By Rob Stewart - JustMastering.com
Preventing and reducing noise in music production
Noise in all its forms from crackles and pops to tape hiss to air noise have been an issue for audio from the very first recording ever made. Noise can be reduced during the audio mastering process, however, I recommend controlling and reducing noise levels prior to mastering. Because noise is pervasive interference that will compete with your music for your listener's attention, it is best to address it as soon as it is found.
Why be concerned about noise in your mix?
In my view, unintentional noise will always be the number one issue for anyone who produces music. Noise is a big concern because it covers up the inner details of your music, reducing perceived dynamics. Noise robs your mix of depth, realism and purity. In today’s high resolution audio world, discerning listeners are assembling super-quiet listening rooms, purchasing high grade DACs and super low-noise amplification. These top-tier sound systems reveal all of the qualities of your mix, for better or for worse. Unfortunately, that also means painfully revealing the noise.
If you are aiming to produce high resolution audio recordings, noise must be top on your list of considerations at every step of the recording process. Failing to recognize and address noise during the production process will not only make your music sound less professional, it will also dramatically reduce or eliminate the benefit that high resolution audio technology brings to your listeners.
Fact: Noise accumulates at each step of the recording and production process
Noise is not always obvious in the early stages of the recording process, but it exists everywhere and can be captured or generated at any stage of the production process. It slowly creeps into focus as it accumulates while you work. At some point, perhaps during mixing, you may suddenly notice a hiss that did not seem as obvious to you when you were recording the first few tracks. Determining the source after you have already recorded dozens of instruments can be time consuming to say the least. Therefore, it is best to control noise while you work to prevent it from becoming a larger concern.
Sources of noise in your mix
Before I get into the different sources of noise, let's briefly discuss gain staging, an important factor in controlling noise levels. Very simply, gain staging means setting and managing the gain levels of each piece of equipment in your recording or processing chain to minimize the amount of noise in the system. Each piece of equipment you have is designed to operate best within a certain gain range. When you go above or below that range, you can introduce more noise than necessary. For example, if you set one piece of gear relatively low, and that device happens to also be a little noisy, and then feed it into another device where you have to set the gain higher than optimum to compensate, you will boost the already noisy device while adding a bit more noise because the second device is set above above its recommended operating range.
This article goes beyond gain staging (a way of managing the noise that's there), and looks a little deeper at the noise sources themselves.
Every instrument makes some kind of noise. Sometimes the noise is a part of the performance that you want to capture, but when it is not, those unintended noises you capture will pull your listener's attention away from the more important aspects of your mix. Multiply that by several tracks, and you can end up with a lot of unwanted noises in your mix ranging from breathy woodwind instruments to creaking furniture and more.
Vocal noises can be a big concern as well. Lip noises, breath noises, plosives (p-pops) and throat noises can all distract listeners away from an otherwise great performance, and as you start layering voices, those noises can build up quickly.
- Sometimes a slight change to the musician's technique can help (e.g. changing the strumming technique when playing rhythm guitar). Sometimes a different instrument helps, too. Clothing will have an impact. If the musician is wearing loose-fitting clothing it will make noise when they are playing and it will get captured by your microphones.
- Changing the angle and distance of the microphone to the instrument or vocalist can make a big difference in the type and amount of noise you capture.
- Use quality furniture that will not crack or squeak when the musician shifts their weight. Piano benches are notorious for cracking at the worst moments such as during the decay of a long held chord at the end of a take!
- If the acoustic guitar's tone is too thin, and you're hearing too much pick noise on each strum, switching to a different guitar pick will improve that. Experiment with some of the synthetic alternatives to tortoise shell, or widely available cow horn. Both of these materials tend to sound warmer than regular nylon picks.
- If the noise has already been captured, careful editing or EQ are often your best options. A carefully tuned de-esser can sometimes help percussive noise sources (for example, guitar pick sounds).
Room or environment noise
Room and environment noise (a.k.a. room tone, air noise or background noise) can come from many places. Common sources are noisy ballasts (power supplies) in fluorescent light fixtures, to the sound of the ventilation system, to roaring traffic near the building you are recording in.
- Turn off any fans, forced-air heating or cooling, and any lighting that is making noise (humming, buzzing etc.) while you are recording.
- If you use a cathode ray tube (CRT) based monitor, turn it off during recording because they can make a very high pitched whine.
- Consider moving your microphone closer to the instrument which by nature will change the ratio of instrument sound to room noise.
- Record later at times of the day when nearby traffic is likely to be lower.
- Consider sound proofing options for your room and ventilation system which while expensive, may be your best option if you are located in a very noisy area.
- If the room environment noise has already been captured, editing, gating and EQ are options. If the noise is fairly constant, noise reduction software can also help but be careful of over processing because the result will not sound natural.
Microphone self noise
Some microphone designs such as condensors or active ribbon microphones generate noise, because they have a built in amplifier that raises their output level. The design of the built in amplifier determines how much self noise the microphone creates. Cable design, length and the number of connection points also play a role.
- Choose microphones with very low self noise (high signal to noise ratios).
- Place the microphone closer to the source which will ensure that what you're capturing is further above the microphone's noise floor.
- Use high grade, balanced microphone cable. Use only as much as you need, with a minimum of connection points (use a single cable over two shorter ones connected together).
- Use editing, gating and EQ to mute the track when nothing is playing, and to EQ the tone of the noise to make it less obvious.
- Microphone self noise is a great candidate for noise reduction software because the noise is usually very constant. Just be very careful not to overdo it or the result will not sound natural.
You can occasionally run into interference, such as picking up a radio station, a buzz or a hum. Sometimes the interference is obvious but without checking for it while recording, you may only notice it when you sit down to mix.
- Pay close attention during recording to ensure you are not accidentally picking up interference. When you encounter interference, sometimes moving to a different location in the room, or turning off some electrical equipment that is causing the interference will help (turn off any incandescent lights on dimmers, or fluorescent lighting fixtures).
- To reduce the chance of accidentally capturing hum, turn off any non-essential equipment that has a transformer or external power supply.
- If you find noise in your recording and re-tracking is not an option, then processes like EQ or gating can help reduce it. There are various hum-reducing plugins available today designed to help address hum after the fact as well.
The microphone preamplifier you choose - be it the one in your console, or an outboard model - will generate its own noise which will vary greatly depending its design.
- Purchase low noise, high grade outboard microphone preamps designed for high resolution audio. There are several brands available today that offer exceptionally low noise performance. They are a significant investment, but they are your best option when preamplifier noise is a concern.
- Editing, gating, EQ and noise reduction software can help when the noise is noticed after it was recorded.
Console noise can creep into your mix during the tracking and mixing process. Some mixing consoles are noisier than others, because the level of noise varies greatly depending upon how they are designed.
- Choose a low-noise mixing console.
- Skip the console when possible. For example, during recording, go from microphone to outboard preamp, to tape or disk as much as possible.
How you use your tools, plus the tools you choose can either amplify or generate noise in your mix. For example, compression tends to increase the noise level of your mix because after applying compression to lower the louder passages of a track, make-up gain is applied to raise the gain of the track, and whatever noise was captured. Most vintage processors are noisy by today’s standards and their digital emulated versions often come with simulated noise built in.
- Be selective with the processing tools you choose. Test and analyze what the processor is doing to the signal. If it is adding noise to the signal, check to see if you can disable that "feature", and if not, I recommend avoiding it in situations where noise is a concern.
- If you are using an analog tape emulating plugin, and you wish to keep some tape hiss, consider how many tracks you use the plugin on, and then set the tape hiss level accordingly. If you are soloing a track you may not hear obvious tape hiss but on 20 tracks, the hiss will soon be very obvious.
- Process only when you need to. Remember that if you choose to process to tape, during the mix, and then on mixdown, you are adding more noise at every stage.
Analog tape noise
Having grown up with analog tape, this noise source has been high on my target list for my whole life. Tape noise is usually very obvious, and it builds up quickly. If you have 8, 16 or 24 tracks or more, that build-up of tape noise can become painfully obvious, robbing your music of depth and definition because the finer details get masked by hiss.
- Consider not using analog tape (if noise is a key concern for you, this is an easy solution!).
- If you prefer to use use analog tape, use a brand new tape to capture your recording. You will achieve the best sound quality by using a brand new tape.
- To help minimize tape hiss, use wider tape widths at faster speeds. For example, a 16-track 2" reel-to-reel tape machine recording at 30ips (inches per second) is a great option for multi-tracking, and half-inch 2-track at 30ips is excellent for mixdown. Note that the frequency response of tape is not linear, and will vary with tape formulation and speed so some experimentation is still needed but generally wider tape, at faster speeds is desirable when noise is a concern. This is why 4 or 8-track cassette multi-tracks are so noisy, the tape width is simply too narrow and the speed is too slow.
- The tape heads and transport on tape machines will slightly erase the higher frequencies of tapes upon each play. The problem is made worse if the machine has not been maintained in awhile and is due to be de-magnetized. This phenomenon is called self-erasure, and it can raise the noise floor over time as you eventually compensate for it with EQ. To combat this issue, you can either EQ to tape to make what's captured a little brighter (which will mellow out over time) or, make a copy of your multi track tape and mix using the copy, then switch back to the original recording when you are ready to do the final mix-down.
- Ensure that your tape machine is maintained regularly, particularly cleaning and demagnetization which will greatly impact audio performance.
- To minimize the noise floor, record as hot as possible when using analog tape, while bearing in mind the features or issues that come with that (tape compression, distortion etc.).
- Compress to tape to help record hot levels. EQ to tape (pre-emphasize the higher frequencies during recording and then use EQ to de-emphasize those same frequencies upon playback during the mix) to help further counter tape hiss.
- Consider using companding (compress to tape, re-expand upon playback) noise reduction technologies available for analog tape, which are designed to minimize tape hiss, bearing in mind that like any noise reduction technology, they are not a perfect solution, though, the artifacts of the compander may be the lesser evil compared to tape hiss. Please note that companding artifacts may become undesirable if you also record a hot signal to tape. Companding is less necessary for wider tape widths such as 2" 16 or 24-track or 1/2" 2-track.
- Use automation during mixing to mute any track that is not playing sound.
- Use EQ to reduce higher frequencies on tracks that do not need them (bass guitar, kick drum, etc.). The more tracks you can do this with, the more benefit you will hear from it.
Console noise part II
Remember that if you choose to record through your console, and then mix through your console later, you are adding extra console noise into your mix that can be avoided.
- Eliminate the analog mixing path. Mix using a digital mixing console or a digital audio workstation (DAW) in 32 or 64-bit float and maintain that throughout the production process.
- Passive mixers are an option, but by nature are very feature-limited relative to digital options.
Digital recording has removed the track-count limitations that we used to have with multitrack tape. In the days when 24 or 48 tracks were the maximum possible, the recording and mix engineers had to get creative with how they used those available tracks. Contrast that with today, where software-based DAWs have virtually unlimited track counts, you can easily have hundreds of channels of audio all generating varying levels of noise. Unless you have taken extreme measures to manage noise throughout the rest of the process, you will end up with a great deal of noise that has to be dealt with before you can craft a high quality mix.
- Avoid using analog tape. If you do, see my tips, above. When recording digitally, record in 32 or 64-bit floating point and maintain that precision throughout the entire recording and mixing process. If you record using an older 12 or 16-bit system, the dither (noise) applied to each track during recording will become obvious as you add more tracks.
- Reduce your track count. Avoid using many tracks when only one or two will do. If you can capture a drum kit with 6 microphones and 6 audio tracks, that is measurably better than 10 microphones and 10 tracks from a noise standpoint.
- Reduce your track count "dynamically". For example, use mix automation to mute tracks in a mix that are not playing any audio, or not contributing to the production in a meaningful way. If a track is "getting lost" in the rest of the mix, then consider muting it (is it adding anything to your mix if it can't be heard?).
- As with analog tape, consider using EQ to reduce frequencies that are not needed on each track. For example, lower the extreme highs on a bass guitar track or remove the lowest bass (which may include rumble captured in the room) from vocals.
Fact: Noise does not end when the production is finished.
I have covered several ways that you can reduce the noise in your productions. This is the noise we have control over. Unfortunately, consumer playback technology and listening environment noise are factors that we have no control over, but will continue to get between your listeners and your music. The clicks and pops of a dusty record, the noise of a car, a busy street, or a low-grade stereo system will still manage to erode the sound that you worked so hard to create. Bearing this in mind, always remember that noise is cumulative, and give your productions a fighting chance by making them as noiseless as possible.