Anti-Aliasing Filter Order Calculator
Compute the required analog anti-aliasing filter order to suppress aliasing below a target SNR for a given sample rate and signal bandwidth.
How to Use
- Enter sample rate, signal bandwidth (passband), and required aliasing rejection.
- Tool computes required Butterworth/Chebyshev filter order for fs/2 stopband attenuation.
Show Work
Formulas
History of Anti-Alias Filtering
Claude Shannon and Harry Nyquist formalized the sampling theorem in the 1920s-40s: any signal above fs/2 aliases into the baseband unless filtered. Early digital audio and telemetry systems relied on steep 7th-10th order analog filters before ADC. Modern sigma-delta converters (pioneered in the 1970s at Bell Labs) use heavy oversampling plus digital decimation to shift most alias rejection into the digital domain - reducing analog filter order to 1st or 2nd even for 24-bit audio performance.
About This Calculator
Enter sample rate, passband frequency, and required alias rejection in dB (typical = ADC ENOB × 6 dB/bit). The tool computes required filter orders for Butterworth (maximally flat passband) and Chebyshev (sharper transition, ripple).
For oversampling ADCs (sigma-delta, SAR with 4-8× oversampling), reduce analog filter order by 2-3 — the ADC\'s digital decimator handles the rest. Everything runs client-side.
About the Anti-Aliasing Filter Order Calculator
Need a hand with electronics and circuit design? The Anti-Aliasing Filter Order Calculator does the work for you — free, and right here in your browser. Compute the required analog anti-aliasing filter order to suppress aliasing below a target SNR for a given sample rate and signal bandwidth.
How it works
Type your numbers into the boxes. The answer shows up right away — you do not have to press a button. If you change a number, the answer changes too. So you can try different numbers and watch what happens, or check an answer you worked out yourself. Just make sure each box has the right kind of number in it.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Why anti-alias?
Signals above fs/2 fold back into the usable passband as aliases. Anti-alias filter attenuates them before the ADC. Target rejection: 10·log₂(2^ENOB) dB for the ADC\'s effective bits (e.g., 12-bit needs ~72 dB).
Guard band?
Ratio (fs/2)/f_pass defines the filter transition region. Wider guard band = easier filter, fewer poles. Oversampling (fs > 2·f_signal) trades ADC sample-rate for simpler analog filter.
Digital half?
Modern ADCs with integrated digital decimation filters do most of the alias rejection digitally, leaving the analog filter only to reject out-of-band signals beyond the decimation filter\'s stopband. Reduces analog filter order dramatically.
How do I use the Anti-Aliasing Filter Order Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Audio 44.1 kHz ADC
20 kHz passband, 22.05 kHz stop, 96 dB SNR: 5-6 order Chebyshev.
Oversampling ADC
1 MSPS ADC for 10 kHz signal: 50× guard band → 2nd-order Butterworth works.
Scope Front-End
1 GS/s, 500 MHz BW: 2-3 order Gaussian-response low-pass for smooth step response.
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