CLIOwin 7 PCI User's Manual - Audiomatica

it is necessary to remove the flight time plus the device settling time; this can be easily
accomplished setting the internal trigger delay, in FFT settings, to 1.5ms; the final result
shown is shown in 11.11 and permits the identification of the device harmonic distortion.
To proceed further one could vary the stimulus amplitude and test the distortion of the
tweeter at different amplitudes; using bursts also prevents the damage of the unit as
the overall power delivered to it rather low and a direct function of the duty cycle of the
burst itself.
The main application of RTA analysis is in assessing the quality of an audio installation
(from the placement of the speakers in a listening room to the overall sound quality of
a car stereo system). In these cases pink noise is often used as the stimulus. If you
are not using CLIO as the source of such a stimulus be sure to use a good one; you
may find several audio generators that do the job, but they are usually expensive. A
good choice is to use a recorded track of one of the various test CDs available; in this
case not all the CD-ROM readers may furnish adequate results, as appears from the
graph in Fig.9.3
0.0
CLIO
dBV
-20.0
-40.0
-60.0
-80.0
-100.0
20 100 1k Hz
10k 20k
Figure 9.3
All three graphs represent true analog pink noise, they are played at intervals of 5dB
for clarity. The upper (red) is the output of an Audio Precision System One generator;
the second (blue) is the pink noise of track 4 of the Stereophile Test CD played by a
Philips CD692 CD player, the third is the same track of the same test CD output by the
computer which I'm writing with right now (Pioneer DVD Player plus Crystal Sound
Fusion PCI Audio).
When taking RTA measurements use, at least, 16k FFT size if you want to cover
the entire 20-20kHz audio band; using lower sizes results in octave bands not
present as no FFT bins fall inside them.
100 Chapter 9 - FFT