User`s manual

11.4.3 GATING
Enabling Gating allows quasi anechoic Frequency Response to be carried out in
normal environments, with obvious and less obvious limitations. Regarding the
geometrical environment required, Sinusoidal analysis does not differ from what
has been said about MLS. Nevertheless the latter gives a much more intuitive
approach. It is strongly suggested that you become very familiar with quasi
anechoic measurements using MLS before dealing with Gating. What follows is a
brief description of the parameters involved. We are going to use some figures to
help our understanding. Fig.11.4, repeated from the MLS chapter, shows a typical
setup, while Fig.11.5 shows what really happens, using as stimuli a 20ms 1kHz
Sinusoidal Burst.
Figure 11.4
Audiomatica Srl FFT 29/06/2001 17.36.50
CH A dBV 51.2kHz 4096 Rectangular File: gating1.fft
0.00 2.0 4.0 6.0 8.0 10.0 12 14 16 18 20ms
0.020
V
0.012
0.004
-0.004
-0.012
-0.020
CL IO
Figure 11.5
The time of the sound propagation delay is clearly visible at the beginning, roughly
1.3ms. This is the value users should input in the Delay Edit Box. Thereafter is the
short time that the device takes to start. This is usually short enough to not affect
amplitude evaluation but adversely affects distortion measurements. At 7 and 8 ms,
where there are two consequent sinusoid positive peaks, an increase in level is
clearly visible. This is the effect of the first reflection (floor); as it affects amplitude
148 11 SINUSOIDAL