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I just recorded with a shure mic & a focusrite amp. I recorded it in my vocal booth. But for some reason there is a very irritating low hum, during the recorded - listen to the recording here - http://vocaroo.com/i/s0cDSoXQUCYU

if you listen carefully there is a low hum, which is noticeable with good headphones on. How do I remove it? any advice

Thanks

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There are enough patches in the recording with the hum and without the voice to use a noise removal tool -- Audacity has one built in and the LADSPA plugins provide this kind of thing. I'd be shocked if the likes of Protools, Logic etc didn't have such a thing. As the comment mentions below, the noise is sampled and then its audio spectrum removed from the FFT of the sound.

For future, you may actually find it quicker to resolve the cause of the hum (which is probably due to an earth inconsistency with the recording equipment, although it sounds to me more like a cable that's been unplugged so maybe a channel open which shouldn't have been, or you're not using a balanced cable run in which case you can forget about getting a decent signal) and then re-record, depending on how much time things take.

  • That's not quite how FIR denoising works... you can't "apply the reverse to cancel", since noise is stochastic (i.e. you don't know the phase). It actually works by subtracting the noise's frequency spectrum (without phase information) from the signal's FT, then converting it back to time space. This can sometimes work excellently, but sometimes the artifacts are more annoying than a simple traditional gate. — +1 for unbalanced cable etc.: it's definitely better to fix the problem's source rather than mingling in post-processing. – leftaroundabout Nov 29 '14 at 18:18
  • You know, I was actually wondering that as I was writing this post -- you're right @leftaroundabout – David Boshton Dec 2 '14 at 12:47
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You choose when to stop,

Original file (as downloaded from Vocaroo)

First, a cut at 8 kHz...

Remove hum at 8 kHz

Audio after 8 kHz cut

Next, a 70 Hz high-pass...

70 Hz high-pass

Audio after 8 kHz cut and 70 Hz high-pass

And just for fun a pass of iZotope's "Dialogue Denoiser" (auto setting)...

Audio after 8 kHz cut, 70 Hz high-pass, and Dialogue Denoiser

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