This is the first post in a series that will examine the basics of audio production. Any one of these topics could be examined in depth over several articles, but I feel that painting in broad strokes is a good starting point. More technical discussion can follow.
What Noise Gates Do and Why They Make Life Better
A podcast is an excellent setting for demonstrating why a noise gate can be useful tool. As I mentioned in the previous post about podcast syncing, it can be useful to have separate tracks for individual contributors. A noise gate is a tool used to fix a common problem, specifically, background noise. We’ll start with the problem and follow up with how noise gates address it.
Three podcasters have recorded a show and sent you their individual files. After studiously syncing up the tracks and performing the final mixdown, all you hear is noise, noise, noise. Where did it all come from? Skimming through each of the tracks, the problems become readily apparent.
Podcaster A placed his mic right next to his high-powered, multi-fan gaming rig. His computer is cool, but his track is awash with fan noise. Podcaster B left his windows open, allowing the general background noise of the neighborhood to be included with his file. Podcaster C forgot to close his office door while his wife happened to be watching Law and Order: Special Victims Unit: Miami: Academy Squad. Put all of those noise sources together, and you have the recipe for a distracting cacophony of unpleasantness.
The only information we are interested in is the speech of each panelist. Everything in between is extraneous and distracting information. We could go through each track and mute all of the non-speech sections of the file. That’s tedious work, however, and podcast editors are a busy group of people – we have Ferraris to drive and yachts to polish. If only there was a tool that could get rid of all that background noise for us automatically!
Enter the Noise Gate. This is a tool that allows the user to set a volume level as a threshold. Anything below that threshold is gotten rid of. Everything above that threshold is left alone. With the proper setup, a noise gate can solve noise issues quickly and easily. Let’s look at an example:
Here we can see the aforementioned fan noise, as well the speech we are trying to retain. I’ve inserted a blue line that will serve as our threshold. Note that it skates along just above the noise, but is well below the volume of speech. As I mentioned above, once we apply the effect, everything below the threshold will be removed, and everything above the threshold will be left alone. That means that the important part, the speech, will remain.
Here’s a picture of the same region after the effect has been applied. You can see that the noise has been removed, but the rest of the track is unaffected.
I only highlighted a small section of the track and applied the effect, so you can see at the left and right side where the noise comes back in. In between, the sections that only contained noise have been removed, and our noise problems have been solved.
Some of the more observant among you are thinking that the noise will still be present when the person is actually talking. This is true. However, the signal-to-noise ratio will be great enough that it will not be as noticeable to the listener, and that noise will not be compounded by the noise on every other track as we’ll be applying the same effect to everyone.
Who else can benefit from a noise gate? Guitarists are a good example. With high-gain amplifiers getting louder and louder, all of the background noise from the pickups to the amp are made louder as well. While the guitarist is playing it’s not an issue, but in between there is nothing to be heard but buzzes, hum, and crackling. A noise gate can clamp down all of that extra noise until the player starts up again.
Things to Watch For
One drawback to a noise gate is that, if set too aggressively, it can start impacting that content that you are trying to preserve. If you have a panelist who is a perpetual mumbler, for example, you might notice him or her trailing off at the ends of his sentences. His speech volume can dip precariously low to the threshold line I drew above, and his sentences will fade away to nothingness more than they already do. Because of this, I like to apply a noise gate after I’ve done any dynamic range adjustments such as compression or limiting.
Another note is that the utility of a noise gate diminishes drastically if used after mixdown. When all of files have been combined, a gate will only kick in when no one is talking. At all other times, the gate will be “off”, meaning all of the background noise is left in. As such, I’ll leave the noise gate as an online effect that gets applied at the same time as mixdown, meaning it’s the last thing to happen to each individual track before they are combined.
Conclusion and Further Reading
A noise gate is a useful tool that can solve noise headaches that plague amateur recordings. Most studios strive to be as quiet as possible to avoid having to solve such issues in the first place, but the real world is full of noise that is beyond our control. Gates provide a fast and easy way to eliminate or reduce background so that the focus can come back to the important information that we are trying to convey.
Noise Gates at Wikipedia