1380 Chapter 35
At first the unprocessed output of the DUT (raw
data) is recorded and stored on the PC hard disk. Based
on this original data set, the corresponding processing
algorithm including band pass filters or time windows
can be used multiple times with different parameters to
look at the parts of interest.
A simple way to calculate the transfer function H(Z)
from the recorded raw data is to divide the measured
frequency response Y(Z) by the frequency response of
the signal X(Z) (or by a reference response that was
previously measured). The impulse response h(t) can
then be computed using the inverse Fourier Transform.
Until now it is common to utilize a static measuring
procedure where the impulse response is derived in a
separate step after every acoustic measurement. In
contrast, a newly developed, dynamic method allows
one to measure room acoustic impulse responses (RIR)
in an efficient manner and to analyze this way the
acoustic properties of an investigated acoustics space
very user friendly—i.e., in real time,^57 see Fig. 35-57.
Determining the impulse response in real time means
in this respect that gathering the acoustic source signals
and calculating the impulse response data are a simulta-
neous and continuous process.
The dynamically derived RIR is because of a number
of optimized postprocessing steps qualitatively abso-
lutely equivalent to a statically derived RIR and may
have typical lengths of 4–10 s.
The transformation between the frequency and time
range is linear and of full length, analogous to the static
procedure. Averaging can be likewise used to suppress
the noise.Figure 35-53. SPL mapping in simulation programs.
A. 2D presentation in CATT acoustics.B. Narrow band presentation in EASE 4.0.C. Broad band presentation in ULYSSES 2.3.Figure 35-54. RaSTI presentations in simulation programs.B. 3D presentation in a concert hall.A. 3D presentation in a mosque.