top of page
  • Writer's pictureMatthew Losey

Identifying and Diagnosing the Many Flavors of Audio Noise Problems in Church | How-to #14

Updated: May 2, 2023

This blog post will be a little different. I will be listing several different noise problems and work to help you diagnose them. Audio noise can plague the world of live and broadcast audio. It is caused by a variety of factors, from electrical interference to equipment malfunction, and can take many different forms. Analog noise, such as hiss and hum, has long been a common problem in audio systems since the beginning of electric audio reproduction. With the rise of digital audio technology, new forms of noise have emerged, such as quantization noise and aliasing, which can be slightly more nuanced. Quickly identifying different types of audio noise and their causes is essential for audio engineers and technicians who strive to deliver high-quality sound for their church.


Noise Flavors

Hum - A low-frequency noise caused by the presence of AC power or ground loops in the audio signal chain. It literally hums, and is constant. It typically expresses itself in the low-mid and low-frequency areas of the audio spectrum. A temporary fix would be to remove the ground, but a much better solution would be to hire an electrician to diagnose it and fix it.

Hiss - A high-frequency noise caused by electronic components in the audio signal chain, such as preamps or amplifiers. This is typically more of a white noise style sound that is most obvious above the 5000 hz frequency range. Sometimes you might be able to just reduce the highs in the eq or do a low pass filter. With vocals, piano, and other instruments with a lot of high-frequency information, this won’t be sufficient. Your electrical power systems may be interfering with LED/fluorescent lighting. It also could be because the source audio signal is too low, and you have to make up the gain by turning up the preamp. Fix that by ensuring properly isolated power or by hiring that electrician.

Distortion - A form of audio alteration that occurs when the signal level exceeds the capacity of the audio system. It can be heard as a harsh, crunchy, or gritty sound. This is usually simply because the signal is too loud and you are clipping the input channel on pre-amp—turn it down. If you are experiencing distortion and are well below the clipping threshold, you may have a microphone with a particularly low battery which causes this often in both older analog wireless and newer digital systems. If you still have distortion, you may have a damaged DI box, a broken microphone, or an issue of a cable developing a dry solder socket problem that needs to be repaired. The last possibility could be that your instrument output volume is too high, turn it down to 80% of max and re-evaluate. Pianos, keyboards, computers, and other instruments with an output volume (things without a microphone) all have the ability to distort in this way.

Feedback - A loud, high-pitched noise that occurs when the sound from a speaker is picked up by a microphone and then amplified again. I spoke to this issue specifically in another post here.

Popping and Clicking - These sounds are caused by sudden changes in the audio signal, such as when a microphone is turned on or off, or when cables are plugged or unplugged. Find the crap cable or input, re-solder, or replace it and move on with your life! Don’t swap everything at once, do it methodically, one input at a time until you find the singular source.

Dropouts - a sudden loss of audio caused by interference or connection issues. There are various causes, and I’ll list them below.

  • Wireless interference: Dropouts can occur when the wireless signal is blocked, interrupted, or interfered with by other electronic devices, walls, or physical obstructions. This is typically paired with a strange woosh sound in older analog wireless systems. With newer digital systems, it just drops out entirely and usually cleanly and goes up and down fairly regularly. Change the location of the antennae or remap all of your wireless radio frequencies.

  • Cable issues: Loose or damaged cables can cause dropouts in the audio signal. This is especially true for long cable runs where the signal may weaken over the distance. You could also tell your guitar player to swap out his instrument cable.

  • Power issues: Power surges, brownouts, and other power-related issues can cause dropouts in live and broadcast audio. You may experience only some pieces of equipment dropping out. This is because some electrical equipment has higher tolerances for electrical voltage variation. That is why I always recommend at the very least having a voltmeter plugged into the same system that you can reference for a quick disqualification of power issues. They can be purchased for very little on your favorite online store and it’s worth it.

  • Clocking issues: The first type of dropout is called jitter. Jitter is a type of digital timing error that can cause noise in the audio signal. It can result from imprecise clocking/timing of digital audio staying in perfect time with each other. To avoid clocking issues and resulting audio distortion, it is important to ensure that all digital audio equipment in a system is synchronized to the same clock source. With complicated systems, use a dedicated clock generator or the best practice is just to use your FOH board as the clock source since it likely has built-in clock synchronization capabilities.

Quantization Noise: Quantization noise is a type of distortion that can occur when converting analog signals to digital signals. This type of noise is created when the analog signal is sampled and rounded to the nearest digital value. The difference between the original analog signal and the rounded digital value is known as quantization error, which can result in audible white noise or distortion in the digital signal. The higher the bit depth, the smaller the quantization error and the lower the level of quantization noise. To minimize this noise, use high-quality analog-to-digital converters (ADCs) with high bit depths and low distortion. To translate, don’t use cheap garbage soundboards or audio interfaces.

Aliasing Noise: Aliasing occurs when a signal is sampled at too low a frequency, causing high-frequency components to be misinterpreted as lower-frequency components. This can result in unwanted noise in the audio and is similar to listening to music through a voicemail. A popular problem where this persists is with satellite radio. The “compressed” sound you hear is described as aliasing noise which is intentionally applied in the satellite’s case, but obviously not intentional in live audio.

Random Clicking That Echoes: This is the result of either sample rate conversion errors or a bad ethernet cable that is causing momentary blips in continuity. Sample rate conversion is the process of converting digital audio data from one sample rate to another. If the sample rate conversion is not done correctly, is not perfectly aligned with a faultless clock, it can result in artifacts like an echo of clicks or a periodic otherwise unexplained speeding up of audio.

Crosstalk: Crosstalk occurs when a signal from one channel of an audio system leaks into another channel. This can create unwanted noise or interference in the audio signal and it will drive you insane. It’s most obvious when there’s crosstalk with the click track across multiple inputs and bleeds into the FOH speakers. To fix this, you most likely either need analog audio board repair, a new DI box for the click input or to reinitialize your digital audioboard. If the initialization doesn’t fix it, go through the update process. You may need to call the manufacturer to bring the board to roll back to a previous update and then reapply updates while testing the crosstalk for each step.

Conclusion (TLDR):

  • Not all noise is created equal.

  • Don’t use cheap and unreliable cabling.

  • Don’t fix everything at once. Proceed methodically, one at a time.

  • For digital audio, use a single clock source that is powered on before everything else.

  • Use high quality AD (Analog to Digital) converters

Happy hunting and kill that noise!


Commentaires


bottom of page