In today’s digital audio world, there are many technical terms that may seem confusing at first glance. One of them is aliasing. It is a phenomenon that can seriously affect the quality of an audio recording or sound synthesis, especially if you are working with digital processing, plugins or software synthesis. Let’s figure out what it is, where aliasing comes from and how to avoid it.
What is aliasing?
Aliasing is a signal distortion that occurs when the sampling rate is insufficient during the conversion of analog audio to digital or during digital signal processing. Simply put, it is when high-frequency components of the sound are “masqueraded” as low-frequency ones, creating false frequencies that were not actually present in the original signal.
The word “alias” in English means “pseudonym”, “another name”. In the context of audio, this means that one frequency “pretends” to be another. This is comparable to the moiré effect in video: when the pattern is too small for the camera, strange, flickering shapes appear. The same thing happens with audio if certain rules of digital recording are not followed.
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Why does aliasing occur?
The main reason is the violation of the Nyquist-Shannon theorem. According to this theorem, in order to accurately digitize an analog signal, the sampling frequency must be twice as high as the highest frequency in the signal. For example, if you record a signal with frequencies up to 20 kHz (the upper limit of human hearing), the sampling frequency must be at least 40 kHz. That is why the standard frequency in audio recording is 44.1 kHz. If this rule is not followed, frequencies exceeding half the sampling frequency (the Nyquist threshold) begin to “reflect” downwards and turn into false, inharmonic sounds.
How does aliasing manifest itself to the ear?
Alliacing is not like noise or clicks. It is rather an unpleasant, distorted overtone that sounds unnatural and can seriously spoil the audio quality. In synthesizers and VST plugins, aliasing most often manifests itself as “ringing” artifacts, especially when playing high notes, using distortion or aggressive compression.
To the ear, aliasing can manifest itself as:
- ringing, “metallic” tint;
- hoarseness and harshness in the highs;
- “dirtiness” in the sound during complex processing.
Where is aliasing most common?
In digital synthesizers and wave generators. Some synthesis algorithms (e.g. hard sync, FM, wavetable) tend to generate high-frequency harmonics, which, if the sampling rate is insufficient, cause aliasing. When using distortion/overdrive effects. These effects add harmonics that easily exceed the Nyquist frequency. In resampling and lo-fi processing. When audio is “downsampled” to a lower bitrate or sampling frequency without appropriate filters. In bounce-in-place and offline rendering. Some plugins use oversampling in real time, but may give different results when rendered.
How to deal with aliasing?
There are several ways to avoid or minimize aliasing:
- Oversampling. This is one of the most effective methods. A plugin or synthesizer internally increases the sampling frequency several times, processes it, and then returns the signal to the original frequency using an anti-aliasing filter. Many modern plugins (e.g. FabFilter, Serum, Vital) have oversampling settings — from 2x to 16x and higher.
- Using analog filters. Analog or virtual-analog low-pass filters can “cut” high-frequency harmonics before they cause aliasing.
- Working with high sampling rates. If your project allows it, use 48, 88.2 or even 96 kHz. This reduces the likelihood of aliasing during processing.
- Choosing high-quality VSTs and effects. Some free or outdated plugins do not take aliasing into account. It is better to use proven tools that indicate the presence of oversampling or anti-aliasing algorithms.
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Alliacing as an artistic device?
Fun fact: Some musicians and producers deliberately use aliasing as an effect. For example, in the chiptune or lo-fi genres, the sound with artifacts is perceived as “vintage” and atmospheric. Alliacing becomes part of the sound – rough, mechanical, but authentic.
Alliasing is not just a technical term, but a real problem that can significantly affect the quality of the sound. Understanding how it occurs and how to deal with it helps musicians, sound designers and engineers get clean, professional sound. If you work in a digital environment, do not forget to check the sample rate and oversampling settings – especially in synthesizers and when using effects that add harmonics. And remember: even such “technical” things as aliasing can become part of the creative process – if you know how to use it wisely.
