Audio Developments AD149 - Manual (Page 55)

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have to apply an HPF to the S-signal only, in order to reduce low-frequency content
(with respect to the M-signal).
Still within the 'Blumlein Loop' is the input-balance control BAL (23). For maximum
flexibility, this control is zero-to-zero, ie when fully anti-clockwise, only the left-hand
signal is available and when fully clockwise, only the right-hand signal is available.
This control changes the width of a stereo signal from mono to enhanced stereo
(through to a meaningless S-signal). BAL (23) can be used to re-balance an input
signal that is in the L-R domain, although this can also be done using the
STEER control (24), which has finer resolution because of its restricted range.
Insert points - within the 'Blumlein Loop' - permit the addition of external processors or
floating equalisers from mono modules, or the differential application of FLEX-EQ for
shuffling. Matrix 2 closes the 'Blumlein Loop'.
If (during post-production) the input signal is in the L-R domain, matrix 1 will convert
the signal to the M-S domain for Blumlein processing, before being returned to the
L-R domain by matrix 2. If the input signal is already in the M-S domain, only matrix
2 will be used - to return the signal to the L-R domain.
Now (that) the stereo signal is in the L-R domain, it can be meaningfully mixed, pre
and post the stereo fader, for routeing to auxiliary 1 (8) and auxiliary 2 (10). Each
auxiliary path has its own ON switch - (7) and (9). Overriding the source selectors
(8) and (10) is the auxiliary stereo link - ST (11) - which routes a stereo form of the
module input to auxiliaries 1 and 2. ST (11) also converts auxiliary 2 level control into
the stereo level-control to the auxiliary mix busses.
In order to be consistent during post-production with the mono line module, no extra
gain is available when auxiliaries are sourced pre fader.
When designing this module, very careful consideration was given to the following
points: where to select the L-input only, where to select the R-input only, where to mix
the stereo input and the effect any decision would have on the auxiliaries, particularly
when only one half of the stereo signal is to be used; and whether the post-fader mix
point for the auxiliaries should be pre or post the steer control.
We have already seen that by mixing as late as possible (within the channel), different
equalisation may be applied to the left and right signal paths. By mixing after the
STEER control, the effect of steering on a mono mix may be evaluated.
If only the left or the right input is to be processed, it may be selected by BAL
(23). By the same token, the balance control, being calibrated zero-to-zero, enables
any balance of the stereo input-signal to be processed.
STEER (24) is a second balance potentiometer (with reduced range) which steers the
L/R output from the module to its correct place in the final L-R image.