timoc
Joined: 06/09/07
Posts: 114
Loc: Antwerp, Belgium
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using phase invert to remove hiss?
#864443 - 28/09/10 08:06 PM
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I've recorded a track of 5 young girls singing a capella using two AKG C1000s in ORTF
setting. The room was fairly quiet, but I had to turn up the mics a bit because, well,
girl's voices are quiet. How can I get rid of the slight hiss? Is there a free
plugin anyone can recommend? Can I measure the frequency of the hiss and cut w eq? I tried copying a slice of hiss, putting it on a parallel track and phase
inverting the hiss. It worked only for the section I sampled from. When I copy this
phase inverted hiss below the rest of the track, it does nothing to the hiss. What am I
doing wrong? Thanks
-------------------- http://soundcloud.com/carlier
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narcoman
active member
Joined: 14/08/01
Posts: 8469
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Re: using phase invert to remove hiss?
[Re: timoc]
#864454 - 28/09/10 08:28 PM
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You'll only ever be able to cancel out the exact same wave form. Hiss is invariably a
random noise wave. Look for some noise reduction plugins. Get a demo of izotopes RX.
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timoc
Joined: 06/09/07
Posts: 114
Loc: Antwerp, Belgium
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Re: using phase invert to remove hiss?
[Re: timoc]
#864471 - 28/09/10 09:14 PM
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I'm thinking maybe I should just leave the final mix quieter than I normally do.
-------------------- http://soundcloud.com/carlier
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narcoman
active member
Joined: 14/08/01
Posts: 8469
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Re: using phase invert to remove hiss?
[Re: timoc]
#864476 - 28/09/10 09:39 PM
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That doesn't change the relationship of the hiss to the mix.
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Jack Ruston
Joined: 21/12/05
Posts: 4066
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Re: using phase invert to remove hiss?
[Re: timoc]
#864479 - 28/09/10 09:53 PM
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Use a noise reduction plug in. But be careful. Noise reduction is a bit like trying to get
the fat off gravy. The more you try to remove the fat, the more gravy you end up removing
by mistake. The best compromise is to keep all the gravy and accept a little fat.
You can try reducing the level of the hiss manually in the gaps, but be aware
that if you do that too much you actually draw attention to hiss when it comes back in
with the vocals. If you leave it throughout the ear tunes it out after a bit.
J
-------------------- www.jackruston.com
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Hugh Robjohns
SOS Technical Editor
Joined: 25/07/03
Posts: 18403
Loc: Worcestershire
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Re: using phase invert to remove hiss?
[Re: timoc]
#864487 - 28/09/10 11:10 PM
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Quote timoc:
How can I get rid of
the slight hiss?
With a
noise reduction plug-in of some kind. I'd second the recommendation for Izotope RX, but
there are also good tools in Adobe Audition and no doubt there are others for the Max
platform.
Ideally, look for a noise reduction system that works with a 'noise
fingerprint' -- take a sample from part of the recording where there is just noise and use
that to 'teach' the process abut the character of the unwanted noise. Then apply the noise
reduction and adjust to erduce the noise without affecting the wanted audio.
It's very easy to get trapped into focussing too much on reducing the hiss to the
detriment of the wanted audio -- it can quickly go warbly if you're not very careful.
I'd advise restricting the hiss reduction to about 5dB or so. If you need more
than that, go for several gentle passes rather than one great big swipe at the noise!
If this is a fee-paying job it would probably be worth your while to use CEDAR's
bureaux service where they process your audio for a modest fee using the worlds best audio
restoration tools.
Quote:
Can I measure the frequency of the hiss and cut w eq?
Usually not without affecting the wanted
audio. Noise is generally a broadband signal and exists throughout the wanted audio as
well as being obvious as a high frquency hiss above it. And removeing just the HF end will
leave the audio sounding dull or boxy.
Quote:
I tried copying a slice of hiss, putting it on a parallel track
and phase inverting the hiss. It worked only for the section I sampled from.
Yes, it would. To cancel out in this
way the two audio sections have to be identical. So if you copy one section then you have
two identical tracks and they will cancel.
But noise is a randomly changing
signal, as has been explained earlier in this thread, and so your copied section won't
match any other section. Instead of cancelling, what you then have is two lots of random
noise being added together, and the hiss level will actually go up by 3dB!
hugh
--------------------
Technical Editor, Sound On Sound
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jtn191
Joined: 11/03/10
Posts: 37
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Re: using phase invert to remove hiss?
[Re: timoc]
#864823 - 29/09/10 09:15 PM
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1.+1 for Izotope Denoiser (but it's expensive)
2. Try FFT Tools (vst for mac and pc)
or ReaFir
3. Audacity has a noise removal function
The reason phase invert
doesn't work is the noise on each track isn't exactly the same down to the waveform. It's
somewhat more random, like the upper frequencies of white noise.
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pwhodges
Joined: 11/06/05
Posts: 51
Loc: Oxford, UK
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Re: using phase invert to remove hiss?
[Re: jtn191]
#864950 - 30/09/10 09:54 AM
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Quote jtn191:
1.+1 for Izotope
Denoiser (but it's expensive)
But
there's a decent special offer ($249) on the new RX v2 until the end of October. Still
plenty of money, but it challenges the best at any price.
Paul
Edited by pwhodges (30/09/10 09:54 AM)
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narcoman
active member
Joined: 14/08/01
Posts: 8469
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Re: using phase invert to remove hiss?
[Re: timoc]
#865132 - 30/09/10 10:59 PM
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.... yup. Just got it. It's very very good.
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jtn191
Joined: 11/03/10
Posts: 37
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Re: using phase invert to remove hiss?
[Re: pwhodges]
#865155 - 01/10/10 04:40 AM
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huh, Paul that is reasonable and well worth it. I was thinkin' of the Advanced version
which'd set you back 1000 bucks
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pwhodges
Joined: 11/06/05
Posts: 51
Loc: Oxford, UK
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Re: using phase invert to remove hiss?
[Re: jtn191]
#865201 - 01/10/10 09:11 AM
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If you have RX 1 basic, you can go to RX 2 Advanced for a mere $499 (+VAT here, of course)
- a real bargain that, I think.
Paul
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narcoman
active member
Joined: 14/08/01
Posts: 8469
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Re: using phase invert to remove hiss?
[Re: timoc]
#865325 - 01/10/10 02:23 PM
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indeed. Catch it while its hot !! 
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timoc
Joined: 06/09/07
Posts: 114
Loc: Antwerp, Belgium
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Re: using phase invert to remove hiss?
[Re: timoc]
#865534 - 02/10/10 10:04 PM
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Thanks for the replies. I tried Reafir, which is a pretty interesting plugin, but it very
quickly starts to affect the overall sound, creating a tunnel effect. I ended up just
leaving the hiss in and making sure as mentioned about that it didn't come in and out
during the take. You do get used to it, it's just the first couple of seconds can be
offensive.
-------------------- http://soundcloud.com/carlier
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