How to Use RTA App
To use the Peek-A-Boo you will need to find an RTA app for your phone. RTA stands for Real Time Analyzer and it is an app that listens to the phone's microphone port and slices up the audio it hears into 31 bands just like the 31 bands of a standard equalizer that range from low frequencies to high frequencies so that you can instantly see any and all level differences amongst 31 slices of the sound spectrum. The RTA app that I recommend for the Peek-A-Boo is actually called RTA and is developed by Andrew Smith. This app is only available for iOS but fret not, there are lots of other RTA apps out there for Android as well.

Important RTA App Settings
Any good RTA app will have a settings section that allows you to load a microphone calibration file so that any deviations in a microphone used with the app can be accounted for. When you buy a microphone that is designed for laboratory testing the microphone comes with this calibration file which is just a text file containing performance data for your specific microphone and formatted so that it conforms to an industry standard.
When we use this app with the Peek-A-Boo we will not be using a microphone. Instead we will be physically plugging directly into the bike’s stereo system. But we still need to be concerned with the microphone calibration file because by default most RTA apps will load a calibration file for your phone's internal microphone, and that will totally throw off the accuracy of the app. So I have written a special calibration file that has a flat response for the microphone input. This file conforms to the industry format standards, so you should be able to use it with any RTA app. You can find the download link in the article below.