Complete feedback phaser built from scratch
An elaboration of the phaser algorithm to include a feedback path around the time-varying allpass filter. The feedback
enhances the phasing effect.
The heart of this phaser algorithm is the Controllable 2-pole allpass filter whose frequency response has a flat magnitude
spectrum but a nonlinear phase response. When the allpass filter is connected in parallel with the original dry signal (via the
Linear Mixer), the net effect is a notch filter. The key to achieving the classical "phaser" effect is to vary the allpass filter
coefficients in time, such that the notch filter varies in time. The Controllable 2-pole allpass block is designed for this
purpose. The first Control Input is the instantaneous centre frequency of the notch (when the parallel dry branch is
connected), and the second Control Input specifies the instantaneous bandwidth of the notch. In this example, the centre
frequency is driven by the Exponential Sweep Control Generator which generates a control signal (in Hz) which sweeps
exponentially in time across a desired frequency range. The bandwidth of the notch is made to be equal to a constant
fraction of the centre frequency (achieved using the Constant Control Generatorr and the Multiply Controls blocks).
The limiter ensures that the output doesn't cause digital clipping arising from constructive interference of the dry signal with
the notched signal.
You can experiment with different types of sweep signal for both the centre frequency and the notch bandwitdh. (The
exponential sweep demonstrated here just happens to be a common phaser implementation).
Try changing all parameter settings of all components to achieve a wide range of interesting feedback phasing effects.
