User`s manual

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
Audiomatica Srl FFT - 1/3 OCTAVE 08/07/2001 9.33.29
CH A dBV 51.2kHz 16384 Hanning File:
100 1k 10k 20k20 Hz
0.0
dBV
-20.0
-40.0
-60.0
-80.0
-100.0
CL IO
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.
106 9 FFT, RTA AND “LIVE” TRANSFER FUNCTION