By Craig AndertonGet rid of noise, hum
Definition:
An undesired continuous signal caused by AC electrical power, typically 60/50 Hz and its harmonics., and hissDefinition:
Random noise that is inherent in electronics-based audio equipment. in your recordings—the overall sound will be so much better
Thankfully, tape hiss is in the rearview mirror for most of us. But that doesn’t mean that noise is gone completely from our lives. Now that we have gearDefinition:
Musical or performance equipment. with 24-bit resolutionDefinition:
1. (video) The measure of pixels horizontally and vertically. For example, 1920x1080 is considered HD, or high-definition. 2. (audio) The combined bit depth and sample rate of a digital audio signal. and noise floors that hit theoretical minimums, any noises are no longer covered up by something else and instead are exposed in all their ugly noisiness. So what can we do?
Well, plenty. But first, there’s no “silver bullet” for guaranteeing a noise-free recording. Every little extra dBDefinition:
1. A deciBel is a logarithmic ratio between two quantities, and is a nonlinear measurement that mimics human perception. 2. A unit expressing sound levels relative to a nominal level just audible by the average human ear, and equal to 1/10th of a Bel. 3. (slang) Database. of noise, distortionDefinition:
A change in an electronic or acoustic signal's waveform. This can undesirable if it impacts signal quality, or desirable when used for creative signal processing., or colorationDefinition:
Modification of a video signal's color. adds up, especially if you’re into using lots of tracks. The solution is to carve away noise wherever possible, no matter how minimal, to keep all those little noise bits from multiplying—so here are some proven techniques to help in your quest for quiet recordings.
Mics and Mic Preamps
Unless you get into a boutique, stratospheric price range, modern-day mic preamps (even those with relatively inexpensive interfaces and mixers) are seldom the issue with noise—concentrate on the mic itself. The Self NoiseDefinition:
The natural internal noise of a device, with no signal present. spec, which is usually A-weighted, tells how much output the mic produces from a sound at a specific number of dB SPLDefinition:
See Sound Pressure Level.. For example, RØDE’s NT1-A condenserDefinition:
An archaic term for Capacitor. mic has an extremely low Self Noise spec of 5 dB (A-weighted); it’s included in the recording-ready, NT1-A Complete bundle (Fig. 1).
Large-diaphragmDefinition:
The moving portion of a microphone that transforms sound waves into motion that can ultimately produce electrical waves. mics tend to have lower noise than small-diaphragm condenser mics, and solid-state preamps in condenser mics are usually quieter than tubeDefinition:
(slang) A vacuum tube or (valve), an electronic amplifying or rectifying element with a heating filament, in a glass or metal envelope. preamps (sorry, tube fans!). Granted, mic noise won’t be a factor if you’re using it only to captureDefinition:
To acquire audio and/or video, and convert it to a file. a track from the lead singer in the punk band Snot Puppies of Doom, but if you’re recording twelve tracks of acoustic instruments played gently, you’ll hear a difference.
Background and Ambient Noise
It’s amazing how much ambientDefinition:
1. Something in a close vicinity. 2. The natural sound of a space, or simulation of being in that space. noise creeps into a studio—which you find out only after you do acoustic treatmentDefinition:
The process of using absorption, diffusion, and other techniques to modify a room's acoustic characteristics, typically to obtain a flatter response., then walk into the room and realize that you're surrounded by silence. Although you can put up individual panels as needed, it can be more economical to bite the bullet and get a complete acoustic treatment package, like the Primacoustic London-16 (Fig. 2) or Auralex ProPanel ProKit-1. However, if money is tight, trying a 24-pack of Auralex Wedgies for spot treatment of your room’s problem areas can make a worthwhile improvement.
Unwanted Audio Other than Noise
There are other audio issues that detract from your tracks, like vocals reflecting off untreated walls, which adds a “shadow” to your vocal. sE Electronics’ Reflexion Filter (Fig. 3) can help with that because it traps your vocal before it disperses throughout a room.
Note that mic placement within the filter is important to avoid coloring the sound; you want it within the reflector’s arc, but as far as possible from the filter’s rear wall.
Another option for some home studios is if there’s a closet near where you record. All those clothes can help diffuse/absord a lot of sound, although you’ll likely still need to add acoustic treatment to the ceiling and exposed wall surfaces.
Crackles: Even Worse than Hiss
Use contact cleaner, like Caig Labs Deoxit DN5, on your patch cordDefinition:
A cable used with patch bays to route and complete electrical connection, or a short cable used to connect devices. plugs, jackDefinition:
A connector, normally female, that works in conjunction wit a plug. Usually located in a piece of equipment, or as part of a cable. contacts, and controls. Tiny crackles can be masked during the recording process by everything else that’s making noises but may show up while under scrutiny during playback. In a worst-case situation, the surfaces of dissimilar metals may have actually started to crystallize. Not only can that generate noise, but these crystals are all potential miniature crystal radios, which can turn RFIDefinition:
(Radio Frequency Interference) Interference in the proper operation of one device due to being adjacent to a source of radio-frequency electromagnetic radiation from a different device. into audio that gets pumped audio into the connection. Not good.
Human Error
Not that we make any misstakez, of course, but do make sure any unnecessary mixerDefinition:
Combiner, controller, and router for multiple audio or video signals. channels are muted when you record. Every unmuted channelDefinition:
1. In radio, television, citizen's band radio, and other wireless communications modes, a specific frequency for communication. 2. In mixers and video, an input or output signal path with controls. 3. In MIDI, one of 16 data paths. is another potential source of noise. Also, use proper gain-staging to keep signal levels up, and noise levels down.
The Heavy Artillery
No matter how hard you try, some noise is going to make it into your recorded tracks—and you’ll need to clear it up after the fact. That’s when it’s time to bring out the heavy artillery, and iZotope’s RX7 (Fig. 4) is the gold standard for noise reductionDefinition:
A technique for reducing noise in recording or transmission systems. Single-ended noise reduction systems use filtering to isolate the noise, and expand this signal downward using downward expansion. See Expansion and Downward Expansion. Double-ended systems use symmetrical compression and expansion. See Compansion., repair, and restoration software.
Even the least expensive version, RX7 Elements, can help remove noise, clippingDefinition:
Distortion caused by overdriving a signal through an electronic device, to a level beyond which no more headroom is available., and clicks, ampDefinition:
Abbreviation for either Ampere or Amplifier. hiss, room rumbleDefinition:
A noise caused by mechanical vibrations being transferred to a audio transducer, such as a turntable motor., and more. RX7 Advanced is expensive, but if you do pro-level post-production, surroundDefinition:
Multiple speakers place around a listening area to create an enveloping soundscape. work, or narration, it can be a life-saver—it can even remove lavalier mic “rustling” noises, change the intonation of dialog, and isolate dialog from noisy backgrounds. It’s basically applied magic. The middle “standard” offering, RX7-IZO, does everything Elements does but also includes features like mix rebalancing, adjusting time and pitchDefinition:
For a given range of audio frequencies, pitch represents where a single sound falls within that range., doing spectral repair (yes, you can probably remove that one cough in the middle of a liveDefinition:
Live broadcast of an event or program without substantial delay or editing. performance), and eliminate mouth clicks from narration. It’s pretty amazing.
If you plan to use noise reduction software to get rid of issues like hiss or hum, make sure you don’t edit tracks right up to the beginning or end of the audio. You want some space that’s pure noise so that the software can identify it, and subtract it from the track as a whole.
An Ounce of Prevention...
So is all this effort worth it? I think you’ll be pretty surprised when you hear what happens to a mix when the noise contributed by each track is gone. Minimizing even low-level noise can lead to a major improvement to the final sound...it’s almost like removing the dust from a fine piece of art.
