Isolate Any Sound Frequency

BandPass transforms your phone into a professional audio frequency analyzer and filter. Isolate specific sounds from background noise—perfect for diagnosing vehicle problems, troubleshooting machinery, analyzing audio recordings, or exploring the hidden frequencies around you. See and hear what you've been missing.

🎛️ Professional-Grade DSP

BandPass uses cascaded 4-stage biquad filters (48dB/octave rolloff) for surgical precision in frequency isolation. The same digital signal processing technology used in professional audio equipment, now in your pocket.

✨ Key Features

Real-Time Frequency Filtering

Drag interactive handles on the live spectrogram to select exactly which frequencies you want to hear. Everything outside your selection is silenced—isolate engine whines, bearing noise, or any specific sound instantly.

Live Spectrogram Waterfall

See sound as it happens with a scrolling frequency visualization. Logarithmic scaling highlights the full audible range from deep rumbles (20Hz) to high-pitched whines (15kHz+).

Custom Presets (Pro)

Save the bands you keep coming back to and name them — "car idle", "bearing whine", whatever the job is. Load one and you're straight back where you were, no re-dragging.

Recording & Playback (Pro)

Record what you're hearing with no time limit, then play it back and adjust the filter live during playback—perfect for comparing "before and after" or sharing diagnostic findings with others. Import your own WAV files and run them through the filter too.

Two Independent Gains

Boost what you hear up to 10x with the output gain, and brighten faint detail in the visualization separately with the display gain. Essential for detecting faint bearing noise, electrical whines, or distant mechanical sounds.

Private by Design

BandPass doesn't request the internet permission at all. It cannot phone home, cannot serve ads, and cannot upload your recordings — there's no network access to do it with. The filter, both visualizations and the full 20Hz-20kHz range are free; Pro is a one-time unlock, never a subscription.

🔧 Built For

Automotive Diagnostics

Isolate engine knock, bearing whine, belt squeal, exhaust leaks, or electrical noise. Find the exact frequency of mysterious sounds to diagnose issues faster.

HVAC & Appliance Repair

Identify compressor noise, fan bearing problems, or vibration frequencies in refrigerators, AC units, and machinery. Filter out ambient noise to focus on the problem.

Audio Production

Analyze recordings for unwanted hum, electrical interference, or specific frequency problems. Perfect for field recording troubleshooting and acoustic analysis.

Home & Building

Track down mysterious humming, buzzing, or vibration sources. Isolate HVAC noise, plumbing sounds, or electrical interference frequencies.

Electronics & Ham Radio

Analyze RF interference, power supply noise, or audio circuit issues. Visualize and filter specific frequency bands for troubleshooting and testing.

Education & Exploration

Explore the frequency spectrum of everyday sounds. Perfect for teaching acoustics, physics, or music theory with real-world examples.

How It Works

Start Monitoring: Tap START to begin real-time audio analysis. The spectrogram immediately displays all frequencies from your microphone.
Adjust Frequency Range: Drag the green handles on the spectrogram to select your target frequency band. Everything outside is filtered out instantly.
Fine-Tune & Listen: Drag the handles to narrow in on the band you want. Increase gain to amplify quiet sounds. The filtered audio plays in real-time.
Record & Analyze: Tap the record button to capture raw audio. Play back recordings later and adjust filters to isolate different sounds from the same recording.

The ProDirt Difference

Like all ProDirt apps, BandPass follows our core principles:

No Subscriptions: The filter and both visualizations are free forever. Pro is a one-time unlock, not a rental.
Privacy First: Your audio stays on your device. No cloud uploads, no tracking, no permissions beyond microphone access.
Works Offline: No internet required. Use it anywhere, anytime—in the garage, under a vehicle, or in remote locations.
Built by Problem Solvers: Created by someone who actually diagnoses mechanical issues, not just another generic audio app.