter

If it’s an excessively noisy sample, a low pass filter might also work better than high shelf.

In this case, the same sample with the above settings turned out like this…

The ‘noise-reduced’ sample

… that’s a considerable amount of noise reduction, but has maintained all the attack and general timbre of the sound.

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