Techniques for Noise Supression in a Mix

Transcript:

In this video I’ll be demonstrating several different techniques of noise suppression. You can use these techniques if you have a problem of background noise leaking in or bleeding into your audio tracks when you’re recording. I’ll be demonstrating these techniques by using a heavily distorted electric guitar track. I’ll show you several different plugins or processing tools that can be applied specifically for noise suppression. I’m gonna go ahead and ply the guitar track so you can hear what the issue is going on. Before the guitar even starts playing, you’ll hear some background noise that’s just being generating by the electric guitar amp.

[electric guitar]

One thing you could do if you’ve recorded in Pro Tools or any other DAW, is go in and find the parts where the guitar is not playing, and go in and did those things out — and cut them out.

However, depending on your guitar track, for instance here I have in the performance the guitarist playing and then stops playing, and then plays again and then stops playing. This would take a long time to edit out each of these tasks. So you can actually use a plugin to kind of automate this process for you. This is called the gate or in other terms even called a noise gate, specifically because you can apply to — cut out or eliminate the noise that leaks in on a track, and that’s what I’m gonna be doing here.

The idea is the quiet signals are going to be reduced in volume, and that’s the purpose of the gate. So you would hope that the noise is actually quieter than the actual signal that you’ve recorded. In that case you can actually use the gate to turn down the parts from the noise that are quiet but then allow the signal part where the guitars actually playing to pass through.

So I’ve got it set up right now with a pretty fast attack, medium release and hold, so that when the guitar is playing, the gate is allowing the signal to go through, but when the guitar is not playing it’s cutting the signal out. You’ll notice here at the beginning, the noise has basically been eliminated up until the time when the gate starts — or the guitar starts.

[distorted guitar]

Sometimes when you use a plugin like this, it’s actually difficult for the gate to a anticipate when it should turn on and turn off. And this plugin, this is the stock pro tools gate, has lookahead feature that kind of helps out with that.

I’m gonna show you another technique now — that you can actually control how much the gate can essentially look ahead at the signal to figure out when it needs to open and when it needs to close. And the way to do this is to actually duplicate the guitar track and use it as a sidechain.

So, what I’m gonna do if I zoom in now at the beginning of my guitar track, is I’ve actually offset a duplicate, I’ve muted it, I’m not gonna be actually listening back to it. I’ve duplicated this and actually dragged it a little bit forward so that my duplicate track that I’m gonna side chain my gate with, is a little bit in front of the actual guitar track. This is gonna tell the gate to turn on a little bit before and open up so that the signal can pass through rather than have to wait for this signal to get loud. You might have the issue that it cuts off a little at the beginning when the guitar is playing. This way the gate opens up and makes sure that all the signal when the guitar starts is passing through.

So let me show you exactly what I’ve got going on. I’ve created a second version of the same plugin. And this time, what I’m doing is sending some of the signal over here from the duplicated track. Sending it pre so I can turn down the volume here and I’m not hearing the output. I can send this signal over here through the key input or the sidechain input to my gate, listen to the side-chain. I have to have a little bit of a longer release, and hold, so that I make sure I’m not cutting off at the end. And it sounds like this then.

[guitar]

So you can hear, I’ve definitely suppressed the sound at the beginning. Next it’s just a matter of figuring out exactly how you want this duplicated track to line up. You can shift it more forward or more back so that the offset essentially just allows the guitar to come through and doesn’t cut off too much at the beginning but it also doesn’t allow too much noise at the beginning. So that’s the trade off to be aware of.

Let me show you a couple other tools that can be used. Depending on the type of noise that you have, sometimes it’s actually better to use an equalizer plugin. So in this case I’m gonna bring up the Waves Q10. I’m only using a signal band and let me show you how you can use this, sometimes if your noise is very focused at a particular frequency you can use a plugin like this to actually cut out the noise. So if I show you here at the beginning, just the noise. What I’ve tried to do is find the particular frequency where the noise is louder, use a very sharp Q, so I’m just pulling out that frequency, I can turn the noise down. This works better for things like hum and buzz, but in some cases if you have noise like this I can find just the one or two freuqneices that are particularly bad and cut them out. So this is another thing that you frequencies try depending on the noise that you’re encountering.

Next let me bring up some other plugins, this is the Waves NS-1. Essentially the way that it works it’s a very simple plugin to use so that’s probably one of the better things about it. You just have this slider that you can suppress noise and listen to what it sounds like now as soon as the guitar starts playing.

[distorted guitar]

One of the advantages of a plugin like this compared to just using a noise gate, is a noise gate is only cutting down the noise while the guitar is not playing, while the signal is quiet. A plugin like this, the NS1, is detecting noise here at the beginning and then actually eliminating that noise even while the guitar is playing. And so, not only are you just eliminating noise here, but you’re also eliminating the noise while the guitar is playing. You have to be careful though, if you turn the slider up too much, it’s gonna be eliminating noise while the guitar is playing, but it could also be eliminating part of that guitar signal which you don’t wanna do. You mostly just want to pull out the noise and leave the guitar signal intact.

So the NS-1 is probably the most simple version of this sort of thing. But Waves has several other noise suppression plugins that can be applied. The W43 is actually a more complex version of the same thing. You basically have the sliders and different frequency bands. It’s just a matter of pulling out the noise that you like in each of the frequency bands so if you know that your noise is more in the high-mids, you can just pull down the noise in the high kids, but you don’t have to worry about pulling down the signal in the lows or the low-mids. Wherever you find that the noise is, that’s where you can take it out. This is gonna cut down on the issue that you can have with the NS1, where if you’re cutting out signal during the — when the guitar is actually playing — you have the issue that it could be pulling out more of the actual guitar signal, not just noise. Here you can focus on different frequency bands and just pull those out.

[guitar]

Next up is another plugin from Waves. They all just have different featured and sound a little bit different. This one is the WNS. One thing about that is it will actually suggest the frequency ranges or how you want to set the plugin to cut out the noise. So if I play this back here at the beginning and allow the plugin to listen to the noise, it will kind of figure out where the noise is and where it needs to be removed.

[guitar]

Then it’s just a matter of playing the track back. And you still have control after the fact if you decide that you want to pull more of the noise out, you can always do that. You just have to worry bout the idea of sucking the tone out of your guitar signal too with this plugin. So it’s a subtle thing and it’s kind of a balance between how much noise you pull out and you have to worry about the issue of also pulling out the sound of the signal.

Next up is the X-Noise from Waves. It also has this adaptive process where it can listen to your track, and figure out what it wants to remove. So if I highlight the noise at the beginning, and let the plugin listen to it. Now the plugin has figured out the noise that it wants to remove and so you can listen to what the output of the plugin or what it’s actually listening to or removing the noise. Here’s the noise that it’s taking out. And the actual audio of the signal. So if I playback the guitar now, you’ll hear that the noise has been removed. This is the part that the plugin is thinking is noise. So it’s removing noise even during the guitar signal, which is cool.

Last up is the Z-Noise from Waves, has a similar functionality to the X-Noise is just even a little bit more complex. Next up if I play back the audio track.

[distorted guitar]

One thing you do have to be careful of, especially with some of these more complex algorithms for noise reduction, is there can be a fair amount of delay or latency that these plugins impose on your audio track. So you just have to watch out for that and then compensate for it. And that’s all the plugins I was gonna demonstrate. Hopefully this gave you guys some ideas about different things and techniques you can use for reducing the background noise that can sometimes leak into your audio tracks.

Eric Tarr

Eric Tarr

Eric Tarr is a musician, audio engineer, and producer based in Columbus, Ohio. Currently a Professor of Audio Engineering Technology at Belmont University in Nashville, TN.
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