Real-time Analysis

SignalScope Pro for iPhone OS devices is a real-time analysis toolset, suitable for use in areas such as acoustics, audio, electronics, and vibration. SignalScope Pro includes 3 tools for time or frequency domain signal analysis, including an FFT-based narrowband spectrum analyzer, a fractional octave band (whole and third octave) spectrum analyzer (traditionally referred to as an "RTA"), and an oscilloscope (waveform analyzer).

Input signals can be acquired from the built-in accelerometer, or from the current audio input path (the iPhone OS automatically selects the audio input path according to which external audio devices, if any, are connected to your device).

Tools

• The FFT analyzer performs narrowband spectrum analysis of one to three input channels (depending on the input device and channel configuration).
• The fractional octave band analyzer (RTA) performs whole or third octave spectral analysis on a single input channel (only when the sample rate is 48 kHz).
• The level meter operates as a sound level meter, or as an rms signal level meter.
• The oscilloscope can display time waveforms for one to three input channels (depending on the input device and channel configuration).

Each tool includes manual and automatic plot scaling, as well as a data cursor for obtaining precise signal information. Additionally, the current data in each tool can be saved to a tab-delimited text or MAT file. The analyzer display can also be saved to an image file within the device's photo library. (The image can later be retrieved from the built-in Photos app.)

Audio Input Path

The audio input path is automatically determined by the iPhone OS, according to the external audio hardware, if any, connected to your device. Some possible audio input and output scenarios are discussed on the audio routes help page.

On all devices, except the 1st generation iPhone, the audio input data is sampled at 48 kHz. On the 1st generation iPhone, the sample rate will be limited to 8 kHz when using any one of the built-in microphone, built-in speaker or receiver (the receiver is the internal speaker that is located near your ear when using the iPhone as a phone).

The three typical audio input paths are discussed in greater detail on the following pages:

• Built-in Microphone (iPhone only)
• Headset Input (not available on 1st gen iPod touch)
• Dock Input

Built-in Accelerometer

The built-in accelerometer signals are sampled at nominally 100 Hz, which limits the available signal bandwidth to nominally 50 Hz.

The built-in accelerometer includes three input channels--one for each axis of acceleration, which are defined as follows, with the device oriented such that you are facing the screen with the dock connector toward the bottom.

• X -- Positive acceleration is toward the right side of the screen.
• Y -- Positive acceleration is toward the top of the screen.
• Z -- Positive acceleration is out of the front of the screen, toward you.

Apple does not recommend using the internal accelerometer for making precise measurements.