Manley BACKBONE Mastering Insert Switcher 2003 - present - Manual (Page 7)

Generally the INPUT and OUTPUT LEVELS are meant to correct for any losses or unintentional
gains from the source machines or in any of the outboard processing gear. However, these controls
really open a lot of possibilities in terms of driving gear hotter or softer especially when one considers
combining that concept with setting up outboard gain settings away from a standard unity gain setting.
The issue here is “the sweet spot” or “gain staging” and the fortunate or unfortunate aspect of many de-
vices that just seem to sound best when driven a little harder or softer than the designer intended. One
can think of it a bit like a guitar amp with its input pot and master volume to get the right amount of
distortion at a comfortable stage volume. Or, one might be more familiar with analog mixing consoles
and liken it to finding that magic combination of individual fader levels and mix-bus fader level.
***In some cases, for “absolute purist fanatics”, even these buffers can be bypassed/removed
(by removing the chips and inserting small jumper wires between pins 3 and 8 on the dip socket)
for one less gain stage in the path – BUT in general they serve a number of beneficial purposes
(including isolating the cable and destination electronics from the gain stage’s feedback loop)
whereas buffer-ectomy may have more of an imaginary benefit . If you can’t hear any change of
quality bypassing ALL the electronics in the console (and so far that is the unanimous opinion),
then don’t even think of possible mods and variations (especially a mod that might be a detriment
in practice). Keep in mind, it also isn’t the kind of change that can be truly A-B compared…***
INSERTS 1-3…SUM-DIFFERENCE PROCESSING
OK, back to the idiosyncrasies of this Insert Box. Next in the signal path is INSERT #1. Pushing
the button marked INSERT 1 engages whatever box might be connected there. When the button is NOT
pushed and lit the main audio path is hard-wire bypassed, of course. However, a little isolation ampli-
fier is engaged to feed that box. This is to pre-drive a compressor so that it is already doing appropriate
gain reduction at the moment that you do insert it. This prevents momentary level changes.
INSERT 2 and INSERT 3 are special. Below these button is another button labeled SUM-DIF
which engages a complete set of Sum / Difference encoders and decoders (or is it the other way
around?). Some people refer to this as M-S (or Mid-Side) but there are also those who insist that these
terms are reserved for mic techniques.
These circuits allow Insert 2 and 3 to act on both the mono (sum) and the side (difference) parts of
the original stereo signal. The left side becomes sum and the right side becomes the difference. So if
you just want to narrow the width of the extreme lows to help cut a lacquer, just cut lows on what was
the right channel of your outboard EQ and is now the “Difference Channel”. After passing through
Insert 2 and 3 the signals are decoded back to left and right. If the SUM-DIF button is not in, Insert 2 &
3 just operate as the other inserts do, as normal stereo left and right.
There is also a 24 position switch that adjusts the level of the difference signal over a -5.5 dB (more
mono) to +6.0 dB (wider) range. This switch is located BEFORE Insert 2 in the signal path, so it will
affect the signal sent to Inserts 2 and 3 if SUM-DIF mode is engaged. Alternatively, one can mix the
difference signal either treated or untreated into the stereo mix near the end of the chain (more on that
later). In other words, you should have more than enough options to mangle the stereo image especially
if you also have yet more sum-diff tools in your digital arsenal. Using it as a cheap trick to impress a
client may have less desirable consequences later. Just beware of mono compatibility and FM radio
transmission issues, difficulties in cutting vinyl records, diminished lead vocals, bass and drums in the
mix (which might be more important to record sales) and reverb balances.
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