This video was specifically created to answer questions posed by students in the graduate level noise control engineering course I teach at Penn State. I assign several hands-on projects that require students to obtain a Type 2 quality sound level (standalone sound level meter device or an accurate app for mobile phone).

This video shows that while the DecibelX Pro sound level meter app for iOS looks really nice and has some excellent features, it has accuracy problems when attempting to calibrate it with an external microphone (necessary to achieve Type 2 accuracy).

Along with this video I made several other videos comparing other apps, and calibration:
Faber Acoustical SignalScope X (on iPhone and iPad) --    • Comparing the accuracy of two Type2 i...  
Calibrating the Faber Acoustics SignalScope X --    • Calibrating an external microphone (M...  
NIOSH Sound Level App (on iPhone and iPad) --    • Comparing the accuracy of two Type2 i...  
Calibrating the NIOSH Sound Level App --    • Calibrating an external microphone (M...