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Dear all, Basic Q… Does anyone have insight into the optimum sweep duration using Farina's method for measuring room impulses responses? More detailed background… We are planning to make an extensive series of measurements, and in preparation have been testing the method using different sweep durations. One way to check the method is to correlate the impulses respones from repeated measurements or those generated
with different durations. To our surprise short sweeps (1-2 seconds) appear to give more
reliable results (repeated sweeps correlate, r>0.98) than longer ones. Comparing sweeps of different durations is a little trickier, because we find a temporal offset that reduces the correlation and can only be partially overcome by using cross-correlation. Nonetheless, it is apparent that durations from 1 second upwards correlate well, while going below one second leads to reliable IRs, but ones that are inaccurate when compared with those from longer sweep durations. Our surprising conclusion is that ~2s should be fine, but Farina refers to an ISO standard that
recommends very long sweeps (Farina has an example of 50s) to help overcome noise. This seems an unintuitive rationale to us, since longer sweeps should increase both the
signal energy captured and the noise energy, and the method does not involve averaging as far as I understand. Longer durations should help address brief interupting sounds, but
I am unsure if that it what was the idea. In the presence of continuous noise, we did not
notice any improvement in the IRs produced by longer sweeps. The nascent plan is to take >1 short sweep for each measurement and reject IRs that that don't correlate well with another. Any insights/advice appreciated, John.
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