dB Meter: Sound Level Meter

dB Meter is a functional tool designed for measuring and analyzing environmental noise and sound levels. By utilizing raw audio data directly from your device's hardware, this application provides measurements for personal, occupational, or environmental monitoring.
Technical Signal Processing
The application bypasses standard high-level audio APIs to process audio at a lower level:
Raw Audio Capture: Uses the Android AudioRecord API to Capture raw PCM audio at 48 kHz (with an automatic fallback to 44.1 kHz if 48 kHz is unsupported by the hardware). It does not use MediaRecorder compression.
DSP Pipeline: Processes signals through a structured digital signal processing pipeline: DC-offset removal → frequency weighting (via IIR biquad filters) → Root Mean Square (RMS) calculation → time averaging → logarithmic decibel (dB) conversion → calibration offset application.
Frequency Weighting: Supports real-time switching between A-weighting (for human hearing response), C-weighting (for low-frequency noise analysis), and Z-weighting (zero/flat frequency response).
Time Weighting: Offers Fast (125 ms integration) and Slow (1.0 s integration) response settings.
Measurement Metrics
Monitor sound exposure with a comprehensive set of metrics:
Instantaneous Levels: Current Level (L), Minimum (Lmin), Maximum (Lmax), and Peak Level (Lpeak).
Leq (Equivalent Continuous Sound Level): Measures the total energy of sound exposure over time.
Percentile Levels (L10, L50, L90): Statistical noise distribution metrics calculated dynamically using a histogram database.
Real-Time Interface
The main Dashboard displays active data clearly:
Digital Display: A prominent numerical read-out of current decibels alongside the selected weighting unit (dBA, dBC, or dBZ).
Visual Indicator Scale: A color-coded warning scale (green, yellow, red zones) based on customizable exposure limits.
Contextual Labeling: Textual environmental context matching the current noise level (e.g., quiet, office, concert).
Live Graphing: A Rolling real-time chart mapping decibel variations over a sliding time window.
Session Controls: Dedicated buttons to start, pause, reset, or save the current recording session.
Calibration Settings
To account for individual hardware variances, the app provides adjustable calibration tools:
Manual Offset: Adjust the decibel readout manually using a slider.
Reference Calibration: Enter a known reference decibel level from an external calibrator to let the system calculate the required offset automatically.
Reset: Easily Restore the factory default offset values.
History & Session Management
Keep a structured record of all captured sessions:
History List: Review saved logs showing date, duration, Leq, Lmax, and the weighting modes used.
Search & Sort: Locate specific logs using note-based text search, or sort the history list by date or recorded noise levels.
Detail Views: Access full post-session charts, comprehensive metrics tables (including Lmin, Lmax, Lpeak, and L10/L50/L90 percentiles), and add custom text notes.
Data Export: Export detailed session data into a CSV format using the system share sheet.
Precision Control: Toggle the display between whole integers or tenths of a decibel.
Warning Thresholds: Set custom decibel limits that trigger visual safety alerts.
Background Monitoring: Run measurements in the background via a persistent Android foreground service, complete with a status notification.
Visual Themes: Choose between Light, Dark, or System-default themes.
Error Handling and Signal Integrity
Clipping Detection: Monitors input signals for digital clipping and displays a visual warning if the microphone's physical limit is reached.
Sensor Warmup: Discards initial audio buffer cycles during initialization to prevent artificial startup spikes.
Interruption Handling: Safely manages active audio transitions, including occupied microphone resources, device input changes, background state transitions, and stream-reading errors.