The limiter has a fixed threshold of +20dBu so will not become active unless the output level reaches this (it's purpose is to prevent overload of the optional A/D converter so the 'active' LED should not be lighting under normal recording situations). The limiter comes after the output level control in the signal chain. To test whether the limiter is working properly or not you need to measure the output of the limiter by looking at the INT LED meter. Make sure the 'bypass' button is pressed in so that no processing on the unit is active. Now when the limiter is engaged and you set the input gain and output fader so that the output signal level goes above +20dBu you should see the 'Active' LED come on and the LED meter reaching 0 but not 'O/L'. Then if you disengage the limiter the 'Active' LED will turn off and the 'O/L' LED will light on the LED meter. If this is not happening then ensure that the output level is high enough for the limiter to become active. If you suspect that the limiter is faulty then please contact us for further support.