Re: Optimal sweep duration for BRIR measurements

["Menzies-Gow R.D." <D.Menzies@xxxxxxxxxxx>]

Variations in measured BRIR could be due to anything changing in the room – e.g. drafts, convection from heaters, people moving. Shorter sweeps are less affected by this, but more effected by signal noise. Could also be head movement if measuring live subjects.

Did you check the stability of the convolver by convolving the sweep with the inverse? Could also try first convolving the sweep with a test signal.



--
Dylan Menzies
Senior Research Fellow
Institute of Sound and Vibration
University of Southampton, UK





On 24 July 2015 at 16:25, John Culling <CullingJ@xxxxxxxxxxxxx<mailto:CullingJ@xxxxxxxxxxxxx>> wrote:
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.

Prof. John Culling
School of Psychology, Cardiff University
Tel: +44 (0)29 2087 4556<tel:%2B44%20%280%2929%202087%204556>

Yr Athro John Culling
Yr Ysgol Seicoleg, Prifysgol Caerdydd
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