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A filter's "order" directly determines how steeply it attenuates frequencies past its cutoff — higher order means a sharper, more decisive cutoff. This calculator converts a filter order into its roll-off steepness, expressed both in dB per decade and dB per octave.
How it works
Enter the filter order (N), and the calculator applies Roll-off = 20N dB/decade, and the equivalent 20N·log₁₀(2) dB/octave.
- Enter filter order (N).
- Click Calculate to see your results.
Examples
A standard 2nd-order filter
A 2nd-order filter rolls off at 40 dB/decade (about 12 dB/octave) — twice as steep as a simple 1st-order filter's 20 dB/decade (6 dB/octave).
Who should use it
- Filter design coursework and reference.
- Comparing filter steepness requirements across different orders.
Industry applications
- Electronics and signal processing
- Audio engineering and RF filter design
Advantages
- Simple, direct conversion from filter order to both common roll-off units.
- Useful quick reference for filter design decisions.
Limitations
- Describes the asymptotic (far from cutoff) roll-off rate only — actual filter response near the cutoff frequency depends on the specific filter type (Butterworth, Chebyshev, etc.).
Common mistakes to avoid
- Assuming a higher-order filter has no downsides — steeper roll-off often comes with more design complexity, cost, and potential phase distortion near the cutoff.
- Mixing up dB/decade and dB/octave figures when comparing specs from different sources.
Best practices
- Choose the lowest filter order that meets your actual attenuation requirements — unnecessarily high order adds cost and complexity without benefit.
- When comparing filter specs from different sources, confirm whether they're quoting dB/decade or dB/octave before comparing numbers directly.
Tips
- If you need a specific roll-off numerically (e.g. "at least 60 dB down two decades past cutoff"), work backward from the required dB figure to find the minimum filter order needed.