Audio Tool can be calibrated for greater accuracy — an important feature given that there are so many types of Android phones and their different microphones, electronics and software will surely yield inconsistent results without calibration. All you need to calibrate Audio Tool is some sort of SPL meter.

Hook up a 3.5mm-to-dual-RCA cable between your phone and your hi-fi components and you can send test tones through your system: white noise, pink noise, impulse and various waveforms (sine, square, triangle and ramp). All the waves are frequency adjustable.

The RT60 function measures the amount of time it takes for a sound to decay to -60 dB of its original level. Just activate the RT60 and clap. It’s a useful measurement to gauge the effects of different acoustical treatments.

I can’t say Audio Tool is perfect. A couple of recent updates haven’t worked well on my Motorola Droid Pro phone; the buttons on the bottom of the display are cut off. That phone has a considerably smaller screen that most of the Droids I’ve seen, though. The app has a max SPL reading of somewhere around 85 to 95 dB depending on your phone — plenty for balancing home theater channels but not enough to measure high volumes. Also, Geoff Morrison, my partner in Tech^2, gets a 10 kHz “phantom tone” on the spectrum analyzer no matter where he goes.

With Audio Tool on your Droid, you always have a full-featured acoustical analysis tool right in your pocket for just a few bucks. It’s the best option I’ve ever seen for DIY audio testing.