Inside the Phone: What Makes It Tick?

Apps that Use the iPhone Microphone

Leaf Trombone, Vocoder and similar apps can sense when you sing, talk or blow into the microphone.

According to the developers of both apps, Leaf Trombone and Vocoder can interpret the intensity of a sound wave -- essentially, a vibration that moves through the molecules in air -- and then trigger a related sound. With Vocoder, for example, as you blow softly you can play a note on a piano that is equally soft, and as you blow harder the sound becomes louder. Leaf Trombone reads the sound waves and creates matching pitches depending on where you move the leaf shown on the screen. Both apps use the iPhone microphone to read the sound waves.

Leaf Trombone reads the intensity of the sound wave over the microphone.

"We are leveraging audio signal-processing algorithms to analyze the audio stream from the microphone," says Ge Wang, Leaf Trombones creator and assistant professor at the Center for Computer Research in Music and Acoustics at Stanford University. "The algorithm tracks the energy level of the audio input and conditions that signal into something that can be readily used" for blowing into the microphone.

Augmented Reality Apps Show Pop-Up Data

Augmented reality apps, such as Nearest Tube and TwittARound, can read an area around your iPhone -- using the built-in camera -- and show pop-ups that augment what you see. For example, TwittARound can show the status of nearby Twitter users, so tweeters can see which person is sending a status update.

These tools depend on several iPhone functions. According to the developer, the Nearest Tube app reads the GPS location of your phone, finds nearby train stations in London and then reads compass data and the accelerometer to find out which direction you are pointing the phone so it can then show you which way the station is. Open GL technology -- essentially a graphics engine for displaying pixels -- shows the Tube data in real-time. The app shows the overlays on top of the camera view so they look like they are pop-ups.

John Brandon is a veteran of the computing industry, having worked as an IT manager for 10 years and a tech journalist for another 10. He has written more than 2,500 feature articles and is a regular contributor to Computerworld.

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