Noise Reduction For Clean Audio

Your Mic hears more than you do. You may not like everything it hears though.

The success of a piece of audio, like any creative endeavor, is determined by the sum of its parts. Background noise that contaminates audio where a clean sound was intended can be distracting and detract from the effectiveness of an otherwise worthy piece of audio.

What is noise? Noise can most loosely be described as any sound that is unwanted or detracts from our intent. To this day there are parents around the world who think that all metal, rock and punk music was produced by the same band; “Turn That Noise Off!” The point is that in our everyday life, like our tastes in music, noise is completely subjective. Noise in a recording situation is a little more objective. Our brains are unbelievable processors of our aural experience and can edit out peripheral noise so that we can focus on what needs to be heard. That’s how we can maintain a conversation in a loud café or on a street with enormous screeching trucks and cars whizzing by. A microphone is different. A microphone will not edit itself, its job is not to make a decision as to what noise is. Its job is to capture all variation of sound levels and sound frequencies without prejudice. A microphone to audio is what a camera is to light. It will hear everything it is designed to hear. A camera though, has the benefit of being able to look in only one direction (OK, mics sort of can too, but that discussion warrants another article altogether).

One of the terms most commonly used to describe aspects of a recording is the “signal to noise ratio”. We will use a very simple explanation of this for our purposes. Signal is the sound we are trying to capture. Noise is the stuff we don’t want in our recording. The higher the ratio between these two aspects of our recording the more successful we have been in achieving our goals. To a recording professional, signal to noise has a more specific meaning beyond the scope of this article.

Within this loose definition, we can categorize it further: Some of the noise is environmental — it is part of the soundscape you are recording. In some cases, environmental noise can easily be eliminated by practicing good recording techniques. Other noise is introduced by the equipment itself — this noise is often more difficult to deal with but as often is the case, this noise can be controlled by throwing more money at the problem.

With audio we are trying to communicate an idea, just like any other medium. Anything that detracts from that idea is worth trying to get rid of. Noise that finds itself between the intended idea and your ears is the quickest way to distract from the impact of that idea. In the category of environmental noise, an example of this might be: the level of the vocal you are recording (signal) to the kids playing loudly in the next room (noise). The ideal signal to noise ratio in this scenario would be high levels of vocal and no levels of loud children.

In these examples, either equipment generated noise (a poorly grounded microphone cable introducing a hiss or buzz into the signal chain) or ambient background noise (those kids) competes with what should be the featured sounds. To overcome this, we would strive to have the signal of the instrument be at levels much higher than the noise in the background or generated by our equipment.

Virtually all recording equipment generates noise, but it’s easiest to hear in entry level equipment as low frequency static, humming, pops, clicks etc. There are no shortage of reasons that gear can give us problems: cheap components, poor assembly, dirty power (power that has inconsistent intensity, which doesn’t sound “smooth”) are just a few of the things that can sabotage our recordings. Furthermore, each piece of equipment that is chained together will have a compounding effect on noise. If you choose to let one piece of noisy gear into that chain it may undermine the integrity of the whole process. With audio equipment the old adage rings true, you get what you pay for.

As we’ve seen, each stage in your process introduces noise, from the initial choice of your recording environment to the output at mastering stage. The best chance of eliminating it is at the point in time at which noise is polluting your recording process. If a piece of gear, traffic noise or kids in the next room are making noise before you hit record it will be on the resulting recording. We’ve discussed this in relation to gear and people’s potential effect on a recording environment, now let’s take a look at how it can apply to the environment itself.

Sometimes just listening to your environment with purpose will be enough to have you hear the clicking ceiling fan and turn it off. Or to turn off the faucet pouring into the tub, which is close to overflowing. While you’re in the bathroom, turning off the water, take the opportunity to clap your hands. Listen to the sound that follows each clap. You may hear a laser type buzzing or a high frequency humming type sound. However you describe it, that’s the same sound that busts you for talking on the phone to your friends while doing your business. This is actually the natural reverb of the room. Energy from a sound impulse or signal (clapping hands) is sent out in all different directions. Some of this sound energy gets caught bouncing back and forth between two parallel surfaces (walls). Unfortunately every time it passes your ears, or a microphone, it is heard or recorded over and over again. Also as these sounds bounce back and forth they begin to join forces and add harmonics or color to the original impulse tone. These phenomena are known as standing waves and give a very specific tone to audio recorded in a bathroom. In most situations this specific tone is interpreted as noise. It becomes quite a challenge to sit these recordings against other audio material and maintain a sonic continuity. They will work for the odd Jim Morrison track but for the most part, sounds made in the bathroom should stay in the bathroom. It may sound interesting alone or as a small effect in a mix. But start stacking too many tracks of this nature and you begin to get a muddy noisy mix. Lets do a few things to change our recording environment in the aim of controlling these standing waves and producing higher quality audio content.

This is a great little set up to help control unwanted reflective/standing noise. Find your mom/wife/husband/roommate’s thickest most plush blankets (the thicker the better). Hang them 6 to twelve inches off the walls in a corner on both walls. What the heck, they’re not your blankets — use a couple for each wall. Utility spring clamps from a hardware store are relatively inexpensive and do nicely to help facilitate this process. If there’s no carpet, throw a blanket or rug on the floor in the same corner. This will help with the sound that is reverberating between the ceiling and the floor. Use a cardioid pattern microphone (more about mics at a later date) on a stand with the cardioid pattern directed right into the corner. Between the back end cancellation of the mic pattern and the absorption quality of your blankets you will reduce the amount of unwanted noise in your recording. And you’ll have a great place to sleep when you are finished those all night sessions. If you are a bedroom producer, here is a similar MacGyver type technique to use. A closet full of clothes is a low reflective space that can be used to capture close relation audio ie. vocals or small instrumentation. We know a guy who opens his closet doors, hangs blankets off and over the doors and directs a cardioid pattern into the closet to record dialogue and voiceovers. The resulting recordings are low in extraneous room noise and are very workable for the engineers that end up applying them to projects. Whatever technique you use, the same or similar will give you better results than a bare room. Remember our goal: a high signal of the content (good) compared to a low level of noise (bad).

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