I haven’t tried every audio-oriented app for Android phones, but I’ve tried a bunch. Not surprisingly, the one I like best by far costs $6.99, which for an Android app is a truly Rolls Royce price. Yet it’s also the most insane deal of all time for DIY audio measurement software. Every audio professional I’ve demoed Audio Tool for has been downright shocked by what this app can do.

While Audio Tool does all sorts of cool stuff, the core function you’ll use most is the audio spectrum analyzer. The spectrum analyzer tells you which frequencies are present and at what level; you can use it to figure out what frequencies your speakers or your room are emphasizing or cutting. Audio Tool has three spectrum analyzer options: 1/3rd octave bars, 1/6th octave bars and a full-resolution line display. (I use the 1/6th octave setting most often.) I haven’t seen a free spectrum analyzer app that delivers such high resolution.

The measurements can be stored and recalled—a great feature for comparing the effects of different subwoofer positions.

A multicolored spectrograph shows the analyzer’s response over time; I haven’t figured out a use for it but it does look cool.

The sound pressure level meter feature gives you the same functionality as the famous RadioShack SPL meter. Basically it tells you the overall sound level. It’s useful for all sorts of things, but especially for balancing the various channels of a surround-sound system.

Like the RadioShack meter, Audio Tool has A- and C-weighting. Unlike the RadioShack meter (or any other inexpensive SPL meter I’ve seen), it has a flat setting with no weighting, which is a big help when you’re setting subwoofer level. It has a chart recorder function, too, which records SPL levels over time. And it has a live waveform display.