Select this if you want to measure an input signal such as background noise, a sinusoid or an impulsive signal.
If you want to measure the impulse or frequency response using a source (typically a loudspeaker), you should instead select the choice found below on the list.
But if you wish to measure the impulse response using a short pulse, e.g. a balloon burst or a gun shot you should use the option.
The dialog shown below is displayed.
Click the button to display the more advanced settings shown below.