In the realm of audio recording and production, achieving pristine sound quality is the ultimate pursuit. Despite this, throughout the vast array of recording environments and the various types of equipment used to capture audio, unwanted noise can become a challenge. The good news is that there are a number of techniques engineers use everyday to reduce noise for crisper audio — both at the source, and in post-production or mix-down. Utilizing such techniques, as we’ll describe, can ensure the clarity of your recording projects and bolster your toolset to a point where the frustration of unwanted noise becomes a thing of the past. Read on for noise reduction techniques that will help you achieve crisp, clear audio.
Noise Levels
Sound pressure, or acoustic energy, of which all sound (including noise!) is composed, is measured by two primary values: amplitude and frequency.
- Amplitude refers to the actual volume, in decibels (dB), of a sound.
- Frequency refers to the pitch of a sound, measured in hertz (abbreviated Hz; also known as cycles per second).
There are several kinds of decibel scales used as references to measure the amplitude of a sound. The one that most accurately corresponds to the broad spectrum of human hearing, defined and standardized by the International Electrotechnical Commission (IEC), is called the A-scale, or A-weighting.
For example, the average spoken voice is around 65 dBA in amplitude, while a loud concert may be as many as 120 dBA. Decibels are measured logarithmically, so a volume of 60 dBA does not mean “half as loud” as 120 dBA.
Types of Noise
The types of noise audio engineers encounter on a regular basis fall into two broad categories: background noise and electrical noise.
Background noise consists of any sort of ambient sound that can creep into a recording, especially in a room that hasn’t been acoustically treated. Recording at home, in an untreated space, you might pick up the birds chirping outside or cars driving down the street. Low-end rumble is another common form of background noise.
Electrical noise comes from your audio equipment. It presents itself in the form of hum, hiss, crackle, or buzz. If you’ve ever played a loud guitar amplifier, you’ll have noticed an inherent hiss from the speakers when you’re not playing. Analog outboard equipment, such as preamplifiers and compressors, might also introduce noise to the recorded signal. An additional common form of electrical noise is the infamous “60-cycle hum,” which is a humming sound caused by a ground loop, or originating from an electrical outlet. 60 cycles, or 60 Hz, refers to the pitch of the hum.
Why it’s Important to Reduce Background Noise
Unfortunately, unwanted noise has the power to ruin a recording if we’re unsure of how to minimize it. Background noise requires diligence to isolate the sound source and use proper microphone technique. When recording in a professional studio, tremendous effort has gone into designing and acoustically treating the control room, live room(s), and vocal booth(s) to create an acoustically isolated space. This ensures minimal, if any, background noise.
Electrical noise can be fickle. In some cases it’s quiet enough to be unnoticeable in a dense mix. Sometimes the volume of the instrument or voice itself drowns it out. That’s called having a good signal-to-noise ratio. This is when the amplitude of the signal is greater than the inherent electrical noise produced by our recording system.
Thankfully, digital recording is significantly quieter than tape, so we no longer need to “print hot” to drown out a humming large-format console, buzzing outboard equipment, and a hissing tape machine. When all else fails, there are software plugins dedicated to removing noise from a recording!
How to Reduce Ambient Noise
Reducing ambient noise is mostly a matter of finding a quiet, isolated place to record. This can be a challenge at home, especially if we don’t have a dedicated studio space to work with.
Choose the Right Location
Some general guidelines are to choose rooms with the least amount of echo, or reverb. You want a dry, isolated recording that serves as a clean slate come time to mix. Bedrooms or highly furnished and/or carpeted areas tend to work well. Big, dense pieces of furniture like beds and sofas can absorb unwanted reflections.
People frequently record vocals in their closet for isolation. Although, do note that recording in too small or too dead of a space can sometimes lend an unnatural quality to the recording. It’s important to find a balance between deadness (zero to very minimal echo) and liveliness (openness and naturalness).
Turn Off Appliances
When you’ve found an appropriate place to record, make sure to turn off any noisy appliances such as air conditioning or fans. Even computer fans can make their way into a recording if they’re loud enough. Anything you can do to reduce ambient noise before recording will ensure a crisp audio capture.
Choose the Right Mic
Going a step further, using microphones with a directional pickup pattern helps minimize ambient noise as well. The most common polar pattern is cardioid, which captures sound directly in front of it (on-axis sound). It rejects sound from the back and sides (off-axis sound).
Use a Filter
Finally, you can invest in a simple, but effective reflection filter: like this one by sE Electronics. These attach to a microphone stand and create an isolating semi-circular filter around your mic. Reflection filters often consist of several layers of acoustically absorptive material. The sound entering the microphone is then absorbed and diffused before it has a chance to reflect off of a hard surface and back into the microphone. It helps to reduce echo as well as comb filtering.
Best Mics for Noise Reduction
Shure SM7B Cardioid Dynamic Studio Vocal Microphone
The Shure SM7B is one of the most well known microphones in the world. This dynamic cardioid mic is continuously trusted for voiceover, broadcast, and vocals thanks to its wide, flat frequency response and crisp reproduction of music and speech. Internally, it incorporates heavy-duty shielding to reduce electromagnetic noise — particularly that caused by computer monitors and other electronic equipment frequently found in studios and content creation stations. The SM7B also features a large built-in pop filter and windscreen to minimize the impact of plosives. Its cardioid polar pattern does an excellent job of rejecting off-axis noise and ambience.
As a dynamic microphone, the Shure SM7B requires a hefty amount of gain to drive. Most entry-level interfaces have enough on tap, and many digital preamps are quite clean, even when being pushed hard. However, the chance of inadvertently increasing noise levels by pushing a preamp too hard is still present. This is why the SM7B is frequently paired with an in-line gain boost such as the CL-1 Cloudlifter.
Audio-Technica AT2020USB-X Cardioid Condenser USB Microphone
Audio-Technica’s AT2020 is a popular cardioid condenser among content creators, streamers, and music producers. The XLR version has been a favorite for years because of its affordability and sound quality, while the latest USB-C model offers plug-and-play connectivity for instant amplification.
Directional cardioid pickup focuses the sound source and does an admirable job of rejecting off-axis noise and room ambience. Being a condenser microphone, it’s quite sensitive and able to reproduce sound with precision, nuance, and detail, while still keeping excess noise to a minimum. The AT2020USB-X has its own headphone output and mix control. Therefore, you can monitor your voice alongside any audio coming from your computer. This microphone is an all-in-one solution for creators.
Neumann TLM 102 Condenser Cardioid Microphone
The Neumann brand has been synonymous with high fidelity professional recording for decades. Their most ubiquitous offering, the U87, can be heard on countless hit records going all the way back to its inception in 1967. The TLM 102 is a more affordable way to bring Neumann prestige to your home or project studio.
This microphone is a large-diaphragm cardioid condenser with a mostly flat frequency response up to 6 kHz. From 6k and beyond, there’s a gentle presence lift for crystal clear, sparkling capture of various instruments and sound sources. The TLM 102 makes an excellent vocal microphone, though it excels as a studio workhorse, too. It’s able to tolerate sound pressure levels of up to 144 dB without distortion, for noise-free recording of virtually any instrument imaginable.
Rode VideoMic NTG On-Camera Supercardioid Shotgun Microphone
For video creators, few microphones compare to the flexibility and quality of the Rode VideoMic. This handy shotgun microphone effortlessly mounts to a camera and connects via 3.5mm for seamless capture of picture and hi-fi audio. In terms of noise reduction, its supercardioid polar pattern is incredibly tight. This is one of the most “point and shoot” pickup patterns available, with exceptional off-axis rejection. To take it a step farther, the VideoMic ships with a foam windscreen to ensure maximum protection when shooting outdoors or in noisier indoor environments.
Basic Noise Reduction Techniques
Engineers have a lot of tricks and tools at their disposal to reduce noise. One of the simplest and most common is the noise gate — a dynamics processor that opens and closes in response to an input signal and a user-set threshold. The noise gate has the ability to close, or mute, a signal, and re-open once that signal surpasses the threshold. It’s useful on electric guitar, kick drum, and other sources where there may be extraneous noise or room ambience. On kick drum, for example, you can set a noise gate to only open when the kick plays, effectively muting bleed from the rest of the drum kit. On guitar, you can eliminate amplifier hum or buzz whenever the guitarist is not playing. Noise gates play a major role in both live sound and studio mixing as a quick means of fighting everyday noise and bleed.
In numerous other instances, a mixing engineer has to work with audio they haven’t recorded themselves. Depending on how or where the audio was recorded, there’s a good chance unwanted noise has made its way into the recordings.
Engineers frequently rely on restoration plugins, like iZotope RX, to intelligently remove hiss, hum, crackle, buzz, pops, and other noises that degrade overall audio fidelity. Software has made previously impossible tasks possible with its ability to remove noise and restore quality. Archival engineers, who are required to digitize and maintain old tapes and recordings, frequently employ high-tech noise reduction software to perform their jobs.
Conclusion
As we come to a close on noise reduction techniques for crisp audio, it’s important to note that while very effective, they should be used judiciously to avoid over-processing the audio. Striking the right balance between noise reduction and preserving the natural quality of the audio is key to achieving a clean, crisp, professional sound. On the front end, there’s much to be done in order to reduce ambient noise, beginning with the room itself. On the back end, we have noise-reducing plugins to help us get rid of electrical nuisances that may have made their way into our recordings.
Featured image by Troy T on Unsplash
