By Armando Rodriguez
Ask any seasoned runner and they'll be quick to tell you that keeping a steady pace is almost as important as staying hydrated. Listening to music is one good way to keep a steady running rhythm, but it can be tricky to put together a playlist of songs that all have the same tempo. After all, the last thing you need is for some mellow song to pop up in the middle of your high-intensity workout. 
PaceDJ is an app for iOS and Android that helps you build better playlists for your exercise routines. PaceDJ takes the music on your device and analyzes each song's beats per minute (BPM) count. PaceDJ uses EchoNest to identify the the BPM for each of your songs, though you can always change the BPM of a song if you think it's inaccurate. To do this, you simply tap the screen to the beat of the song, and PaceDJ does the rest. By using each song's BPM, the app can create playlists that contain songs with similar tempos. You can adjust the types of songs that play by adjusting the BPM on the main screen, or by thumbing down songs that you don't like.The app ran fine on both my Galaxy Nexus and iPod touch, though the more songs you have, the longer it will take for the app to process your music library. On my iPod, which has over 2000 songs, the process took around 34 minutes to complete. You'll also need to be connected to the Internet while it processes your music, or else you will have to start the entire process over again. The songs only need to be processed once, so it's best to just connect your phone to your home Wi-Fi network and leave the app running while you do something else for a few minutes. (If you have a large library, it'd probably be easiest to have PaceDJ do its thing overnight.)PaceDJ may take a long time to sort through your music, but once it's finished, it may be the best app for helping you find your next favorite workout mix.Download PaceDJ for iOS ($2)Download PaceDJ for Android ($2)