Transfer Function Measurements When the Reference Signal is Known but not Accessible

Transfer function measurements offer significant benefits over historical band spectrum measurements for calibrating loudspeakers by additionally calculating phase and coherence in the frequency domain and identifying the arrival time of reflections in the time domain. However, this requires two channels: the reference signal input to the speaker and a microphone in the sound field. In cinema systems, it is often difficult to duplicate the reference signal to an analyzer. There may be no spare inputs or outputs, limited routing options, and/or digital connectors not conducive to a Y-cable. A virtual reference method is presented, which, given a copy of the reference signal, can be reconstituted in real-time. Virtual reference can also detect, measure, and compensate for sample rate differences between the playback device and the analyzer. This allows the analyzer to show a stable trace while virtual reference separately displays clocking differences such as jitter and wander.