The six microphone techniques I'll show you in this video can be used in so many different ways,
from getting a huge drum sound for a rock album to giving a listener the opportunity to virtually sit
inside of a beautiful concert hall without ever leaving the comfort of their own home.
This week I'm working with Ernesto Doural Jr. on drums and recording engineer and producer
Rich Harris at Shock City Studios in St. Louis.
If you're new to this, channel my name is Kyle. Welcome to Audio University.
Not only are the techniques useful, but the concepts behind the techniques are absolutely
essential if you want to learn to create more immersive audio experiences for music, film,
or video games. The most important thing I want you to take away from this video is that there are
a few ways humans determine the direction a sound is coming from, called sound localization cues. As
recording engineers, we can use these principles to create a spatial element in our recordings.
The first localization cue is called an interaural level difference, or an ILD. An interaural level
difference basically describes the difference in level between the left ear and the right ear.
Imagine a snare drum placed directly in front of you. The sound from the snare drum travels the
same distance to both your left ear and your right ear and is therefore equally loud in both ears.
This tells your brain that the snare drum is directly in front of you.
However, if the snare drum were placed off to your right side, the sound would take a longer
path to your left ear and would be slightly quieter by the time it reached the left ear.
This would indicate to your brain that the sound originated on your right side.
The second sound localization queue is called an interaural timing difference, or an ITD. An ITD
describes the difference in the time of arrival between the left ear and the right ear.
Going back to the snare drum example, not only would the sound be quieter in the left ear if
the drum were placed off to the right side, but it would also reach the right ear sooner than it
would reach the left ear. If the brain detects a sound in the right ear before detecting the
sound in the left ear, it will determine that sound to have originated from the right side.
The last sound localization cue I want to talk about is called a head-related transfer function.
In basic terms, a transfer function is just the effect a component of a system has on a signal
passing through that system. In this case, we're describing the effect that the listener's head
has on sounds reaching each ear. If I talk directly into this microphone,
it sounds a lot different than if I placed my hand in front of the microphone.
This case is describing a hand-related transfer function. The listener's head could have a similar
effect. A sound originating on the right side might sound a little bit darker in the left
ear than the right. By the time the sound gets around the skull, the shadowing of the skull
might cause a little bit of high frequency loss by the time it reaches the left ear.
Now let's talk about how these localization cues can be harnessed by recording engineers to make
more immersive recordings. I'll walk through the four general types of stereo microphone techniques
going through the pros and cons of each of them. I'm also going to show you six
techniques that you can try for yourself. To learn even more techniques, check out the full post at
audiouniversityonline.com/stereo-microphone-techniques/.
The first type I want to show you is called a coincident pair.
The word coincident indicates that the two microphones occupy the same point in space. Now,
the benefit of a coincident pair is that the two microphones are aligned in space
and therefore they're aligned in time, so if you were to sum the left and right channel
together to mono there wouldn't be any phase interference. This is called mono compatibility.
The first technique I want to show you is called X-Y.
To set up a pair of microphones in X-Y, you simply place two directional microphones with
the diaphragms aligned at a 90-degree angle. Pan the right-facing microphone to the right and pan
the left-facing microphone to the left. This technique operates on the principle of an ILD,
or interaural level difference. Because these are cardioid microphones,
sounds on the right side will be louder in the right-facing microphone, because they'll be
on-axis with the right-facing mic while being 90-degrees off-axis with the left-facing mic.
The second technique is very similar to the X-Y technique, but it utilizes a pair
of bi-directional or figure 8 microphones instead of cardioid mics. This method is called Blumlein.
You simply place two microphones with their polar patterns perpendicular to one another.
Again, you'll pan the right-facing microphone to the right and pan the
left-facing microphone to the left. Depending on the style of microphone you're using,
you might need to turn one microphone upside down to get the right placement.
The third technique I want to show you is also a coincident pair, called Mid-Side.
This technique is a bit more complicated to set up, but bear with me because it's definitely worth
it. One microphone in this setup has a cardioid polar pattern and it's facing directly ahead.
The other microphone has a bi-directional, or figure-eight, polar pattern and faces
perpendicular to the cardioid mic. The two microphones come into your mixer or DAW. Once they
get there, you'll duplicate the bidirectional mic and invert the polarity on one copy.
Now you've got three channels - a front-facing cardioid (called the mid microphone) and two
copies of the side microphone that are in opposite polarity. Leave the mid microphone panned to the
center and pan one copy of the side microphone all the way to the left and the other copy all the way
to the right. This setup allows you to adjust the stereo width of your recording after you record.
Turning the side microphones up will make the stereo width wider, while turning the side
microphones down will keep the sound anchored in the center. The best part about the Mid-Side
technique is that it's 100% mono-compatible. When the three channels are mixed together into mono,
the left and right side signals simply cancel out, leaving only the mid channel.
The second type of technique I want to show you is called a near-coincident pair.
In a near-coincident pair, the two microphones are close to the same position but not quite. Now,
of course, this means that when they're summed to mono there will be some phase interference,
but it also means that we can now catch ITDs, or interaural timing differences. Sounds originating
from the right side will reach the right microphone before reaching the left microphone,
which could send a signal to the listener's brain that the sound must be coming from the right side.
One of the most popular near-coincident microphone techniques is called ORTF.
To set up a pair of microphones in ORTF, place two directional mics about 17 centimeters apart
facing 110-degrees away from each other. Pan the right-facing mic to the right and the left-facing
mic to the left. This method harnesses the power of both interaural level differences
and interaural timing differences. A sound originating from the right side will be both
on-axis with the right-facing microphone and will reach the right-facing microphone first.
Next let's take a look at the type of stereo microphone technique called a spaced pair. In
a spaced pair, there's much more distance between the microphones than in a near-coincident pair.
One example of a spaced pair technique is a spaced omni. This is simply a pair
of omnidirectional microphones placed anywhere from a few feet apart to several meters apart.
One drawback of this technique is that you really need to dial in the placement before
pressing record. Placing them too close together might give you too narrow of a stereo image,
while placing them too far apart may give you a hole in the middle of your stereo image.
The last type of stereo microphone technique I want to show you is called a baffled pair. Now,
a baffled pair could technically be considered a near-coincident pair, but with a twist. With
a baffled pair, we're going to actually place a barrier between the two microphones and this gives
us a big advantage, because now we can capitalize on all three of the localization cues - interaural
level differences, interaural timing differences, and head-related transfer function.
Several companies produce microphones specifically designed for making binaural recordings.
These microphones aren't cheap, but they offer extremely realistic sound
by using two microphones placed in an artificial human head.
You can get a similar effect by using two omnidirectional lav microphones. I'll place
these microphones just inside my ears and use my skull as the baffle between the two mics.
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