SLUFS app for iPhone and iPad

SLUFS is an audio metering tool which provides somebody to measure the momentary (S) LUFS as laid out in the recommendation R128 issued by the EBU. The meter works on the mono audio stream generated by the built-in microphone. In the measurement, the audio data is treated as a stereo signal (this means a weighting of 2) to get an approximation for a stereo measurement. There are limitations in the frequency response of the devices mic port, thus the meter is expected only to show correct values if the measured audio is restricted in the same way.
(because of the missing frequencies (less energy) you will get to low LUFS-values). Maybe one can get rid of this if he uses an alternative audio line in device. On the support page you can download a (very brief) summary-pdf of my experiments.

But nevertheless, if you want to play around with the meter,
simply put your iphone/ipad in front of yourself, were you can readoff the scales properly. Calibrate the meter as following:

First, you need a calibration tone. You can get it from the app support page or from the EBU homepage.

Second, in the case of a -20bB LUFS testfile (which the file on the support page is), play it in the desired software. Adjust the audio volume of your monitors or shift the phone on the table around until you meet a peak (Dezibel) scale reading of -20dB.
(The LUFS scale should show about -20db LUFS)

Third - measure.

Please keep in mind, that calibration and measurement should be done in a preferably silent environment.

Alternatively you can also use a direct injection box (DI-Box) and the mic jack of the phone to get a line audio signal into the device. Also, but not tested yet, the audio-in supply of your favor maybe also work. (If you do so, i would be pleased to hear about your experiences.)

Notes:
Be aware of the frequency response limitations of the mic port!
To get valide results regarding the internal calculations (ingnoring the mic port limitations) make sure the device is running with
a sample rate of 48kHz. Out of the box it should! (Take a look at the display).

Feel free to contact me at [email protected]