Interactive DSP Parametric Filter Sandbox
Instant DSP Filter Presets
Click any preset card to instantly load parameters and audition live spectral filtering.
Understanding Audio Biquad Filters & Frequency Response
Biquad filters are second-order Infinite Impulse Response (IIR) digital filters implemented according to Robert Bristow-Johnson's Audio EQ Cookbook ↗ and the W3C BiquadFilterNode specification ↗:
- High-Pass Filter (HPF): Passes frequencies above cutoff while rolling off low rumblings below cutoff at -12 dB/octave. Essential for eliminating microphone handling rumble, HVAC noise, and subwoofer port over-excursion.
- Low-Pass Filter (LPF): Passes low frequencies while attenuating high treble hiss, ultrasonic interference, and digital DAC aliasing harmonics.
- Band-Pass Filter (BPF): Isolates a narrow musical frequency band determined by the center frequency and resonance Q factor.
- Notch Filter: Surgically removes a pinpoint frequency spike (such as 50Hz or 60Hz AC electrical power hum) with minimal side attenuation.
The Q Factor (Quality Factor / Resonance)
In parametric filtering, Q = f₀ / Bandwidth. A low Q (0.5 to 0.707 Butterworth) creates a broad, musically smooth slope. A high Q (5.0 to 15.0) focuses filter energy into an ultra-sharp surgical cut, perfect for notching out ground loop hums or acoustic feedback without affecting nearby musical harmonics.
Real-Time Spectral Verification
The live spectrum visualizer above displays the 4096-point FFT transfer function in real time. Compare the raw signal against the filtered output using the Filter Active / Bypass toggle to evaluate phase impact and attenuation depth.
Frequently Asked Questions on DSP Audio Filters
Comprehensive breakdown of filter types, Butterworth vs Chebyshev vs Bessel, FFT/DFT transforms, and DSP pros & cons.