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Unity Gain 89
VeniceU
Operator Manual
Unity Gain
Unity gain is a gain of 1, that is, no gain or attenuation is applied to a signal.
If a signal entered a mono line level input of the VeniceU at 0dBu and the gain was set
to +10dB (an internal 10dB attenuation sets the net gain to 0dB), then the signal was
routed to each output at 0dB, the channel fader was set to 0dB and each output fader
was set to 0dB, the output should be 0dBu (or unity). Some console manufacturers
mark the 0dB level of their faders and pots ‘U’.
Simple. But that’s just one signal. If we have two 0dBu signals entering the VeniceU
(assuming they are coherent, that is, the same level and phase) to be summed in the
buses, the output would no longer be 0dBu.
Simply,
0dBu = 0.775 volts
0.775 volts + 0.775 volts = 1.55 volts
1.55 volts is 0.775 volts +6dB (or a gain of 2)
To retain an output of 0dBu (our previous unity level) each input must be reduced.
0.775 volts / 2 = 0.3875 volts
0.3875 volts is 0.775 volts -6dB (or a gain of 1/2)
So, each fader must be reduced to -6dB to retain the unity gain level of 0dBu on the
console output. When using four inputs at 0dBu, the faders must be reduced to -12dB.
Real life signals are not continuous, but the principle is the same. If you have a
sinusoidal input that is nominally 0dBu on all 32 inputs with the channel faders at 0dB,
the output is likely to be well above the 21dBu maximum output of the console and
leave no headroom spare. With real world signals, 32 channels summed together will
give around 6dB to 9dB gain because it is unlikely that all 32 channels will receive the
same signal at the same time. Instead, signals will occur at different times, and there
will be cancellation due to phase and frequency differences.
Signal Processing and Amplifiers
The final links in the system tend to be graphic equalisers, loudspeaker processors and
finally amplifiers and speakers.
Graphic equalisers have the same problems as the VeniceU’s EQ. If excessive boost is
applied to the signal, the graphic equaliser’s output may be overloaded. If the output
of the VeniceU is higher than the maximum input level of the graphic, the input of the
graphic may be overloaded.
Loudspeaker processors have similar problems. If the input level to the processor is too
high, the input may be overloaded and introduce distortion into the outputs (and to the
speakers!). In addition to this, any boost on the processor’s outputs (say you want 3dB
more bass) will cause that output to overload earlier (in this case 3dB before the other
outputs).
Finally, amplifiers can introduce the most interesting results.
An amplifier has a sensitivity. That is, an input signal level that causes the amplifier to
produce its maximum output level. For many amps this is 0dBu (0.775 volts RMS),
while others use 0dBV (1 volt RMS) and others use different levels. Beyond this
sensitivity, the amplifier’s output will not be able to produce any more power and ‘CLIP’
(usually indicated by some serious looking red lights). Sending +21dBu level from the
VeniceU will clip the output of most amplifiers causing damage to your loudspeaker
system.