A method and apparatus for detection and analysis of interference and noise in a received signal within a bandwidth of a predetermined communication channel. A receiver receives a modulated signal and generates a demodulated digital baseband signal. A digital quadrature demodulator receives the digital baseband data signal and demodulates the digital baseband data signal to generate complex digital signal soft-symbol decisions at its output at the received symbol rate. A processor interface in communication with the digital quadrature demodulator and the controller transfers data between the digital quadrature demodulator and the controller. The controller reconstructs a transmitted signal from the transferred data and subtracts the transmitted signal from the modulated signal to generate a third signal representative of noise and interference underlying the transmitted signal within a predetermined communications channel containing the transmitted signal. The modulated and third signals are displayed on a computer screen or a printout.