a circuit added in cascade with a filter having a characteristic, which, when combined with that of the filter, produces an overall ' flat ', or equiripple group delay characteristic. Its job is made harder (higher order required) if the group delay characteristic of the filter has a large 'spike' in it. This will typically (always?) occur at the passband edge, and is particularly severe in the case of an elliptic filter. The term 'allpass' implies that the amplitude response of the equalizer is constant - it passes all frequencies equally - and so there is no modification to the amplitude response of the filter. ~~~~~ go back with your browser back button. If lost, go home