Omnia .9 Installation & User Manual page 193

SYSTEM MENU
30 Hz Phase Invert produces a 30 Hz sine wave which abruptly changes phase twice per second. This test tone allows you
♦
to verify DC coupling of Omnia.9's composite output (with an external oscilloscope), as well as your exciter and your
modulation monitor. Many exciters and even more modulation monitors have inaccurate low frequency response, which
will cause severe over-modulation (or erroneously display severe over-modulation) if the low frequencies abruptly
change, such as is customary in music that contains kick drums (which most songs do!).
Bessel Null 31,187.6Hz allows you to set exact +/- 75kHz modulation with a direct off-air spectrum analyzer.
♦
Omnia.9 provides extremely tight modulation control. Your modulation monitor's meter should essentially stand still at +/-
75kHz. (The composite meter in Omnia.9 will stand still at 75kHz no matter what any external equipment is doing). If it does
not, lack of DC coupling is a likely culprit. To test for this, follow these steps:
Connect an Oscilloscope (making sure it is DC coupled, not AC coupled) to Omnia.9's composite output.
♦
Select 400 Hz. Adjust the oscilloscope input level to accurately reach a particular set of lines.
♦
Select 30 Hz. Verify that the peaks reach the same lines at the exact same spot.
♦
Select 30 Hz Phase Invert. Verify that the peaks reach the same lines and never overshoot. For a "control sample", set your
♦
oscilloscope to AC coupling, and watch the waveform bounce.
We have now verified that Omnia.9's composite output is exactly accurate. You may also try the other test tones as well as
program audio.
Here is another test, this time checking for overshoots:
Connect Omnia.9's composite output to your exciter and look at your modulation monitor.
♦
Select 400 Hz and adjust for exactly 100% modulation.
♦
Then select 30 Hz and verify that you are reaching the same modulation level.
♦
Finally, select 30 Hz Phase Invert.
♦
You will likely see some overshoot, but if you see more than a percent or two, then either your exciter (or STL) is causing the
overshoots OR your modulation monitor is displaying overshoots that are not there. In extensive field testing, this problem has
proven to be much more common than we ever thought! Please note that this problem affects every processor, but it has just
never been as easy to pinpoint as it is now due to the presence of Omnia.9's built in signal generator.
CHAPTER 23 |
176