Clock drift estimation and compensation for asynchronous impulse response measurements

The impulse response (IR) of an acoustic environment or audio device can be measured by recording its response to a known test signal. Ideally, the same digital clock should be used for playback and recording to ensure synchronous digital-to-analog and analog-to-digital conversion. When measuring the acoustic performance of a hardware device, be it for audio input to a device microphone or audio output from a device speaker, it is often difficult to access the device's audio signal path electronically. Therefore, the device-under-test (DUT) has to act either as a playback or recording device for the IR measurement. However, it may be impossible to synchronise the internal clock of the DUT with the reference clock of the measurement system. As a result, the recorded DUT response may be subject to unknown clock drift which may lead to undesired artefacts in the measured IR. Here, a method is proposed for estimating the drift between a playback and recording clock directly from the recorded response to obtain a drift-compensated IR. Experimental results from IR measurements of a DUT subject to clock drift indicate that the proposed method successfully estimates the drift rate and yields an accurate IR estimate in magnitude and phase.