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Q. How can I remove background noise from a voice recording?

By Mike Senior

I've made a recording of someone talking, but there's quite a lot of background noise. How can I extract the vocals, or at least bring them out a bit to make them clearer?

Katy Majewski via email

SOS contributor Mike Senior replies: Assuming that the voice you've recorded is destined to be heard on its own, any kind of normal full‑band dynamics process, such as the expansion or gating you might use at mixdown, will almost certainly be too blunt a tool for the job. All they'll do is restrict the noise only to those moments when the voice is actually speaking, which won't help make the voice itself come through any clearer.

In the first instance, I'd therefore recommend a dedicated multi‑band noise‑suppression algorithm instead: something like the Cockos ReaFIR plug‑in (part of their freeware ReaPlugs bundle) or Voxengo's ReduNoise would be a good first port of call. These work by analysing a section of the recording where the vocal isn't present, in order to build a profile of the noise signal, which can then be used to remove the noise more intelligently. The settings of these plug‑ins can seem a little intimidating, so you'll have to get your manual‑reading cap on, but they're capable of pretty good results in the right circumstances. One tip here, though: when you first try this process, dial up the noise reduction to its most severe so that you get familiar with the strange little digital chirping artifacts it can cause. That way, when you're actually trying to decide on the best compromise between the levels of noise‑reduction and processing artifacts, you'll know what to listen for.The ReaFIR plug‑in within Cockos' freeware ReaPlugs bundle can be used to reduce background noise in a more transparent way than is possible using ordinary expansion or gating processes.

If this doesn't do the job adequately, and the recording in question is an important one for you, it's probably time to call in the professionals, and in this regard I'd personally recommend giving CEDAR Audio (www.cedar‑ a call. They've been at the forefront of this kind of technology for years, and run a by‑the‑hour restoration service that is comparatively affordable, bearing in mind the cost of the processors they use!  

Published April 2011