Using Audio Files as Input Source

This document describes how to use audio wave files as the data source for audio processing functions.

Audio Files

AudioTools modules normally take their input from a live input source, such as the built-in microphone or one of the external options, such as iTestMiciPrecisionMic, or iAudioInterface2. Starting with AudioTools 9.4, you can now use a wave file for input, for some modules.  Functions that support this feature currently include RTA, FFT, Smaart Spectrum, SPL Pro, and SPL Graph.

Currently, only wave files using PCM format in either mono or stereo may be used for this feature.

Preparing an Audio File

The wave files must be stored in the SPL Graph public folder. All audio wave files that have been stored from the SPL Graph module will be automatically available.

If you want to use your own wave file, just copy it into the SPL Graph public folder. There are different methods to do this, depending on your file storage choice. Make sure that the file is a PCM encoded 16-bit wave file, mono or stereo, and recorded at 48k if possible. 44.1k will also work, but some functions in AudioTools expect the 48k sample rate. The files must have the ".wav" extension.

Using Internal Storage

If you are not using Dropbox or iCloud, connect your iOS device to a browser, just as you would to download a file. Navigate to the SPL Graph public page, and use the Upload File button to transfer the file to the folder on the iOS device.


Drop the wave file into the iCloud folder:


Selecting a File

Files are selected from the Input Sources page, which is accessed on the Setup page for the individual function, or from the Input button on the SPL Pro main page. This image shows the Input Sources button on the FFT setup page:

Screen Shot 2017-04-05 at 8.12.35 PM

Tap the Select Input File button to bring up a list of available files. 

Screen Shot 2017-04-05 at 8.12.44 PM

Any wave files that were saved from SPL Graph, and any wave files that you have manually placed into the SPL Graph public folder will also be shown in the list.

Tap the row that shows the file that you wish to use, to highlight it. It will show up in yellow. Then tap the Select File button to open the file and make it available to the analysis function, such as FFT or SPL Pro.

Screen Shot 2017-04-05 at 8.18.17 PM

Once you have selected and activated an input file, all modules that support external file processing will use that file, until you cancel the file processing and go back to live audio.

Audio File Navigation

On the main audio analysis module screen, after you have loaded a wave file you will see a moving slider. This represents the relative position in the audio file that is currently being processed. The file will be processed from the beginning to the end, and then the position will loop back to the beginning and processing will continue. For SPL Graph, processing will begin when you tap the Play/Pause button, as you would to start live audio analysis.

You can use the slider to change the current position in the file.

Going Back to Live Audio

To return to normal real-time audio processing, go back to the Input Sources page on any of the supported modules, and tap the Clear button in the toolbar. The functions will return to live audio  processing.

Re-selecting the Previous File

From any of the supported module's Input Sources page, tap the Reselect button in the toolbar. If a file was previously loaded, it will be re-loaded.


For external audio files, no attempt is made to calibrate the external audio to absolute dB SPL. You can, however, change the calibration that is applied to file. To do this, open the Settings->Microphone Setup page, and change the Trim value. For example, if it appears that the audio is +20 dB too high, enter a trim value 20 dB less than what is currently set.

You may wish to create a new calibration entry so that you do not alter the microphone live audio calibration. To do this, just tap the "+" on the top of the screen, and make your changes to that entry.

Also, you will probably want to disable microphone compensation, to prevent the current mic frequency compensation from being applied. This can be done globally, on the Settings->General->Global Audio settings page.