Aliasing happens when a signal is sampled at a rate lower than twice its frequency. The sampled data cannot distinguish the original frequency from a lower "alias" frequency, causing distortion or incorrect readings.

What is the Nyquist frequency?

The Nyquist frequency is half the sample rate (f_s / 2). To capture a signal accurately, the signal frequency must be strictly below the Nyquist frequency. At or above it, aliasing occurs.

How is the alias frequency calculated?

The alias frequency is the absolute difference between the signal frequency and the nearest integer multiple of the sample rate: |f_signal - round(f_signal / f_s) * f_s|. This folds the out-of-band frequency back into the 0–Nyquist range.

How do I prevent aliasing?

Use a sample rate more than twice the highest signal frequency (the Nyquist criterion), or apply a low-pass anti-aliasing filter before sampling to remove frequency components above the Nyquist frequency.

Does this tool work for audio signals?

Yes. Enter the audio frequency (e.g., 20000 Hz for 20 kHz) and your audio sample rate (e.g., 44100 Hz for CD quality) to check for aliasing in audio systems.

Aliasing Checker

Enter a signal frequency and sample rate to check for aliasing using the Nyquist theorem, and see the alias frequency if aliasing occurs.

Signal Parameters

Signal Frequency (Hz)

Frequency of the input signal in hertz

Sample Rate (Hz)

ADC or system sample rate in hertz

Quick Examples

Enter a signal frequency and sample rate, then click Check for Aliasing.

Summary

Checks whether a signal frequency will alias given a sample rate. Uses the Nyquist theorem to determine if the signal is safely below the Nyquist limit, and calculates the exact alias frequency when aliasing does occur.

How it works

Enter the signal frequency (Hz) and sample rate (Hz) in the input fields.
The tool computes the Nyquist frequency as half the sample rate.
If the signal frequency exceeds the Nyquist frequency, aliasing occurs.
The alias frequency is calculated using: |f_signal - round(f_signal / f_s) * f_s|, folding the frequency back into the baseband.
Results show clearly whether the signal is safe or aliased, with the exact alias frequency.

Use cases

Verify an ADC sample rate is high enough before capturing a known signal.
Find the audible artifact frequency when audio is undersampled.
Design anti-aliasing filter cutoff points for a data acquisition system.
Teach or learn the Nyquist sampling theorem interactively.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu