Abstract: A multi-variate system having a microprocessor-based telecommunications interface which has a digital adaptive all-pass filter and automatically variable delay distortion equalization circuitry which in combination provide both pre and post delay distortion equalization on the transmit and receive sides of bidirectional data lines (or dedicated telephone lines), which interfaces a conventional 4-wire analog facility and a data station termination at the customer premises equipment. A method of practicing the preferred embodiment of the invention is also disclosed.