Audio Routes

Audio Input Path

The audio input path is automatically determined by iOS, according to the external audio hardware, if any, connected to your device. Some possible audio input and output scenarios are discussed below.

On all iOS devices, the audio input data is generally sampled at 48 kHz. Some audio input accessories may operate at lower sample rates, such as 44.1 kHz. SignalScope allows the sample rate to be manually set, which means that, depending on the hardware, the rate may be set much lower (e.g. 8 kHz) or much higher (as high as 192 kHz on some devices).

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

Prefer Speaker Output

  • This option enables the built-in speaker of an iPhone to be used for audio output instead of the receiver (the small speaker near the top of the iPhone that is used when making phone calls).

Built-in Accelerometer

Regardless of the active audio route, the internal accelerometer may be selected as the current input device in SignalScope.

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 relying on the internal accelerometer for making precise measurements.