A directional hearing aid comprises a front microphone (11) and a back microphone (12), a delay processor (13, 14) for processing, according to a control parameter, the respective microphone signals, and means (8a) for adjusting the control parameter in order to minimize the output signal from the delay processor. The control parameter may be adjusted to change smoothly the function mode of a hearing aid between omnidirectional mode, a directional mode and a directional mode with a pair of null directions, symmetrical about the 180 direction. The directional controller may be implemented in a multichannel version. The invention provides a hearing aid, a method of controlling a hearing aid, a noise reduction system and a method of reducing noise in a hearing aid.