This week, the Recording Academy / GRAMMYs announced that Alan Blumlein will be honored with a Technical Grammy in 2017. One of the most significant audio inventors of his time, Blumlein received 128 patents—the most noteworthy was for the stereo in 1931. In his honor, we show you how to capture guitar and vocals using the Blumlein miking technique.
|Sam Stauff records his acoustic guitar and vocal for the latest Wess Meets West release. Two Audio-Technica AT 4050 microphones are set to figureeight,
placed head to head and crossed at 90 degrees.
Way back in the June 2013 issue of Electronic Musician, we examined a variety of
stereo microphone techniques, one of which was Blumlein stereo. This technique
employs two matching figure-eight microphones arranged as a coincident pair—
meaning that they are placed as closely together as possible, with their diaphragms
crossed at an angle of 90 degrees. As shownin Figure 1, neither microphone is
“on axis” to the sound source; they are both 45 degrees off-axis, but since their patterns
overlap in the middle, we still get a strong center image. Blumlein technique
provides a realistic soundstage, with the amount of room ambience dictated by
the distance between the microphones and the source. Somewhere along the way,
engineers adapted Blumlein stereo to solve a very persistent issue typically encountered
when recording a person who is singing and playing the acoustic guitar
at the same time.
SOLVING THE BALANCE PROBLEM
Let’s suppose we’re recording a musician who
is playing the acoustic guitar and singing at the
same time. We’d probably place one microphone
on the guitar, use another for the vocal, and record
each mic to a separate track. Later we could
balance the two tracks in a finished mix, perhaps
adding delay or reverb to one track or the other.
There are problems with this arrangement, mostly
due to the physical proximity of the singer’s
mouth and the guitar. First, even with cardioid or
hypercardioid microphones, it’s very difficult to
control leakage. There will often be a fair amount
of acoustic guitar in the vocal mic and vice versa.
This means that when you mix, it will be tough
to make the vocal louder or add an effect to it
without influencing the sound of the guitar. For
example, if you add delay to the vocal mic, you may hear delay on the guitar as well. If you raise
the level of the guitar track, you’ll probably hear
the vocal get louder too.
The other issue we encounter is phase cancellation.
If we place a mic at the vocalist’s mouth
and a second microphone in front of the guitar,
the mics are separated by roughly one to three
feet. This distance creates a time delay of 1 to 3
milliseconds between the mics, resulting in a perfect
storm that yields a flange when the second
mic is mixed with the first. It usually sounds awful,
but we can literally twist the Blumein technique
into a solution.
|Fig. 1. Diagram of Blumlein configuration. Note that the two microphones are 45 degrees
off-axis to the source, but since the patterns overlap in the middle, we still get a strong
Take a look at our opening image, which shows
artist Sam Stauff recording his vocal and acoustic
guitar for “I Will Break You” from the next Wess
Meets West release. The mic placement is an adaptation
of the Blumlein pair: The front of the
vocal microphone is aimed toward Sam’s mouth,
and the front of the guitar microphone is aimed
toward the area of the guitar were the neck meets
the body. So far this configuration isn’t much different
from using typical cardioid pattern mics.
However the Blumlein configuration enables us
to exploit the figure-eight pattern and reduce leakage
to low levels that can’t be achieved when using
other pickup patterns. The guitar is sitting in the
“null” of the vocal mic’s figure-eight pattern, and
is rejected from that mic. If we make level or EQ
changes to the vocal mic, the guitar is minimally
affected. On the flip side, the guitar mic is placed
so that its null point is facing the vocal—rejecting
it. This isolation provides us with far more control
over each sound when mixing.
One of the most important benefits of this technique
is that it takes advantage the fact that coincident
microphones yield little (if any) phase
cancellation. The diaphragms of the mics in a
coincident pair are very close together (almost
in the same physical location), so sounds arriving
from any direction reach both microphones
essentially at the same time. Why do you care?
Because time delay between two microphones
capturing the same sound produces phase cancellation—
and phase cancellation results in timbral
changes or a flange-type of sound. When we use
the Blumlein arrangement, even if there is some
guitar leaking into the vocal mic, mixing the two
mics (or tracks) together will not cause phase
|Fig. 2. A close-up of Stauff singing, miked with an adapted Blumlein technique.
The amount of leakage at the null of a figure-eight
mic depends upon the integrity of the microphone’s
figure-eight pattern, and will vary
with brand and model. Mics possessing a more
symmetrical figure-eight pattern provide greater
rejection on the sides (at 90 and 270 degrees off-axis).
If there is leakage, then yes, raising the vocal
track might make the guitar a bit
louder, but it’s less of a problem because
it’s not destructive. Note that
the Audio-Technica AT4050 mics
used on Sam for the Wess Meets
West session are set to figure-eight,
and are side-address (see Figure 2).
(Meaning that the side is really the
front. Got that?)
Since you’ve been paying close attention,
you’re now saying, “Ah, but
what about sound hitting the back
of the microphones?” It is true that
the figure-eight pattern captures as
much from the back as it does from
the front, but it’s not really a problem.
The rear of the vocal mic is
pointing toward the floor but is not
capturing much, because this mic is
close to the performer’s mouth and
the mic preamp gain is adjusted for
the vocal, not the relatively quiet reflections
bouncing off the floor. Also,
we’re going to make sure the floor is
The rear of the guitar mic is aimed
at the ceiling. Preamp gain for this
mic is optimized for sound hitting
the front of the mic (the guitar), not
what is bouncing off the ceiling (relatively
low-level reflected sound).
If possible, record in a room with
a relatively high ceiling and/or one
that has absorptive properies. The
results sound very natural and allow
quite a bit of control when it comes
time to mix. You and your artist will
be very happy.
Steve La Cerra is an
independent audio engineer
based in NY. In addition to
being an Electronic Musician
contributor, he mixes front-of-house
for Blue Öyster Cult and
teaches audio at Mercy College
Dobbs Ferry campus.