TUAW's Daily iPad App: Decibel Meter Pro

Have you ever wondered just how loud a noise is? During a recent review of the SoundJaw iPad accessory, I needed to see if it really increased the volume of the iPad's speaker. What did I use to measure the sound level for the review? The iPhone version of Decibel Meter Pro (US$0.99, universal), a fun -- and useful -- app to measure the max, peak, and average dB (decibel) levels associated with a sound source.

To use the app properly, you must point the iPad's microphone (it's at the very top between the power button and headphone jack) directly towards a sound source such as a speaker. The app shows four meters, all of which rotate so that they're always vertical. There's one that displays peak sound pressure level as a number, one for max, and one that displays an average. There's also a large combo needle-type gauge that displays both peak and average dB levels.

Decibel Meter Pro provides four separate frequency weightings -- A, B, C, and Z (unweighted). According to the built-in users guide, "these weighting filters emphasize or suppress certain aspects of a frequency spectrum compared to others." The A-weighting is used most commonly since it measures sound pressure level with more sensitivity at the higher frequencies, just like the human ear.

During my tests with the iPhone version of the app, I found myself confused about certain aspects of sound pressure measurement, so I decided to check with the folks at Salt Lake City-based Performance Audio who make Decibel Meter Pro. I'm always used to waiting for a few days for answers, so I was shocked and pleased when I received an answer in just minutes. The support for Decibel Meter Pro is some of the best I've ever seen for any app.

Thanks to the "install once, install everywhere" setup for universal apps, I am able to enjoy Decibel Meter Pro on both my iPad 2 and iPhone. I find myself using the app a lot. I have a little bit of tinnitus in my left ear, so I find myself concerned about loud noises. I've measured the crowd noise at a Major League Baseball game (86 dB), at my desk (52 dB), and in a favorite restaurant during a busy time (72 dB).

There are a couple of little things to be aware of. First, tapping on the screen or rubbing against the iPad case will bump up the Max dB reading, but you can lightly tap the Max dB meter to reset it and get a more realistic reading. The other oddity is that when you first launch the app, the Max and Peak readings are huge numbers. Keep watching the Peak reading for about 30 seconds, and you'll see that it resolves into a reasonable number. You'll need to tap on the Max dB meter to reset it from the huge number you'll see. Finally, the app is advertised as having a decibel reference chart (it's shown in the description), but it's not actually in the app.

At US$0.99, Decibel Meter Pro is a bargain. It's a great tool for anyone who is concerned about noise levels or who needs a tool for measuring just how loud the neighbor's barking dog is.