Digital Filter Designer
Start from a sample rate and desired cutoff or frequency band. The FIR option windows an ideal sinc with a Hamming window; the IIR option cascades one to three identical cookbook biquads. This is a coefficient design and inspection tool: it does not analyze or upload a sound file. Use the plotted, calculated response to check what the chosen design actually does before implementing it elsewhere.
Key features
- Four filter shapes with strict Nyquist and ordered-band validation
- Odd 15–255-tap Hamming-window FIR coefficients normalized at a pass-band reference
- One to three identical W3C Audio EQ Cookbook biquads with explicit numerator and denominator coefficients
- Independent 257-point magnitude and wrapped-phase evaluation and 96-sample impulse response
- Second-order IIR pole stability check and frequency probe values
- Download standalone response SVG, frequency CSV and complete design JSON
How to use
- Choose FIR or IIR and low-pass, high-pass, band-pass or band-stop shape.
- Enter a sample rate and a cutoff; for a band filter enter lower and upper edges inside the Nyquist limit.
- Choose an odd FIR tap count or an IIR order made by one to three identical biquad sections. Set Q for low- or high-pass IIR.
- Press Design and inspect the coefficient table, calculated frequency response and impulse response.
- Download the chart SVG, response CSV or coefficient-and-response JSON for review or implementation.
Use cases
- Sketch an audio low-pass before adding it to a signal-processing application
- Compare FIR transition width as tap count changes
- Study how IIR Q and repeated sections change resonance and roll-off
- Export a reproducible coefficient set with its measured numerical response
Frequently asked questions
Are the cutoff edges guaranteed to be exact?
No. A Hamming FIR has a finite transition band and pass/stop ripple. For band IIR, the geometric center and center divided by edge width define a nominal Q; bilinear warping means the entered edges are not exact 3 dB points. Inspect the calculated response.
What does IIR order mean here?
Orders 2, 4 and 6 are one, two and three copies of the same normalized biquad in cascade, not a maximally-flat Butterworth design of that total order. The exported second-order sections are the implementation form.
How is the FIR gain set?
The odd-length linear-phase FIR is normalized to unity at DC for low-pass and band-stop, at Nyquist for high-pass, and at the geometric band center for band-pass. Other frequencies can differ from unity.
Is the IIR filter stable?
The normalized second-order denominator is checked with strict Jury conditions. The tool reports only designs that pass; changing the coefficients after export can change stability.
Is phase unwrapped?
No. The chart and CSV show principal phase in radians from −π to π. Phase is omitted when the transfer magnitude is below 10⁻⁸ because it is not meaningful there.
Are audio files or settings uploaded?
No audio input is used. Design, graphing and exports run in the browser tab without a server processing request.
Privacy
Design settings and coefficients stay in this browser tab. The requested SVG, CSV and JSON files are generated locally.
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