Recording Consoles 769signal will create a single vertical line, and an out-of-phase mono signal will produce
a horizontal line. A stereo signal produces a woolly ball centered on the origin; its
vertical extent is governed by the degree of L/R correlation and its horizontal extent
is governed by L/R decorrelation. And herein lies the polar display’s particular
power, that it can be used to assess the character of a stereo signal, alerting the
engineer to possible transmission or recording problems, as illustrated in
Figure 27.5.
One disadvantage of the polar display methodology is that, in the absence of
modulation, the cathode ray will remain undeviated and a bright spot will appear at
the center of the display, gradually burning a hole on the phosphor! To avoid this,
commercial polar displays incorporate cathode modulation (k mod) so that, if the signal
goes below a certain value, the cathode is biased until the anode current
cuts off, extinguishing the beam.
LRRLLRLRRLLRLRRLLRLRRLLRLRRLLRLRRLLRRight Left MonoOut of phase Narrow stereo Wide stereo
Figure 27.5 : Audio polar displays.