[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Optimal sweep duration for BRIR measurements



Dear list,

 

I've had a number of helpful replies on and off the list that have helped a good deal

with clarifying things.

 

The most significant point is the right method for establishing the level of noise. I was

presuming that noise should be observable from the correlation between successively

taken impulse responses. Though this seems plausible, it led me to the impression that

there was less noise from shortish sweeps.  In fact, one can measure the noise floor from a

single impulse response, perhaps most elegantly by using Schroeder's reverse integration

method, for which there is a clear change in the function slope when the tail of the IR

gives way to noise. Using this method,  the benefit of longer sweeps becomes much more

apparent. In a quiet office environment, the noise is about 50 dB down with a 20 s sweep,

whereas it is only about 35 dB down for a 2 s sweep. So the noise rejection improves with

sweep length, but is still pretty good even with a short one. Correlation also has the

problems that offsets in time can lead to a drop in value, which cannot easily be compensated

(cross-correlation will not help unless the delay is an integer number of sampling periods),

and that one has to take more than one measurement to do the correlations.

 

John.

 

 

 

Prof. John Culling

School of Psychology, Cardiff University

Tel: +44 (0)29 2087 4556

Yr Athro John Culling

Yr Ysgol Seicoleg, Prifysgol Caerdydd

Ffôn : +44 (0)29 2087 4556