I can hear feedback, how can it be turned off?

You may experience feedback when connecting speakers and microphones to your sound card. This is because the sound card may patch the signal present on the input to the output. If the WinMLS mixer is used (set in Measurement-> Sound Card Settings…), this should be avoided by making sure is checked under Advanced Settings in Measurement->Sound Card Settings….

If the WinMLS mixer is not used, the feedback is not just annoying but can affect the measurements as well, Feedback is detected as false echoes in the impulse response and as comb filtering in the frequency response. The unwanted feedback can be turned off using the Windows sound card mixer. The setting in the Windows sound card mixer that gives the feedback has different names depending on the sound card. If you mute all inputs and outputs that you are not using for the measurement signals the feedback should be damped. See the chapter If your Sound Card does not support the WinMLS Mixer in the WinMLS2000 User’s Guide for more information.