A test system emulates the analog processing portion of a communication device and adjusts input signals based on distortions specified by a user and control signals generated by a baseband processing portion of the communication device. The distortions can be specified in terms of the baseband. One or more of the control signals can be bypassed to investigate the effect of each of the control signals alone, or in various combinations. An operator interface can be provided that allows the user to set up and conduct the tests, and monitor the results. Facilities are also provided to allow the reference voltage at the baseband processing portion to be adjusted while maintaining the appropriate reference voltage for components in the test system.