Tutorial: Fixing a Noisy Line, Part 2

In Part 1 of this tutorial, we looked at gear and line investigation techniques to try to identify and/or minimize the problem. Here, in Part 2, we will focus on software solutions to handling a noise-laden signal.

REAPER Tools
While using REAPER, I have found 2 viable options to cleaning up a noisy audio track bundled with the program itself. ReaGate, and ReaFir. We will look at both of these options in turn. But first, we need a good way to see the sound. REAPER comes with a good tool for just this purpose: "JS: Analysis/gfxspectrograph". Add this into the end of your FX Chain, and you can use it to visually monitor what is coming across on your line. Totally black means it is totally silent. You can use this to gauge the effectiveness of your cleanup methods.

ReaGate
ReaGate is the bundled VST gate that comes with REAPER. A gate is essentially an automatic on-off switch for the audio. When the overall level drops below a certain threshold, the line is silenced. Gates usually have a bunch of other features, but you probably don’t need them forthis situation. To use ReaGate, add it to your FX Chain. It should be in the top slot, before any other plug-ins are used. This will keep the other plug-ins from amplifying the noise problem.

On the left of the ReaGate interface, you have a vertical slider that measures dB (decibels). The higher you move the slider, the higher the threshold for the gate to turn off the sound. Move the slider up until the background noise disappears. For my situation, a setting of –37.8 db was the lowest point where the noise dropped off. The green bars beside the threshold reflect the incoming signal. You can watch the Output mix meter on the right hand side to see when the Gate turns the signal off.

To Gate or Not To Gate
Gates are a tricky thing. On one hand, they stop the low-level noise from coming through very well. But when you have a gate in your chain, ANY sound below that threshold will be cut off as well. So if you’re letting a guitar ring out, when it hits that threshold your sound is completely dropped out. Depending on your style of music, this clipping could sound really strange and unwanted.

ReaFir
Another option is ReaFir, with is identified as a FFT EQ+Dynamics Processor. This is a tool with quite a few modes, including a gate. The gate in this doesn’t work quite the same, and is not as effective as the standalone ReaGate, in my opinion. Change the “Mode” to “Subtract”. There will be a new check box beside it labeled “Automatically build noise profile (enable during noise)”. This feature can be your new best friend. Make sure your equipment is connected and that the track is armed, with monitoring on. If you are combating line noise, turn your instrument’s volume to zero. If your trouble is from the instrument itself, silence it as best you can with the volume at your normal recording levels. (For guitars, you can loosely tie a bandanna or other soft cloth around the neck so it mutes the strings.) You should see the noise profile pulsing in the window.

FFT Size
This setting is essentially the size of the “chunk” of data it will evaluate at a time. A smaller number means it pushes your computer harder, because it is evaluating a lot of data. A larger setting is more economical on your system resources, but it also causes a lot of latency while monitoring. Personally, I usually set mine to 512, and it is a good balance between the two.

Build A Noise Profile
Mark the check box beside the “Build a noise profile” option, and let it run for a few seconds. A red line will begin to raise from the bottom where it is detecting noise. After it stops adding to its height, click on the check box again. That’s it. You have now build a noise profile that will be applied to the audio signal passing through this VST. This is basically a frequency-reactive gate, where a traditional gate is volume-reactive.

ReaFir or ReaGate?
Both ReaFir and ReaGate suffer from the same problem with sustained audio levels. Neither one is actually removing the individual components of the noise. They are both removing the audio when there is little or no instrument audio. If you have sustained sound coming through, like you would with a rhythm guitar passage, then the noise might be evident within the sound of the guitar itself. This is because gates are trimming the quiet levels noise, but they do nothing to actually stop the individual elements of the noise. I personally prefer ReaFir's "subtract" mode to a traditional gate, because the sound doesn't just stop when it reaches a certain point. Individual frequencies do, but not the entire sound. It sounds like a more natural fade than what you get from a gate crashing down on your sound.

Other Options
Depending on your noise source, you can also investigate notch filters to try to remove individual offensive frequencies, but these will impact your overall tone significantly. In my situation, I have such a wash of noise across a lot of frequencies that it is impossible for me to take this approach.

Do you have other software tricks that you’d like to recommend? Post a comment!

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Tutorial: Fixing a Noisy Line, Part 1

Something I’ve been combating lately in my recording is line and interface noise. As I mentioned recently, the Lightsnake USB interface I’ve been using worked OK with my acoustic, but once I started recording with an electric guitar, the noise is much more prominent. There are 2 ways to correct a noisy interface: 1) Buy Better Gear, or 2) Use the tools you have to try to minimize the audible noise coming through.

Since we are about frugality, we will assume that you don’t have the scratch right now to pick up a better interface. (I’m crossing my fingers and hoping a better interface box is under the Christmas tree, or at least some cash to buy it guilt-free.) That leaves us with the duct tape and chewing gum solution (i.e. a non-ideal solution) to cleaning up your audio.

Check Your Wires
The first thing to check when you’ve got excess noise coming on your input is to check the connections. Do you get pops and crackles when you touch the cables while connected? You might have a broken wire that is adding noise when it is flexed. It might be cracked shielding in the cable that might be picking up interference. Try to eliminate as many sources of noise. And remember, an incoming audio source MUST be plugged in to something when you’re testing. A cable end dangling on the floor usually will pick up a little charge from the air, perhaps a little extra hum from finger grime on the plug ends. Also, make sure the volume on the instrument is turned all the way down. This will help you isolate whether it is the instrument’s electronics causing the noise or something with the line/interface itself. If you identify a possible broken wire, try to swap it out and see if that helps.

Check Your Gear
If you have a clean line when the instrument’s volume is turned off, then you might have a problem in your gear itself, or interference causing problems with the gear. I have found that CRT monitors will cause a little extra hum on some lines. If you can, turn off the CRT and see if the sound goes away. If this is the case, then see if you can re-route things to keep the lines further from the monitor.

Another source can be some fluorescent light fixtures. I have used a couple that will generate a lightsaber-style hum on lines nearby. Turn off the lights and see if that helps.

If you can determine that the instrument is somehow at fault, but you can’t identify anything else reacting with it, then you may want to consider borrowing someone else’s similar instrument to see if it exhibits the same problem, or take the instrument to a qualified tech and see if there are modifications you can make to reduce the noise. (For guitars, these usually either means replacing pickups, switches, or at least having the wiring re-soldered to make better connections.)

Extra Hardware
Sometimes you can isolate that it is the instrument, but there’s nothing you can do to directly fix it. There are some line filters and power filters that might be able to help fix your signal. Frankly, most of those are out of my price range, especially for a “it MIGHT fix the problem” potential solution. If you have friends with this type of extra gear, by all means borrow their equipment and see if it cures your ills. If it does, start saving your loose change to buy one for yourself. Again, this falls under the “Buy Better Gear” option, which isn’t always a viable course to take.

It’s the Interface!
In my situation, I was able to isolate it to the Lightsnake itself. As I explained in my post “Eating My Own Words”, it became more evident with the electric guitar than with the acoustic, but it is definitely the interface itself, since I don’t get the same problem with other line or microphone inputs on the same computer.

Software Solutions
If your final verdict is like mine, then the garbage on the input can’t be directly avoided without buying new hardware, so you have to try to clean up the signal after it has been received. In Part 2 of this tutorial, we will look at software solutions to this problem.

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Eating My Own Words - Lightsnake Review Updated

Well, I'll be the first to admit that having to eat your own words is not too tasty, but sometimes it is exactly what you need to do.

Recently I posted a review of the Lightsnake USB Instrument Cable. In that review, I gave it decent marks in my experience - no errant line noises like some people claimed to have heard (I even parroted the corporate "must be a bad cable" approach to people's problems.) I have once again proven to myself that you will get different results with different gear. At the time I wrote that review, I had only one guitar to try with it, a Daisy Rock Wildwood Electric/Acoustic Guitar. So my review reflect my experience with it at that time. The extra environmental noise normal with an acoustic guitar in a non-soundproofed environment caused me to always put a gate in the effects chain to clean it up. The natural fullness of sound from the acoustic guitar came across nicely and I was satisfied that the (gated) recorded material was fairly accurate to the original sound.

I recently picked up an Epiphone SG Special, which is an admittedly low-end electric guitar. Of course, I plugged it into the Lightsnake. My first reaction was "what in the heck is that racket?" The racket was, unfortunately, an electric pulsing noise over the monitors I never noticed previously (thanks to the gate). Okay, fine. I put a gate in the chain, and did some trial recording with the SG. The gate worked to take off the noise in the silent sections. But as soon as you hit anything loud and sustained (like a chord progression), the noise was embedded in the louder sections. I also tried using the ReaFIR VST in Subtraction mode to build a noise profile. Again, it works fine for trimming the noise off in silent or very light, quick notes, but if you have any continuous playing, you can hear the noise interlaced with your guitar sound.

I took a shot of a spectrograph of the line noise with the Lightsnake plugged into the SG with the volume knob set to zero. What you see is a wash of noise, with a lot of other structured pulses embedded in it. I checked old recordings from the Acoustic - I see the same "pulse signature" in the signal. I think the reason I never noticed it with the Daisy Rock on recording is that the acoustic is naturally a very full sound, so the noise was actually getting lost in the sound of the acoustic. Since the electric doesn't have the same wide-spectrum wash as the acoustic, the noisy cable is laid bare for all to see and hear.

So here I sit, eating my own words about my value shopping, and have to say I spent my money poorly. (However, I have been using it for 6 months or so before I came to that conclusion, so maybe it wasn't a total waste.) I heartily recommend saving your pennies (as I am) and save up for a more "pro" box. I'm currently looking at the Line 6 TonePort series, since it is more of a name brand with a lot more positive reviews.

Since this is the net, we can rewrite history, so I plan to. I have added the core of this post into my original Lightsnake review, so folks stumbling across it will be wiser that I was when I first wrote it.

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