Graphic Delay Equalizer
Jussi Rämö, Vesa Välimäki · 2019
A graphic delay equalizer based on a high-order nonparametric allpass filter design is proposed. Command points at the centers of octave frequency bands are connected with polynomial interpolation to form a continuous target group-delay curve as function of frequency. The required number of all-pass sections depends on the area under the target curve. The group-delay area at low audio frequencies is small due to the linear frequency scale, so only a few allpass sections can be assigned there, which reduces the accuracy. Design accuracy can be improved by adding a constant delay to the target curve, which increases the area. Two use cases are presented: the group-delay equalization of a multi-way loudspeaker and the linearization of the phase response of a regular magnitude-only graphic equalizer. The graphic delay equalizer can be used to enhance the perceptual quality of audio systems or to produce audio effects.