Stereo Microphone Techniques
If you are a musician or music producer, you may have a lot of complaints about the bad sound quality of many productions out there. In many cases, it is due to a bad stereo microphone technique, which is, by the way, one of the most powerful tools at our disposal for creating a rich, detailed sound in a recording.
In this post, we’re going to explore some of the most popular stereo-miking techniques and how they can be used to create an incredibly detailed and spatial sound mix. If you’re just starting on this path, this post will be quite helpful for you. If you’re already a connoisseur, maybe you can learn a thing or two.
Okay, first let’s talk about what stereo recording is. In case you don’t know it yet, it’s a technique that uses two microphones at the same time to record the same instrument. Then, the mono signal from each of the microphones is assigned to the left and right channels of a stereo track to create a sense of spaciousness in the recording.
The stereo effect is thus created by the slight difference between the left and right channels of the studio monitors, which is observed in two ways. First, the time difference: by placing the microphones in different locations, the sound of the instrument arrives at each microphone with a slight time difference. That difference (of only a few milliseconds) is enough to create the stereo effect. Second, there is a difference in frequency balance because, by angling the microphones in different directions towards the instrument, each microphone picks up a slightly different frequency balance. The more open the angle, the greater the stereo effect.
So, when one mic is heard on the left monitor and the other on the right, it creates a nice amplitude effect that does not exist in mono recordings.
Let’s look at the most commonly used techniques.
A/B technique (separate pair)
This uses two small diaphragm omnidirectional condenser microphones placed about 11,8 inches from the instrument, 23,6 inches apart. The mix is assigned to the left and right channels to create a stereo image, but temporary decompensation between the microphones can cause phase cancellation problems when converting the stereo signal to mono. Experimenting with the distance between the microphones and the instrument can affect the result. This technique is commonly used for recording acoustic instruments and vocals in a studio setting.
X/Y technique (matched pair)
This one uses two small-diaphragm directional condenser microphones, which are positioned at an angle of between 90–135 degrees so that the capsules are matched by only one point, creating a less pronounced stereo image than the A/B technique. The mix is assigned to the left and right channels, just as in the A/B technique, but the lack of time difference in signal arrival means that the stereo effect is created by the difference in frequency balance, which eliminates the problems of phase cancellation in mono. The X/Y technique is commonly used in the recording of string and wind instruments.
ORTF technique
This one is quite popular. Here, the pair of microphones (yes, also small-diaphragm condenser directional…) is placed at an angle of about 110 degrees with a distance of about 6,6 inches between each capsule. As in the A/B technique, the mix is assigned to the left and right channels. This technique is a combination of the A/B and X/Y techniques, which produces a wider stereo image due to the separation of the microphones and picks up less ambient sound by using directional microphones. It is commonly used in the recording of percussion instruments and natural environments.
Blumlein Technique
If you don’t like the previous one, try this one. The Blumlein stereo miking technique uses two bidirectional microphones, positioned as in the X/Y technique. Mixing is done in a similar way to the X/Y technique. This one provides a more natural and spatial stereo image than the X/Y technique because the bidirectional microphones pick up more ambient sound. Furthermore, this technique provides a good sense of depth and a detailed stereo image. It is particularly suitable for recording acoustic instruments and vocals in the studio, as it can faithfully reproduce the acoustic interaction of the environment in which the instrument or voice is located.
M/S (middle/side) technique
Finally, we have the M/S technique, which uses two diaphragm condenser microphones, one must be bidirectional while the other can be cardioid or omnidirectional. The bidirectional microphone is placed sideways at a 90-degree angle to the other microphone, and records in both directions, performing the “side” function in the “middle/side”. The other microphone is placed above or below the bidirectional microphone and points directly toward the instrument, performing the “middle” function. M/S is key for detailed sound recording and accurate stereo imaging, capturing both the ambiance and the direct sound of the instrument.
Remember that if you need help or advice on recording, don’t hesitate to contact Enhanced Media Sound Studio, where our audio experts can help you get the best possible sound quality for your audiovisual projects.
