Mostly everyone of us has two ears, left and right. In the middle between them, most of us got our head… Well, if you don’t have a head between your ears, you might be in trouble… so, why am I writing this? what does it have to do with stereo recording techniques? Well, just everything.
When we perform a stereo recording, somehow, we are using microphones to imitate left and right ears with a head just in the middle. So, positioning two mics one next to the other, both facing front, it is not a stereo recording technique, but, positioning them with their capsules facing each other forming a 90 degrees angles, it is, and that’s called X/Y technique.
In the picture we can see two cardiod small diaphragm mics placed in X/Y so, right mic is capturing what’s in the middle and to the left of the stereo image and left is capturing what’s in the middle and to the right of the image. This technique, has a really big pro and one con. Pro: no phase issues! so, when you play it Mono, you will have no phase problems. Con: the stereo image is not as wide as with other techniques.
On the other hand we’ve got A/B or wide stereo technique. As it name suggests, it produces a wider stereo image than X/Y technique.
As we can see in the image, we have two cardiod small diaphragm condenser mics both facing front and with a separation of 50 to 60 cms. Somehow, this imitates how our ears work. Two matched ears= two matched mics; a head between ears= 50 to 60 cms separation between mics.
This technique has an obvious pro, and that’s a wide stereo image, much wider than X/Y. In the other hand, you can have many phase issues using this technique and you may experience big problems when reproducing in Mono.
Maybe the oldest and more intriguing stereo recording technique is M/S or Mid-Side invented by Alan Blumlein. Belive it or not, this is the oldest recording technique.
As we can see in the image, we’ve got two microphones one on top of the other. One of the mics should have a cardiod or omnidirectional polar pattern, and must be facing the sound source, the other mic, must be a figure of 8 or bidirectional, and must be capturing the sides, so, one facing front and the other facing sides. you will need to duplicate the figure of 8 mic track and invert it’s phase (as explained in the figure below), and that’s it, stereo image in three tracks. Cardiod/omni mic giving you the Mid and bidirectional mic giving you the sides! Another way to get M/S is to use an M/S decoder plugin, so you don’t have to duplicate the S track and invert it’s phase.
Another technique is ORTF (Office de Radiodiffusion Télévision Française). And is quite similar to A/B technique.
As we can see in the picture, it also consist of two cardiod mics, but in an angle of 110 degrees and with a separation of 17 cms. This technique provides a really nice stereo image and has very few phase issues when played Mono.
Alan Blumlein did not only invented the M/S technique, he also invented another technique that still is named after him Blumlein pair, which consist, as we can see in the picture, of two bidirectional mics positioned 90 degrees from each other. It’s like X/Y technique, but using two bidirectional (8 figure) mics. It picks up a very interesting stereo image and room ambience. Unlike M/S technique, you won’t need decoding or inverting phases. In general, you won’t experience any phase issues with this technique, and personally I think it’s great to capture ambience in recording electric guitars, pianos or drums.
Below, you can listen to our comparison. A little piano pice recorded with all this techniques, all at the same distance (about 1.5 mts from source). No processing or effects applied.