948 Chapter 25
If the clock is triggered by the rising edge of the A train
and the B train is active, then the latch output goes high,
indicating one direction of rotation (left to right in Fig.
25-117). In the other direction, the rising clock edge
from A corresponds to B being inactive, so the latch
output goes low.
It is rather a simplistic circuit that assumes that the
making contacts of the resolver are perfect and no false
triggering will occur. With more swanky optical
resolvers this may be true, but with mechanical ones a
little debounce clean up prior to the D-latch gates may
be advisable.
25.16.13 Control Surfaces
A large problem with recording and live consoles has
been precisely that—they’ve gotten large. Console
channels have grown into long, thin strips for purely
historical reasons, and the manufacturing technique of
hanging all the signal-path electronics on acres of dense
PC card has just tagged along with little evolution.
Removing the audio electronics (analog or digital) from
the control surface into a remotely controlled equipment
rack seemed quite an obvious development, although
until recently it was a technically unwieldy one. Many
types of analog circuits lend themselves to direct
remoting. For example, VCAs for level control need, in
essence, a single dc control line. Others, such as equal-
izers and microphone preamplifiers, don’t. Noise and
difficulties in extending nonzero-impedance configura-
tions are both significant problems. As with everything
else, these areas of difficulty look quite different given a
dose of digits. As has been seen, with only minor
compromises, digitally controlled remotable audio
circuits of all sorts are realizable at some cost and
complexity; it is entirely possible for the control surface
to become now just that, no audio need go anywhere
near it.
The question of whether the control surface and
signal processing electronics should be divorced and
live in environments possibly better suited to them is a
more vital one with digital mixers than with analog;
although possible, it was (is) actually very expensive to
do remote, fully digitally controlled analog (DCA)
circuitry that sounded decent and wasn’t riddled with
clicks, burps, and fizzies. It is more expensive now,
amusingly, than having a fully digital signal path, which
has really sorted that argument out once and for all.25.16.13.1 The Single Channel ConceptThere is an immediately apparent redundancy with large
consoles—rows and rows of identical channel modules.
The first intuitive step would be to reduce all those to
just one set of channel controls that is selectable or
assignable to any channel that needs tweaking. The first
modification to this rather simplistic single-channel
console concept is that the main level faders need to be
kept continuously available in front of the operator; a
button adjacent to each of the individual faders (the
“ME!” button) calls the set of assignable channel
controls to the channel to which that fader is related.
The second modification concerns the assigned
controls. Like the knobless fader, they have to be sepa-
rately acting for indicating. On being called, the indi-
cating part of the control adopts the settings pertinent to
that channel; the control, whether it be knob, switch, or
fader style, can then act on the selected channel with the
indicators following their action on the remote circuitry.Figure 25-117. Quadrature streams from resolver indicating
how speed and directions are sensed.
Figure 25-118. Resolver decoder (using a D-type flip- flop).
Left to right
Signal is checked
on each positive
going transition
of signal B.
Left to right, highAAB+VE
transitionsBAB
+VE
transitionsRight to left
Signal is checked
on +VE transitions
of signal B.
Right to left, low+VE10 k (^7) 10 k 7
A stream
B stream
High one direction.
Low the other
Clock rate
(speed of rotation)
D S Q
C QR
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