produces phase quadrature signals from an audio input.The Hilbert transform produces phase quadrature signals from an audio input. This basically boils down to the creation of two output signals which are exactly 90° out of phase. A frequency shifter is made by using these signals as the (real, imaginary) complex number input to complex-mod~. hilbert~ was originally part of the library. Together with complex-mod~, hilbert~ is the heart and soul of the fshift1~ frequency shifter.