Pocket RTA samples sounds using either internal or external microphones and then applies a Fourier Transform to the samples to obtain a frequency spectrum. The result is an accurate representation of the sampled sound broken down into its frequency components.  Please Note: When using a 1st generation iPhone the internal microphone limits the sample rate to 8KHz. Using an external microphone or headset allows up to 44KHz sample rate. The iPhone 3G does not suffer this limitation.