Most of the recording
I do involves tracking several musicians playing together in a room.
I’d like to use a stereo pair to capture the overall picture, as well as
close miking, but often the musicians arrange themselves in such a way
that X-Y or A-B rigs won’t work. I’ve been wondering about using
a Blumlein-crossed figure-of-eight pair placed between the drummer and
the rest of the group, in such a way that the front of the array
captures the drum kit and the rear captures the other musicians. In
other words, is Blumlein strictly restricted to the 90-degree acceptance
angle in front, or is it OK to use the 90-degree space behind the array
too? And if so, should I reverse the polarity of any other mics on that
side?
You
actually have little choice over whether to use the rear of your mics
in a Blumlein array, as the mics will always capture ambient noise to
the rear of the setup. This can be quite useful in certain
circumstances, such as radio drama, for example, in which the setup
allows the actors to be positioned less rigidly but still be picked up
by the mics.
Simon Earle, via email
SOS
Technical Editor Hugh Robjohns replies:
The short answer is yes, it’s
perfectly OK to use the rear pick-up region, and yes, you might need to
reverse the polarity of spot mics covering sources on the rear of the
Blumlein array.
The slightly longer answer is
that you actually have no choice in the matter; the rear side of
a Blumlein array is captured anyway, so you might as well make use of
it. In an orchestral recording, for example, it will be capturing the
room ambience and audience (which will make it sound rather more open
than might be expected). In radio drama, both sides of a Blumlein array
are often used to great effect, as the technique allows the actors to
face each other across the mic for good eye-contact, while still being
able to move freely within their own ‘stereo space’.
In
your situation, it’s perfectly acceptable to arrange the musicians to
use both front and rear 90-degree stereo-recording angles, using
relative distances from the mics to help achieve the appropriate
balance. In radio drama, the studio floor is often marked up with tape
to identify the edges of the 90-degree pickup areas, with additional
marks to show the desired positions for each performer, so they don’t
wander away and upset the optimum balance.
There
are two things to beware of. Firstly, don’t let any real sound sources
move around to the sides of the Blumlein pair, because they will then be
out of phase in the stereo image. Secondly, choose your figure-of-eight
mics carefully, as many are designed with strong tonal differences
between front and back. That may be quite useful in your situation, but
can cause significant issues in others. Finally, if you’re planning to
close-mic sources to supplement their contributions to the main pair
balance, sources on the rear of the mic will be captured with an
inverted polarity relative to those on the front, as you say.
Consequently,
you will probably need to flip the polarity of those close mics in the
mix to avoid phase cancellation issues, depending, to a degree, on the
distance between the close mics and Blumlein pair, the nature of the
source, and the level of the spot-mic contribution. I’d start with the
rear-side close mics flipped in polarity, and check each one as you
build the mix, to see what works best.
No comments:
Post a Comment