The genius of Holzer's design is in how it overcame the limitations of a single phase shift network to shift the entire audio bandwidth. A phase shift network is composed of a resistive and a reactive circuit element, either a capacitor or an inductor. Relative values of the two will cause a phase shift(i.e. 90 degrees) at some given frequency that is easily calculated. But the amount of phase shift varies with the frequencies above or below that pass through it, relative to the intended phase shift. So a fairly consistent phase delay over the entire audio bandwidth was achieved by using multiple phase delay networks with audio bands restricted to the allowable deviation in desired phase shift versus permissible flatness of the audio response.