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10 Vocal Zapper
CAVEATS
There are a couple of fine points. The Vocal Zapper will not work with mono
recordings, since in this case everything is center channel material. Also, any
reverb added to the vocal will tend to remain -- but in most cases, the reverb is
at a low enough level to not be objectionable (and if you're singing along with
the record, it even helps to have little remaining reverb underneath your vocal to
add depth).
It should also be noted that some recordings use vocal processing techniques
where digital delays and other enhancers spread the vocal across both
channels in unequal amounts. Luckily for us, these records are definitely in the
minority; greater than 95% of all pop, rock, and C&W records sampled during
development of the Vocal Zapper had the lead vocals mixed in the center
channel, and were therefore eligible for cancellation.
ABOUT THE CIRCUIT
Referring to the schematic, IC1 is a differential amplifier, built around a 5532 or
equivalent type dual low-noise opamp. The right channel signal couples
through C5 into the (-) input of the opamp; the left channel signal feeds either
the (-) input or (+) input of IC1, depending on the setting of S1. In the normal
mode, the left channel signal feeds the (-) input, and the IC1 acts as a simple
mixer. This produces a mono output that is the sum of the left and right
channels. With S1 in the Zap (or cancel) mode, the left channel signal feeds the
Vocal Zapper Schematic