A feedback based active noise reduction system comprising: a feedback loop having an audio path segment, a feedback component for forming at least part of the feedback loop, the feedback component including a first signal input for accepting an audio input signal, a driver output for providing a driver signal to a driver of the audio path segment, a first feedback input for accepting a first feedback signal from a first sensor responsive to a signal on the audio path segment, a control parameter input for accepting a control parameter for adjusting at least one of a gain characteristic and a phase characteristic of the feedback loop, an adjustable feedback factor including the control parameter input, and an instability detector for detecting an instability condition in the feedback component and forming the control parameter based on a result of the detection, the instability detector including a feedback loop signal input for accepting a feedback loop signal, an audio signal input for accepting the audio input signal, a circuit for detecting an oscillatory signal component in the feedback loop signal not represented in the audio input signal, the circuit including: a circuit for forming a modified feedback loop signal, the circuit including circuitry for removing a component of the audio input signal from the feedback loop signal, a circuit for detecting the oscillatory signal component in a specified frequency range in the modified feedback loop signal and for delivering a detection output that is dependent on a result of said detecting, a gain controller for modifying the control parameter depending on the detection output, and a control parameter output for providing the modified control parameter to the control parameter input of the feedback component, wherein the adjustable feedback factor is arranged for being adjusted, based on the modified control parameter, to modify a bandwidth of the gain characteristic of the feedback loop. a feedback loop having an audio path segment, a feedback component for forming at least part of the feedback loop, the feedback component including a first signal input for accepting an audio input signal, a driver output for providing a driver signal to a driver of the audio path segment, a first feedback input for accepting a first feedback signal from a first sensor responsive to a signal on the audio path segment, a control parameter input for accepting a control parameter for adjusting at least one of a gain characteristic and a phase characteristic of the feedback loop, an adjustable feedback factor including the control parameter input, and an instability detector for detecting an instability condition in the feedback component and forming the control parameter based on a result of the detection, the instability detector including a feedback loop signal input for accepting a feedback loop signal, an audio signal input for accepting the audio input signal, a circuit for detecting an oscillatory signal component in the feedback loop signal not represented in the audio input signal, the circuit including: a circuit for forming a modified feedback loop signal, the circuit including circuitry for removing a component of the audio input signal from the feedback loop signal, a circuit for detecting the oscillatory signal component in a specified frequency range in the modified feedback loop signal and for delivering a detection output that is dependent on a result of said detecting, a gain controller for modifying the control parameter depending on the detection output, and a control parameter output for providing the modified control parameter to the control parameter input of the feedback component, a circuit for forming a modified feedback loop signal, the circuit including circuitry for removing a component of the audio input signal from the feedback loop signal, a circuit for detecting the oscillatory signal component in a specified frequency range in the modified feedback loop signal and for delivering a detection output that is dependent on a result of said detecting, a gain controller for modifying the control parameter depending on the detection output, and a control parameter output for providing the modified control parameter to the control parameter input of the feedback component, wherein the adjustable feedback factor is arranged for being adjusted, based on the modified control parameter, to modify a bandwidth of the gain characteristic of the feedback loop.