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distracting while reading the text, click the red STOP button to freeze
it. It will resume operation wherever it left off if you click START.
Vector diagram showing how the addition of two signals whose amplitudes
are varying in opposition and whose phase differs by 90° produce
a signal that continuously varies from 0° to -90° and back
again.
The constantly changing arrows on the
X and Y axes represent the two signals, phase A and phase B that are
90° apart as they are shown by their physical placement in the
diagram. The third arrow that rotates forward and back through 90°
represents the composite signal, which will have a true, pitch-varying
vibrato.
If for some
reason, the amplitude of one of the two phases is different from that of the
other, this will also introduce a volume-varying tremolo into the tone as
well as the pitch varying vibrato. In these older instruments where there
can be considerable component parameter changes with time, this is indeed
the case. It is also somewhat true even when these instruments were new as
it would be very difficult to balance the outputs of the phase splitter over
the entire frequency range of the instrument. But the presence of some amplitude-varying
tremolo in the signal, as long as not excessive, is not bad by any means.
The above diagram clearly shows how the composite signal varies between
0° and -90° as the two input signals vary in amplitude. On the
next page there is a diagram of the final result, the same electrical
signal which now has the vibrato applied. The gradual changing of the
length along the x axis of the wave shows that its instantaneous frequency
is changing. This is the result of combining the gated signals of phases
A and B.