Note: There is a page with similar content at Reducing noise. Probably it should be merged with this page.
This page is a work in progress, on the topic of how to reduce extraneous noise in your recording.
Noise reduction is the constant challenge for the recording engineer. This page is for discussion of ways to improve your recording by reducing noise. This topic somewhat overlaps the issues of Improving recording quality, so be sure to check that page for tips as well. And, since the advent of inexpensive recording hardware and software like Audacity, there has been a huge boom in home recording. Thus, there is an enormous wealth of information available on the Internet, as evidenced by Google searches like this: Home Recording You might start your investigation with http://www.homerecording.com/ .
- Use a directional microphone. Cheap PC mics, besides having rotten sound quality, are nearly omnidirectional (i.e. they pick up from almost all directions equally). Many professional mics (Shure SM57 and SM58 for example) are highly directional. If the business end is not pointing at the noise source, it won't pick up the noise. It may still pick up ambient noise, including any sound originating elsewhere in the room and bouncing off the walls. That will be reduced if you put the microphone right on top of the sound source. When recording vocals, the performer's lips should almost be touching the mic, and sing straight into it (not across the top). Ambient noise will be blocked by the singer's head.
- Use a noise-blocking stand and distance the mic from the computer. Often times the vibrations from a computer's fans and drives will vibrate the computer desk and the surrounding area. If the microphone and its stand are on the computer's desk, the microphone often will pick up the vibrations and produce a noise on the audio track (often referred to as a "warble" sound: a soft, repeating hum). To help prevent this, use a ceiling-supended microphone stand or a full-size floor stand that can have its height adjusted. If these (pricey) options are not available, an alternative is to support a desk stand using a sound-insulating lift, such as a flimsy cardboard shoe box or a number of newspapers. These things insulate the noise rather well, making it difficult for any vibration noises to flow through to the microphone. Most any lift made of non-rigid, flexible material will do.
- Direct connection. If recording instruments like keyboards and electric guitars, feed their signal directly into your sound card's line input, or to a sound board and then into your PC. Guitars will need preamps. If you're recording acoustic instruments, use directional microphones placed close to the instrument, or use a pickup with preamp and connect direct.
- Get the desired signal as loud as possible (without clipping) into the microphone. This allows you to reduce the gain, which will also reduce the low-level noise. The further a microphone is away from the source, the more you have to amplify the mic's input signal to get to a usable level. But, boosting the gain amplifies everything, including background sounds and even the internal electrical noise of the amplifier. Ideally, the microphone should be right on top of the source*, with the gain no higher than necessary to get peaks around -3dB. If you are doing multitrack recording, record each individual track as loud as possible. Set the final volume of each track during post-production mixdown.
Note: placing the microphone "right on top of the sound source" might not be ideal when recording certain sources (such as bowed instruments like violins and cellos). Instead of placing the mic right on top of your sound source without regard to factors other than noise, you should experiment with different kinds of microphone placement until you find one that provides the best sound. If the "optimal" placement is too noisy you can look for other ways to reduce the noise. In the end, nothing beats an ideal recording environment.
- Post-recording noise reduction. Noise can often be reduced during post-production, by use of various plugins. Typically, they are fed a sample of the noise alone and then subtract that noise from the rest of the recording. To facilitate this, be sure to record a second or two of "silence" before you start the actual performance. This gives you a clean sample of the noise. This works extremely well with low-level background sound like air conditioning.
- Don't forget the possibilities of non-technical noise reduction.
- Turn off your refrigerator and furnace / air conditioner during the recording session.
- Hang blankets on the walls, to dampen a live room. Or record in a room with wall-to-wall carpeting.
- Record in a basement, to help isolate your session from outside noise. You'll probably need to use the blanket-on-the-wall trick here, since concrete walls make good sound reflectors.
- Record late at night to reduce traffic noise leaking in from outside. (It's up to you to work this out with the neighbors.)
- Do a Google search on Quiet PC or Silent PC for all kinds of sites with tips and techniques for reducing the sound out of your PC.
- If using a laptop, don't use its built-in mic. Besides being cheap and omnidirectional, it will pick up a lot of the mechanical noise of the laptop itself.
- Directional microphones. (see above)
60/50 Hz hum
- A common problem. Make sure all your recording equipment is connected to the same ground. This is easiest to accomplish by plugging everything into the same power strip.
- If all else fails, get rid of the hum during post-production by using a de-noise plugin or an extremely narrow notch filter.
- Try to use incandescent light bulbs (including halogen lamps); avoid using fluorescent lamps near a signal path (cables and equipment), especially for low-power signal lines such as microphone cables. Fluorescent lamps often generate a significant amount of high-frequency RF noise, which may then be captured by the cable or the equipment. Lamps on the ceiling do not usually induce buzzes (because they are far away), but if used in a group of 4 or more, they may introduce buzzes into the power line, which may affect other equipment on the same power circuit. Power conditioners may be used to alleviate this problem.
Inside your equipment
- Digital hash