A hearing aid comprising memory means for storing preset signal processing parameters, and adjusting means for the stepwise adjustment of one or more of the stored signal processing parameters from a starting point of a predetermined range to an end point of said range. Examples of signal processing parameters to be adjusted are high tone amplification, maximum output level and noise suppression threshold value. Examples of providing the trigger signals include: a time clock, repeated turning on of the hearing aid, repeated placing of a battery and repeated operation of a knob. The hearing aid may be arranged for mutual communication with an external unit. The external unit may include selection means for the setting in the adjusting means of the one or more parameters to be adjusted, range setting means for the setting in the adjusting means of the range of the one or more parameters to be adjusted, step magnitude setting means for the setting in the adjusting means of a step magnitude to be used in said setpwise adjustment, and interval setting means for the setting of the repeat interval of the successive trigger signals in the time clock. The hearing aid carries out the adjustment autonomously in inaudible steps.