SPL Graph is an audio level chart recorder for the iPhone and iPod Touch. It works by averaging the SPL for one second, applying an optional weighting filter, and plotting the sound level.

Check out our new video demo of SPL Graph. SPL Graph can record up to 24 hours of sound level data, with single second resolution. The graph starts with a one-minute window, and as a minute is recorded, the graph re-scales automatically and adds another minute to show the data collected so far. 

Note: When running from within AudioTools, you can upload the data and recorded audio files to your PC or Mac. The file format is .CAF, which is a compressed Apple format. You can convert it to a Windows-compatible file using a tool like AVS Audio Converter.

Graphics You can scroll and scale the graph vertically, in dB, by using standard swipe and pinch gestures. You can also scroll and expand and contract the time axis using gestures. Zoom out to a full 24 hours, or zoom in to a single minute, showing second resolution. Double-tap the screen to zoom out to show the entire graph on the screen. The time scale grid changes dynamically, highlighting minutes, ten-minute, and hour lines as as it runs. As the graph runs, the overall LEQ (average SPL) for the entire time period is computed and displayed on the screen. Swiping across the graph brings up a cursor that displays the exact dB level and time for any point on the graph.

Audio Recording

SPL Graph can record up to 24 hours of sound level data, with single second resolution. The graph starts with a one-minute window, and as a minute is recorded, the graph re-scales automatically and adds another minute to show the data collected so far. Tap the green play button to play back the recorded audio, and use the cursor to scrub the audio location on the graph. Use this feature to listen to events that you can see on the graph.

The audio is recorded 16-bit, 48k, mono, compressed with Apples 4-to-1 IMA4 compression algorithm. As such, one minute of audio consumes 1.44MB, and one hour consumes 86MB. A full 24 hour SPL Graph would use 2GB of space on your iPhone or iPod Touch. To free up space, you can always delete the graph and audio files from the Save / Recall page.

File Saving If you exit the app, or are interrupted with a phone call, the graph data will not be lost. SPL Graph will automatically save the graph, and reload it when you next open the program. You can also save a graph in one of ten files on the iPhone, so that you can recall the graph later.

SPL Graph supports saving up to 10 graphs directly on your iPhone or Touch. You can recall these graphs and bring them up on the screen, and listen to the sounds that were made while the graph was recorded. You can also store an image of the screen to your photo roll. Filters

The filters are all ANSI type 1 or better, and include A-weighting, C-weighting, and all octaves band filters from 32 to 16kHz. Like all Studio Six Digital audio apps, SPL Graph supports calibration. The app ships calibrated for a typical iPhone 3G. If you have access to a calibrated SPL meter you can calibrate your iPhone.

NOTE: This app was renamed from "LEQ Graph".

CALIBRATION

SPL Graph comes pre-calibrated for the typical iPhone built-in and headset mic, but you can adjust the cal if you have a professional, calibrated meter to compare it to.

To adjust the calibration, follow these steps:

* Set you reference meter to the same settings as SPL Meter (choose A and Slow, for example, on both meters) 

* Play pink noise or white noise through your system to get a reading on your reference meter in the range of 70-85dB

* Go to the settings page on SPL Meter (flip the screen over)

* Select the correct mic setting (normally Internal)

* Adjust the Trim field using the + and - buttons until the dB field matches the reading on your reference meter.

iPod Touch Compatibility