CLIOwin 6.5 PCI User's Manual - Audiomatica Srl

11.3.3 GATING
Enabling Gating allows quasi anechoic Frequency Response to be carried out in normal
environments, with obvious and less obvious limitation. Regarding the geometrical
environment required, Sinusoidal analysis does not differ from what has been said
about MLS. Nevertheless the latter give a much more intuitive approach. It is strongly
suggested to 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 intuitive grasp. Fig.11.4, repeated from the
MLS chapter, show a typical setup, while Fig.11.5 shows what really happens, using as
stimuli a 20ms 1kHz Sinusoidal Burst.
SPEAKER
DIRECT SOUND
70 cm - 2.03mS
MIC
FIRST REFLECTION
250 CM - 7.26mS 120 cm
ABSORBING MATERIAL
FLOOR
Figure 11.4
0.020
CLIO
V
0.012
0.004
-0.004
-0.012
-0.020
0.00 2.0 4.0 6.0 8.0 10.0 12 14 16 ms 18 20
Figure 11.5
The time of sound fly is clearly visible at the beginning, roughly 1.3ms. This is the value
users should input in the Delay Edit Box. Thereafter is a short time the device takes to
start. This is usually short enough to not affect amplitude evaluation but adversely affect
distortion measurements. At 7 and 8 ms, where there are two consequent sinusoid
positive peak, a level increase is clearly visible. This is the effect of the first reflection
(floor); it affects amplitude evaluation which therefore should have stopped before. The
time the system evaluate the signal is usually defined as Meter On time. This is
112 Chapter 11 - Sinusoidal