Noise has always been the enemy of audio recording. When digital recording became dominant, many of us thought noise was in the past. Sure, we got rid of tape hiss and others kinds of analog noise, but in the digital world we still have noise left. Here are some of the culprits.
One of the reasons we hear noise in digital recordings is because the recording itself is now so quiet. Recorders with 24-bit resolution are so quiet these days that any noise in the recording chain is magnified. We've all had favorite pieces of vintage outboard gear that used to sound great later develop hums and buzz when used with a very quiet digital system. The noise was always there. We just never heard it before.
To zap noise, we have to examine every part of the recording chain — from microphones, preamps, processing gear to recorder. Every dB of noise can add up and multiply with a larger number of tracks. The source must be isolated.
Begin with mics and look at a spec that is often overlooked or ignored by manufacturers. That is self-noise. Usually A-weighted in the specs, self-noise reveals how much output a microphone produces from a sound at a specific number of dB SPL. Large-diaphragm mics usually have lower self noise than small-diaphragm condenser mics. Buy mics with as low self-noise as possible. Mics under $300 can be found with a self-noise spec of 5 dB (A-weighted). Don’t buy studio mics with with a self-noise of over 22dB.
Self-noise of microphones matters more for voice and acoustic music recording. It is less important for loud rock music, which tends to cover up the noise. Also note that lavalier mics tend to have more self-noise than studio mics. More expensive lavs tend to have lower self-noise than low-cost ones.
Moving to mic preamps, most of today’s good quality mic preamps are low in noise. Modern solid-state preamps tend to be quieter than tube preamps. In preamps, the way the device colors sound may be more important to some users than noise. But users should be aware of the tradeoffs that vintage gear adds more noise. Needless to say, outboard compressors, EQ and other processing devices can also add noise, especially with vintage gear. An alternative might be emulation plugins of vintage gear.
When using mixer hardware for multiple channels, avoid cheap, no-name gear. Buy the best that you can afford. Make sure all mixer channels not being used are muted during recordings. Unmuted channels are a source of noise. Use proper gain-staging to keep signal levels up. This will help reduce noise levels.
Another source of noise can be cables. Use the best quality cables available to tie components together. Cheap cables and connectors are a good place for noise generation. Use a professional contact cleaner on mic and line jacks and patch cord plug contacts. Also treat control knobs. The surfaces of dissimilar metals can crystallize and turn into RFI. This cleaning treatment helps protect against minute crackles that can hide during the recordings and be revealed in the final master.
Another way to find noise in any system is to properly treat the recording space with acoustical treatment material. Then listen. Once a space is silent, noise tends to jump out. If the room is noisy to begin with, it is often hard to hear noise in the gear. With voiceovers in less than desirable spaces, try a Reflexion filter. These can improve vocals and remove the results of room reflection. For very low-cost home studios, record in or near a closet. Clothes help diffuse and absorb sound. A couple of panels of acoustic treatment can aid this even more.
Sometimes — despite all our efforts — noise cannot be avoided, especially when working on location. iZotrope’s RX7 can help remove noise, clipping, clicks, room rumble and other things that creep into the sound. The widely used RX7 is available in basic and advanced versions to handle a wide range of noise issues. But it is only for use when disaster strikes. It always best to avoid these problems to begin with by using your head to sort through the noise issues.
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