Recording Consoles 793energy!) so that electronically balanced input stages are widely employed instead. These
aim to confer all the advantages of a transformer cheaply, quietly, and on a small scale. To
some degree, an electronic stage can never offer the same degree of CMR, as well as the
complete galvanic isolation, offered by a transformer.
27.7 Mixer Automation .................................................................................................
Mixer automation consists (at its most basic level) of computer control over the individual
channel faders during a mixdown. Even the most dexterous and clear thinking balance
engineer obviously has problems when controlling perhaps as many as 24 or even 48
channel faders at once. For mixer automation to work, several things must happen. First,
the controlling computer must know precisely which point in the song or piece has been
reached in order that it can implement the appropriate fader movements. Second, the
controlling computer must have, at its behest, hardware that is able to control the audio
level on each mixer channel, swiftly and noiselessly. This last requirement is fulfi lled a
number of ways, but most often a voltage-controlled amplifi er (VCA) is used.
A third requirement of a fader automation system is that the faders must be “ readable ” by
the controlling computer so that the required fader movements can be implemented by the
human operator and memorized by the computer for subsequent recall.
A complete fader automation system is shown in schematic form in Figure 27.23. Note
that the fader does not pass the audio signal at all. Instead the fader simply acts as a
potentiometer driven by a stabilized supply. The slider potential now acts as a control
voltage, which could, in theory, be fed directly to the voltage-controlled amplifi er,
VCA1. But this would miss the point. By digitizing the control voltage, and making this
value available to the microprocessor bus, the fader “ position ” can be stored for later
recall. When this happens, the voltage (at the potentiometer slider) is recreated by means
of a DAC and this is applied to the VCA, thereby reproducing the operator’s original
intentions.
One disadvantage of this type of system is the lack of operator feedback once the fader
operation is overridden by the action of the VCA; importantly, when in recall mode,
the faders fail, by virtue of their physical position, to tell the operator (at a glance) the
condition of any of the channels and their relative levels. Some automation systems
attempt to emulate this important visual feedback by creating an iconic representation
of the mixer on the computer screen. Some even allow these virtual faders to be moved,