DecibelPeak

A fancy sound level monitor for iOS

Real-time decibel readings, frequency analysis, and several ways to look at the sound around you.

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About

DecibelPeak measures sound levels with your iPhone's microphone and shows them in real time. It reads the current level on a circular gauge, tracks the loudest moment of the session, and offers several visualizations of the live audio. It's meant to be useful and good-looking rather than a calibrated measurement instrument.

Demo video

Click the image to download and watch the demo (~30 MB, 60 fps).

Features

• Real-time level monitoring on a circular gauge spanning 20–130 dB over a 270° arc.
• Color-coded levels: blue (below 40 dB), green (40–60), yellow (60–80), orange (80–100), red (100 and above).
• Calibration: an adjustable offset of ±20 dB in 0.5 dB steps, with a snap-to-zero point. The setting is saved between launches.
• Session peak tracking: the app remembers the loudest moment of the session.
• Session average: an equivalent-level badge summarizing the session in a single number.
• Auto-start: monitoring begins on its own once microphone access is granted.
• Portrait and landscape layouts.
• Six languages: English, French, German, Spanish, Japanese, and Brazilian Portuguese.

Visualizations

The visualization area holds seven views. It cycles through them on its own while monitoring, and you can swipe or tap to move through them yourself.

1. Waveform — oscilloscope-style view of the audio signal.
2. Spectrum — amplitude spectrum of the current sound.
3. FFT Bars — frequency content as vertical bars across the audible range.
4. FFT Circle — the same frequency content arranged in a circle.
5. Waterfall — a spectrogram showing how frequencies change over time.
6. dB Curve — recent decibel levels over time.
7. dB Peak — a 60-second window centered on the session's loudest moment, with a dashed marker at the exact second it happened. Scroll horizontally to move through the window.

Screenshots

Technical details

Audio processing

• Sample rate: 44.1 kHz
• Buffer size: 1024 samples
• FFT via Apple's Accelerate framework (vDSP), with a Hann window
• Level computed from RMS, then converted to decibels with smoothing and an optional calibration offset
• Session average computed as an equivalent continuous level over the session

Rendering

Updates are driven by CADisplayLink and synced to the display refresh. The level and waveform redraw at the screen's refresh rate; the dB history is collected at 10 FPS to keep scrolling steady, and the waterfall updates at 15 FPS.

Architecture

• SwiftUI for the interface
• AVFoundation for audio capture
• Accelerate for the FFT
• An ObservableObject audio manager driving the views

Getting started

From the App Store

The easiest way to get DecibelPeak is from the App Store:

Download on the App Store

Requirements:

• iOS 17.0 or later
• Microphone access

Build from source

Requirements:

• iOS 17.0 or later
• Xcode 16.4 or later
• Swift 5.0
• An Apple Developer account for running on a device

Steps:

1. Clone the repository:

   git clone https://github.com/AndreFrelicot/DecibelPeak.git
   cd DecibelPeak

2. Open the project:

   open DecibelPeak.xcodeproj

3. Select your development team in the project settings.
4. Build and run on a device or the simulator.

On first launch the app asks for microphone access and starts monitoring once it's granted.

Usage

1. Grant microphone access; monitoring starts automatically.
2. Read the current level on the circular gauge.
3. Swipe or tap the visualization area to move between views.
4. Watch the Quiet / Moderate / Loud indicator at the bottom.
5. Use the calibration control to offset readings if needed.
6. Tap stop to pause.

Sound level reference

Range	Color	Description	Examples
Below 40 dB	Blue	Very quiet	Quiet room, soft breathing
40–60 dB	Green	Quiet	Library, normal conversation
60–80 dB	Yellow	Moderate	Busy traffic, vacuum cleaner
80–100 dB	Orange	Loud	Lawn mower, motorcycle
100 dB and above	Red	Dangerous	Concert, chainsaw, thunder

Prolonged exposure to sounds above 85 dB can damage hearing.

Project structure

DecibelPeak/
├── DecibelPeak/
│   ├── DecibelPeakApp.swift          # App entry point
│   ├── ContentView.swift             # Main UI with responsive layouts
│   ├── AudioManager.swift            # Audio capture and processing
│   ├── FFTAnalyzer.swift             # Frequency analysis
│   ├── CircularGaugeView.swift       # Circular gauge
│   ├── WaveformCarouselView.swift    # Visualization carousel
│   ├── WaveformView.swift            # Waveform display
│   ├── FFTVisualizationView.swift    # FFT-based visualizations
│   ├── Localizable.xcstrings         # Localized strings
│   └── Assets.xcassets/              # Icons and colors
├── DecibelPeakTests/                 # Unit tests
└── DecibelPeakUITests/               # UI tests

Localization

Strings live in Localizable.xcstrings. To add a language, open that file in Xcode, add the language, and translate the entries.

Contributing

Contributions are welcome. Useful ones include bug reports, feature ideas, new translations, documentation fixes, and pull requests.

1. Fork the repository.
2. Create a branch for your change.
3. Commit your work.
4. Open a pull request.

Author

André Frélicot

• GitHub: @AndreFrelicot
• Bundle ID: dev.andrefrelicot.decibelpeak

License

Released under the MIT License. See LICENSE for details.