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-undertest (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.

Matlab sample code available at github.com/microsoft/Asynchronous_impulse_response_measurement (opens in new tab)