SPL Graph 8.8

SPL Graph is an advanced environmental noise analysis tool designed for real-time measurement and documentation of sound pressure levels (SPL). It functions as a frequency analyzer, chart recorder, and data logger, providing comprehensive insights into acoustic environments.

The application features the ability to plot sound levels over time, enabling users to visualize fluctuations in noise levels. Concurrently, it records audio during measurements, which can be played back to identify specific sound sources contributing to elevated SPL readings. An optional in-app purchase allows users to capture video recordings of relevant events for enhanced documentation.

Furthermore, SPL Graph offers optional modules for octave and 1/3 octave band analysis, which facilitate spectral analysis of recorded sounds. These spectral results can be visualized through a dynamic 3D plot, offering an intuitive understanding of frequency distribution over time.

The software computes various statistical parameters, including Ln SPL values and percentage-based levels such as L01, L10, L50, L90, L95, as well as maximum and minimum SPL values (LMax and LMin). Automatic notifications can be configured to alert users when sound levels surpass predetermined thresholds. The system also supports automated saving of measurement results at user-defined intervals, with options to email reports and continuously initiate new recordings for extended monitoring sessions.

SPL Graph operates by averaging SPL over adjustable periods ranging from 0.1 seconds to 60 minutes. It applies optional weighting filters—such as A-weighting or C-weighting—and records raw audio signals if enabled. When spectral analysis modules are active, the app captures octave and 1/3 octave band data for each interval, providing detailed frequency content over time.

For enhanced professional applications, users can connect external microphones like iTestMic, iPrecisionMic, or iAudioInterface2. These upgrades facilitate compliance with ANSI or ISO standards, including Type 1 or Type 2 calibration results. Calibration certificates can be obtained by sending equipment to authorized laboratories, ensuring measurement traceability and accuracy.

The app supports recording up to 24 hours of SPL data with one-second resolution. Its adaptive plotting system starts with a one-minute window that dynamically rescales and extends as new data is acquired, presenting an ongoing visual record of noise levels. The overall equivalent continuous SPL (LEQ) is displayed in real-time for the plotted interval.

Audio playback of recorded samples is available via the built-in interface, with cursor controls allowing precise navigation within the audio timeline—useful for correlating audible events with visual peaks on the graph. If spectral analysis modules are enabled, octave and third-octave band data are stored and viewable graphically on a 3D surface plot.

The user interface supports intuitive gestures for scrolling, zooming, and panning both vertically (dB scale) and horizontally (time scale). Double-tapping resets the view to show the entire measurement period—from one minute to 24 hours—at appropriate resolutions. The time grid updates dynamically to highlight relevant temporal divisions.

As measurements progress, SPL Graph continuously calculates LEQ values across the selected duration and displays these metrics prominently on-screen. Tap gestures reveal detailed SPL readings at specific timestamps along the graph's timeline.

Audio recording is optional but valuable for post-event analysis; recordings can be stored in compressed or uncompressed formats. When the app is interrupted—by an exit or phone call—measurement data is automatically saved and restored upon reopening. Multiple graphs can be saved locally within the app for future review or exported via iTunes Files Sharing or Dropbox integrations.

Graphs can be stored as image files on the device’s photo roll and exported alongside measurement data in tab-delimited formats compatible with spreadsheet applications through iCloud synchronization. All frequency filters are compliant with ANSI Type 1 standards or higher and include A-weighting, C-weighting, and octave filters spanning from 32 Hz to 16 kHz.