BandPass - Spectrum Analyzer

Isolate any frequency range in real-time and hear the result instantly.
Essential for chasing down a rattle, a whine, or a bearing on its way out —
before you start pulling parts.

🎚️ BANDPASS — Professional Real-Time Audio Filter

🎛️ REAL-TIME FILTERING
• Touch-drag to isolate any range from 20Hz to 20kHz
• Hear the filtered result live as you move — no render, no wait
• 8-stage Butterworth bandpass at 96dB/octave for hard isolation
• Click-free retuning — coefficients crossfade over ~6ms instead of popping
• Record the filtered signal or the raw source, your choice

📊 DUAL VISUALIZATION
• Waterfall spectrogram — watch frequency content scroll over time
• Spectrum analyzer bars — full-screen landscape FFT view
• 2048-point FFT with windowing to control spectral leakage
• Frequency guides at 20, 50, 100, 200, 500Hz, 1, 2, 5, 10, 15kHz
• Pinch to zoom the band you're working in

🔊 TWO INDEPENDENT GAINS
• Display gain — brighten faint detail in the visualization, in dB
• Output gain — boost what you actually hear, up to 10x
• Tune what you see and what you hear separately

🎯 WHO IS THIS FOR?
Mechanics diagnosing engine and transmission noise, HVAC techs tracking
rattles and vibration, musicians analyzing harmonics and overtones, audio
engineers working off a phone — and ghost hunters (we don't judge).

🔬 THE SCIENCE
Audio is captured at 44.1kHz and run through eight cascaded biquad stages —
four highpass, four lowpass — forming a Butterworth bandpass with a 96dB/octave
rolloff. Filter state persists across retuning, so dragging the band doesn't
reset the delay registers or click. Visualization runs a 2048-point FFT with
gamma correction on the color ramp, so the noise floor stays black and only
real signal gets color.

🔒 PRIVACY — NO INTERNET, AT ALL
BandPass does not request the internet permission. It cannot phone home,
cannot serve ads, and cannot upload your recordings, because it has no network
access to do it with. Everything runs on your device. Your audio never leaves it.

💾 FREE VS PRO
Free includes the full filter, both visualization modes, both gain controls
and the complete 20Hz-20kHz range — the core tool, uncrippled.

A one-time Pro purchase adds:
• Recording, with no time limit
• Playback with live filter adjustment — re-filter a recording as it plays
• WAV import — bring in audio from a better mic and analyze it here
• Custom presets — save and name the bands you come back to

No subscriptions. No ads. No account. Nothing expires.

⚠️ HEADPHONES REQUIRED
Live monitoring feeds your mic output back to your ears. Use headphones or
you'll get a feedback loop.

🆘 SUPPORT
Email: [email protected]
Website: https://prodirt-llc.github.io/bandpass/