What The Hell Is Aliasing? How Do I Avoid It Even If I Can't Hear It?
Updated: Feb 9
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In this post you will learn the ins and outs of avoiding aliasing in your digital audio workstation (DAW) with this concise and comprehensive guide. Discover the causes, symptoms, and solutions to achieve pristine sound quality.
As DAWs evolve, it is becoming increasingly important to understand how to avoid aliasing. In my line of work, I encounter it all the time in the projects that come in for mixing and mastering.
But then again... a lot of people can't hear this phenomenon. Sometimes it's negatively impacting your listening experience and you don't know why, but other times, it's just not really audible.
Regardless, aliasing is artifacts and distortion, and we don't want them informing our dynamics controls, or creating additional distortion when run through our saturation and distortion plug-ins.
What the hell is aliasing?
Aliasing is a form of digital distortion that occurs when the samples recorded in a DAW exceed the Nyquist frequency, resulting in a loss of high-frequency information, thus a degradation of sound quality. The Nyquist frequency is the highest frequency that can be accurately represented in a digital signal, and it is equal to half the sample rate.
One of the most common symptoms is a high-pitched, "sizzling" or "hissing" sound in the upper frequencies of your audio. Another sign of aliasing is a "smearing" or "blurring" of high frequencies. This can mess up details and clarity in the top of the treble range.
Steps to Avoid Aliasing in Your DAW
Use a higher sample rate: One of the most effective ways to avoid aliasing is to use a high sample rate in your projects. This will increase the Nyquist frequency, which reduces the chances of aliasing appearing in your audio. If you typically use 44.1 kHz as your native sample rate, consider hiking that up to 48, or even 96. According to many engineers 96 is unnecessary, but aliasing is more common in 44.1. Top engineer Chris Lord Alge swears that 44.1 and 96 sound better than 48, despite 96 being half of 48, but you can decide for yourself.
Use high-quality A/D converters: Another way to reduce the risk of aliasing is to use high-quality analog-to-digital converters (A/D converters). These things will accurately capture the high-frequency information in your audio which reduces the risk of aliasing. It will not completely remove the risk however. The next tip is a more sure-fire way.
Use a low-pass filter: Another way to avoid aliasing is to use low-pass filters. These filters (which can be accessed in virtually any EQ plug-in) will help to remove any high-frequency information that exceeds the Nyquist frequency. Sometimes notch filters will be needed, depending on what you're dealing with.
Use proper signal routing: Good signal routing is a very important factor in avoiding aliasing in your DAW. Avoiding the use of direct boxes, effects loops, and other processing that can introduce high-frequency information into your audio recordings can reduce or remove the possibility that aliasing will show up in your recordings.
Use oversampling: Many plug-ins these days have oversampling built in. Other plug-ins allow you to turn it off and on, and some of these plug-ins, like the Fabfilter Pro-L 2 (which is my favorite limiter) will let you choose different amounts of oversampling. Oversampling can improve the resolution and signal-to-noise ratio in your audio. It also helps you to avoid phase distortion.
A note on oversampling
Many engineers claim that overdoing your oversampling may be negatively impacting the sound of your mixes. This can be true in extreme cases. The golden rule in audio production it to use your ears. If anything you may not need to be oversampling too heavily. The Fabfilter Pro-L 2 limiter that I mentioned above will let you oversample 2x, 4x, 8x, 16x, and 32x. When I engineer recordings for clients, I usually don't oversample over 4x with it, though I used to do 8x. Higher oversampling rates are more CPU intensive. Maybe another time we can get more into what oversampling actually does.
Aliasing in sample-based music
When grabbing samples off the internet to slow down and sample in your productions, you may be bringing whatever aliasing is present and shifting it down in the frequency spectrum to an even more audible range. Many people cannot hear aliasing due to normal wear and tear on their ear drums. But if you pitch it down, it will be easier to discern, and more people will notice it.
So many of the vaporwave releases I've mastered have had this problem. Even by well-known and skilled producers. It is often overlooked.
If you are going to use lossy files as samples, it is important to low-pass them as suggested above *before* you slow or pitch them down. This way you shave off the aliasing before it becomes even more prominent. Aliasing can be subtle as it exists at the very tippy top of the audible range in human hearing. But if you slow down your sample a great amount, the aliasing will be even easier to hear. This can result in songs with high pitch sizzling that is quite unpleasant to listen to. Some producers find it pleasing as it adds to the lo-fi nature of the production, but even as someone who joyfully produces, mixes, and masters noise music, I never like hearing aliasing.
If you are unable to hear aliasing, you will be able to see it on a spectrum analyzer. There will be some kind of spike at the top of the frequency spectrum.
What plug-ins can I use to see evidence of aliasing, even if I can't hear it?
The best way to know if aliasing is present in your audio if you can't hear it (and even if you can) is a high quality spectrum analyzer. Many EQs have them built in, like the TDR SlickEQ, Arturia EQ SITRAL-295 or my favorite, the Fabfilter Pro-Q 3.
As for stand-alone metering with spectrum analysis, I would recommend the Meldaproduction MMultiAnalyzer for the tweakability and features. Meldaproduction is one of my favorite developers.
You could also try the popular iZotope Insight 2 as it does spectrum analysis as well as 6 other useful metering styles. I use Insight 2 when I need to look into something very specific, or multiple things at once. For example, I often use it when I want to look at the stereo field and the LUFS measurements at the same time. This is very useful in my mixing and mastering projects because sometimes it is necessary to EQ the stereo field, and that will have at least a subtle effect on the overall loudness of the audio.
However, be careful. Using metering and not your ears is one of the most common mistakes mixers, mastering engineers, and producers make. It can not only lead you astray, but make you concerned about things that really don't matter in the end.