The=20
theory and practice behind this stereo miking=20
technique
By Phil =
O'Keefe=20
Stereo mic techniques are great for =
capturing and=20
creating a natural, or even a hyper-natural sense of width and space. =
Probably=20
the two most common techniques are the XY coincident arrangement, and a =
spaced=20
pair. But the lesser-known Mid-Side (=E2=80=9CM-S=E2=80=9D) mic =
technique has its advantages too=20
. . . let=E2=80=99s investigate.
THEORY
A lot of people are hesitant to try M-S =
recording, maybe because they read about decoders and math formulas and =
feel=20
overwhelmed. Don=E2=80=99t worry =E2=80=94 we=E2=80=99ll keep it =
simple.
You=E2=80=99ll need two mics: One =
cardioid, and one=20
bi-directional (=E2=80=9Cfigure 8=E2=80=9D). Ideally you want two =
similar mics, but this isn't=20
essential; experiment with whatever mics you have that meet the polar =
pattern=20
requirements.
M-S uses the center or =
=E2=80=9Cmid=E2=80=9D mic in combination=20
with the bi-directional mic to achieve stereo. As the cardioid mic =
points right=20
at the sound source, it picks up the direct sound, while the off-axis=20
bi-directional mic picks up the room ambience and reflected sound. M-S =
stereo=20
=E2=80=9Csum and difference=E2=80=9D is just the center mic + the side =
mic for one channel, and=20
center mic - the side mic for the second stereo channel, with the center =
mic=20
being positive polarity and common to both sides. As the left and right =
sides=20
originate from the same mic, but with the phase inverted, collapsing an =
M-S=20
recording to mono cancels out the left and right sides from the =
bi-directional=20
mic, leaving only the positive polarity signal from the center =
(cardioid)=20
microphone. This significant advantage of M-S recordings insures perfect =
mono=20
compatibility without any phase issues.
SETTING UP THE=20
MICS
Aim the cardioid mic directly at the =
sound=20
source. As with normal cardioid mic placement, adjust the =
=E2=80=9Caim=E2=80=9D to taste; but if=20
you're a fan of close miking, try moving back a bit further from the =
source for=20
M-S recordings.
Next, place the figure-8 mic so that =
the two=20
lobes of the pattern are set 90=C2=B0 relative to the cardioid =
microphone. M-S is a=20
coincident microphone technique, so you want to get the diaphragms of =
the two=20
mics as close together as you can. Fig. 1 shows a =
Soundelux=20
(also known as "Bock Audio") E250 (bottom) and ELUX 251 (top) set up as =
a M-S=20
pair. The cardioid E250 is pointed at the sound source (in this case, =
the=20
camera), while the pattern selector on the ELUX is set to =
bi-directional; it=E2=80=99s=20
picking up to the left and right, and its side null point points =
directly at the=20
sound source/camera.
Fig. 1: A=20
Soundelux E250 (bottom) and ELUX 251 (top) set up as a M-S=20
pair
SETTING UP THE BOARD AND=20
RECORDING
At your DAW, simply route each mic to =
its own=20
preamp, and assign the cardioid mic to a single DAW track. You can =
either record=20
the bi-directional mic to two identical, separate tracks of its own and =
invert=20
the polarity of one of the two tracks later, or record the =
bi-directional mic to=20
only one track and use a decoder plug-in, or clone the single =
bi-directional=20
mic's track later and invert the clone track=E2=80=99s polarity =
=E2=80=94 your choice. I=20
generally record the bi-directional mic to two tracks simultaneously in =
Pro=20
Tools, labeled =E2=80=9CSIDE+=E2=80=9D and =E2=80=9CSIDE-,=E2=80=9D and =
insert a Trim plug-in on the =E2=80=9CSIDE-=E2=80=9D=20
track to invert the phase. Fig. 2 shows a basic M-S =
track=20
arrangement in Pro Tools.
Now group the two =
=E2=80=9CSIDE=E2=80=9D tracks so that any=20
changes you make to the volume level of one will apply to the other =
track=20
simultaneously, and pan the tracks hard left and right. As you raise the =
level=20
of the side mic tracks, the stereo width will increase; lowering them =
decreases=20
it. Being able to adjust the amount of stereo information in the =
recording after=20
the fact is one of the big advantages of M-S recordings.
Fig. 2: A basic=20
Mid-Side track and panning arrangement in Pro Tools. Note the use of the =
Trim=20
plugin to reverse the polarity (red arrow) on the "Side -" cloned =
track=20
FREE=20
DECODER RING INSIDE!
So why would you need a decoder or =
hardware=20
matrix box? The downside of simply cloning the =E2=80=9Cside=E2=80=9D =
mic track and inverting=20
the polarity is that you can=E2=80=99t hear the final results as you =
position the mics =E2=80=94=20
you have to record them, then flip the polarity and start playback. By =
encoding=20
the sum and difference data from the two mics and recording the result, =
you can=20
hear how the stereo field will sound before you track. PAiA has a =
hardware M-S=20
matrix box schematic available on their website for you solder jockeys: =
http://www.paia.com/ProdArticles/msdecwork.htm. =
For=20
other DAW users, Voxengo=E2=80=99s free MSED M-S decoder plug-in (Mac =
AU/VST, Win VST)=20
works very well; download it from http://www.voxengo.com/downloads/.
M-S might not be used as frequently as =
some other=20
stereo techniques, but the perfect mono compatibility and ability to =
adjust the=20
stereo width at mixdown make it handy for broadcast production, live =
recordings=20
of small ensembles, individual instruments, and small groups of =
background=20
vocalists on multitrack music sessions. Give it a try!
Phil O'Keefe is a multi-instrumentalist, recording engineer =
/=20
producer and the Associate Editor of Harmony Central. He has engineered, =
produced and performed on countless recording sessions in a diverse =
range of=20
styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow =
Skulls, John=20
McGill, Michael Knott and Alexa's Wish. He is a former featured monthly=20
columnist for EQ magazine, and his articles and product reviews have =
also=20
appeared in Keyboard, Electronic Musician and Guitar Player magazines.=20