BandPass - Real-Time Audio Frequency Filter & Spectrogram

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+).

Quick Presets

Jump to common frequency ranges instantly: Voice (85Hz-3kHz), Rumble (20-250Hz), Whine (2-8kHz). Create and save unlimited custom presets for your specific diagnostic needs.

Recording & Playback

Record raw audio for later analysis. Play back recordings and adjust filters in real-time—perfect for comparing "before and after" or sharing diagnostic findings with others.

Adjustable Gain Control

Amplify quiet sounds up to 20x to hear subtle noises clearly. Essential for detecting faint bearing noise, electrical whines, or distant mechanical sounds.

100% Free & Private

No subscriptions, no ads during analysis, no cloud uploads. Your audio stays on your device. Professional diagnostic tools shouldn't require monthly payments.

🔧 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: Use presets for quick selection or fine-tune manually. 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: Free forever. Professional diagnostic tools shouldn't expire.
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.