Impulse Response Measurements in the Presence of Clock Drift

There are many impulse response measurement scenarios in which the playback and recording devices maintain separate unsynchronized digital clocks resulting in clock drift. Clock drift is problematic for impulse response measurement techniques involving convolution, including sinusoidal sweeps and pseudo-random noise sequences. We present analysis of both a drifting record clock and playback clock, with a focus on swept sinusoids. When using a sinusoidal sweep without accounting for clock drift, the resulting impulse response is seen to be convolved with an allpass filter having the same frequency trajectory form as the input swept sinusoid with a duration proportional to the input sweep length. Two methods are proposed for estimating the clock drift and compensating for its effects in producing an impulse response measurement. Both methods are shown to effectively eliminate any clock effects in producing room impulse response measurements.