946 Chapter 25
the parameters of the channel to their stored values).
Eyeball comparison and human tweaking is the reset-
ting mechanism employed. The comparison is between
a recalled value displayed on a meter, LED column, bar
display, null indicator, or up on a GUI (Graphical User
Interface) screen, and the immediate real value read
from the control in question and displayed on an adja-
cent display. As the relevant control is tweaked, its indi-
cated value will be higher or lower than the stored
value; when the two are matched, then the control posi-
tion is the same as it was when the snapshot was taken.
Fig. 25-115 shows in simplistic form the basis of the
matching process.
GUI displays are presently the easiest way of
performing this matching. So much information is
visible at once, which is a blessing in this circumstance.
Even with increasingly common totally program-
mable/recallable consoles, screen-based display of
control statuses is a very useful function, if in addition
to localized feedback to each individual control. It looks
good, too.
25.16.9 Nulling
Null indicators are particularly easy to implement and
use. They usually take the form of a pair of LEDs adja-
cent to the relevant control. If the real value is higher
than the recalled value, the upper LED lights; if it is
less, the lower one lights. If they both come on, the two
values are matched. Even simpler nulling indicators
take the form of a single LED that only comes on (or
alternatively goes out) when the two values match. A
nicer arrangement is a single-cell green/red LED giving
an unequivocable “go” or “no go” indication. This
device makes it particularly easy to spot anything out of
order on a channel.
A fairly elaborate demultiplexing system has to be
plumbed onto the channel board, however, to deliver the
software-derived nulling indications to the front-panel
LEDs; Fig. 25-116 is representative. A further amount
of processor memory area needs to be dedicated for this
output facility in addition to that already spoken for by
the input multiplexing.
Another software consideration when using null
indicators is that the chance of actually finding the 1 in
256 position that is correct is pretty slim. Reducing the
effective resolutional accuracy to fewer bits can make
the operation a lot simpler. The accuracy of the recall
system can easily outstrip that which it is monitoring
and it is a judgment call between resetting precision and
the ease of so doing.
As laborious as these facilities may be operationally,
a complete reset of console parameters can be achieved.
It is considerably less laborious and inaccurate than
writing everything down.
Interestingly enough, any bus-slew inaccuracies
engendered on storage tend to be canceled during recall.
When all the controls on a channel are reset at or close
to their original settings, all the bus errors will be very
similar to those present when stored.25.16.10 Resetting FunctionsThe next logical step in developing computer assistance
is for the machine not only to remember console
settings but also to reestablish the console to its
previous operational state on command. This means that
if the multitrack routing on channel 27 was going to
machine track 15 when the console status was stored,
then regardless of what has happened or how the
routing may have altered or configurations changed,
upon recall channel 27 will go to track 15.
Most of the circuitry described in this chapter, espe-
cially the multitrack console example, is from a genera-
tion of design where active resetting of all major
switched functions was a requirement. Variable controls
were not even considered as candidates for resettability
since it demanded too great a shift in technology. As we
will see, the techniques necessary for that become
instrumental in a deeper, broader change of console
design, structure, operation, and philosophy.
Every switched function that is intended to reset
needs to be made electronically controllable; the tech-
niques are detailed in earlier sections. This replacement,
by and large, has already been implemented with other
ends in mind, such as simplifying PC layouts, avoiding
large physical switches, and, not the least, facilitating
some of the tortuous signal rerouting required in a
modern production console.
In addition to the data acquisition system as just
described (i.e., switches to computer), a second digital
distribution system—computer to switches—is
required. Techniques similar to those described for
nulling indication work well.25.16.11 Motorized Pots and FadersMotorized pots and faders look and feel like conven-
tional ones, only a clutched motor drive controlled by a
servo allows the mechanics to be reset to any point on
their travel. A rider track, either a normal resistive track
encoded by an A/D converter or a digital track direct
input allows a microcontroller to keep track of the posi-