Stop! What’s That Sound: Troubleshooting Audio Issues
Sound recording is a garbage in, garbage out process. That is, the sound quality of your final product can only be as good as the quality of the sound recordings that go into the project from the start. Too often, the words “get it in post” are uttered for things that can’t be fixed in post-production, or things that would best be corrected from the start.
We live in a world full of noises. Cars, HVAC systems, neighborhood dogs, lawn mowers and roosters often plague the recordists desire for clean sound. In addition to these audible sounds, a number of electrical, telecommunications and utilitary devices can cause electromagnetic interference that affect the consistency and quality of recorded sound.
There are, of course, a number of quick-fix solutions on the market to help improve audio issues. Many of them have extremely varying levels of efficacy. Most of them end up removing sounds that are desirable along with sounds that are unwanted. With that in mind, this article focuses on troubleshooting audio issues and preventing audio issues, and some tips in production or post production to prevent them.
When All Recordings Sound Bad
If recordings from other studios, especially music or voice from professional studios sound bad on your system, the most likely culprit is your monitors. As we discussed in An Intro To Studio Monitors, a good set of monitors will have a wide, flat frequency response, and represent your audio with clarity and precision. Consumer speakers and headphones are often weighted to produce what the manufacturer determines as a more pleasing sound to the listener. This weighting can adversely affect your listening perspective when mixing, and can even make a professional mix sound off.
Additional considerations may include your room’s acoustics or a need to properly EQ your monitors. However, 90 percent of the time, a decent set of near field monitors will fix most monitoring issues.
Dropouts during recording or playback
Audio dropouts and glitches like these are typically caused by a low latency buffer setting for recording or playback. Increasing the buffer in your recording software to 512 or higher will reduce dropouts and glitches at a cost of latency, or a delay between the time you speak and you hear the audio in your headphones or monitors.
Buffer – In computer terms, your input output (I/O) buffer determines the the size of the data chunks that are read from and written to your hard drive when recording and playing back audio. A low buffer setting demands more computing cycles from your CPU. Too low a buffer setting can cause unwanted clicking and stuttering in your audio during recording or playback. Too high causes more latency (delay) between the time you speak and the time your recorded audio is played back through your monitors. On most systems, when recording without effects, a setting of 256 creates an indistinguishable delay, but can also cause clicking if your CPU is too slow, or if you are using many tracks or effects at once. In these instances a setting of 512 or 1024 can be used at the cost of some latency.
If you hear distortion when monitoring mics or are getting clipping in your audio recordings, the most likely culprit is your gain staging. In its simplest form, the solution is to reduce your microphone’s gain (i.e. turn down your microphone). For more in-depth information on gain staging refer to Aural Fixation: Clipping and Gain Staging.
Hiss is most often caused by amplified self-noise somewhere in your signal flow. Every piece of equipment in your audio arsenal produces some hiss from self-noise. Microphones, pre-amps, effects racks and monitors are all likely culprits to check for hiss problems.
Often, proper gain staging will solve many hissing issues, along with some judicious use of gating and noise reduction. However, there are times when a piece of equipment, such as a microphone, can cause a distracting amount of hiss. Here are some options to try to eliminate hiss:
- If equipped, engage your pre-amp’s pad switch to attenuate (reduce) the hiss before the sound reaches your DAW. Alternatively, an inline XLR pad such as the Whirlwind IMP Pad or impedance matching adapter may be used.
- Use a microphone with lower self-noise. For microphone selection basics, refer to A Beginners Guide to Microphone for Voice.
- Use a lowpass filter set to 12 kHz to reduce high frequency hiss without adversely affecting vocal frequencies.
- Use an expander to increase the dynamics between the signal and self noise. An expander increases your audio signal’s dynamic range. Noise gates are a type of expander.
- Use noise reduction. Be careful to set reduction to not produce artifacting or reduce the quality of desirable audio.
- As a last resort, use a noise gate. Keep in mind that hiss may still be present when speaking.
Low Frequency Rumble
Low frequency rumble is by far the most common problem I tend to hear in podcasts. It is often overlooked due to monitors that don’t reproduce frequencies under 180 Hz well. Those of us who listen with monitors that produce lower frequencies, and especially those of us who listen through systems with a subwoofer are often confronted with a low frequency rumble that is distracting from the material.
Typically, low frequency rumbles are produced by HVAC systems, vehicular traffic, or computer noise that vibrates through the floor or desk into the microphone. Here are some common solutions:
- Reduce air conditioning noise or shut off air conditioning and heating systems while recording.
- Use a high pass filter set around 80 to 120 Hz.
- Use a microphone with a high pass or a limited low frequency response
- As a last resort, use noise reduction to eliminate rumble.
Radio Frequency Interference
Radio Frequency (RF) interference tends to come in the form of digital clicking and distortion produced by cellular phones or a distorted audio signal from a local AM radio station that can be heard over a recording. Other causes of RF interference are air conditioners, microwave ovens and any electronic device like a router or computer or bluetooth device that uses a wireless signal. Common solutions include:
- Ensure all cellular devices are off or not present in the studio when recording.
- Move routers, computers or other RF devices away from recording equipment
- Turn off wireless and bluetooth devices
- Use an inline RF filter to attenuate signals from AM radio stations and other RF interference
Hum is one of the most common occurrences in an audio signal. It is produced when electromagnetic interference from power wiring is picked up by your audio equipment. The interference comes in the form of a 60 Hz buzzing sound (50 Hz in Europe). The two most common causes are magnetic interference picked up by audio cables and a ground loops, which are caused by having two pieces of connected audio equipment attached to separate outlets with an unshared ground. Here are some methods of prevention:
- Use balanced audio cables shorter than 10 feet to connect equipment. For more information on cable management, refer to On the Care and Feeding of Cables: Don’t Cross the Streams.
- Do not use electrical ground adapters to remove a ground. In addition to noise, it presents a potential safety hazard.
- Connect equipment to same outlet that feeds power strips for your recording equipment.
- Isolate the outlet used for recording equipment. Use a separate outlet to power lights and other equipment.
- Use a ground lift or a direct box with ground lift to eliminate hum from ground loop.
- Check cables for broken shields and leads and replace or repair as necessary.
Now you are equipped with the most common types of interference in your audio signal and what to do about them. The more you know and understand about audio issues and how to prevent them, the better your recordings can be from the start, eliminating or reducing the need to use audio filters in post-production that can reduce the quality of your audio!
Need More Help With Your Podcast?
We've hopefully assisted you in working through any audio issues you've been having. But there's a lot more to running a podcast than the sound of the audio itself.
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