This Is Stereo! PART 6

With an understanding of spaced and coincident stereo arrays, we can exploit the characteristics of both — using either established arrays, or by creating our own!

In previous parts of this series, we’ve explored the concepts of coincident and spaced stereo mic arrays. I hope you’ll recall that while coincident arrays generally deliver stable and precise stereo imaging, they’re often described as lacking ‘spaciousness’; in contrast, spaced arrays excel in the ‘spaciousness’ department but their stereo imaging is typically vague and unstable.

There’s no technical reason, though, why these disparate approaches can’t be combined to create a ‘hybrid’ array — one which uses directional polar patterns set with a mutual angle, but with the mics spaced apart. Indeed such stereo mic arrays are common and popular, and it’s probably fair to say that most recording engineers use them most of the time! As with all the other stereo arrays we’ve considered, there are no fixed rules; the recording engineer can employ any capsule spacing, polar pattern and mutual angle they think appropriate for any given situation, bearing in mind that these parameters interact to determine the Stereo Recording Angle (SRA) of the array, as well as the overall character of sound.

As with coincident mic array setups (crossed cardioids, Blumlein, Mid‑Sides and so forth), there are many precisely defined and named hybrid mic arrays, most being devised by European broadcasters in the early 1960s and consequently named after those organisations.

Popular Hybrid Stereo Arrays

The best known and most popular is the ORTF mic technique, which was developed around 1964 by the Office de Radiodiffusion Télévision Française (the post‑war French state broadcaster, which was broken up into seven new broadcasting companies in 1974, including TF1, TF2, FR3, and Radio France). For this array, two cardioid capsules are spaced apart by 170mm, and face outwards with a 110‑degree mutual angle to give an SRA of 96 degrees. At around the same time, in the Netherlands, the national broadcasting foundation (Nederlandse Omroep Stichting) came up with a variation on the same theme. This NOS configuration also uses cardioid capsules but they’re arranged with a 90‑degree mutual angle and a 300mm capsule spacing, a combination that gives a slightly narrower SRA of 81 degrees. And in Germany, the Deutsches Institut für Normung standards institute came up with the DIN array. This also employs cardioids with a mutual angle of 90 degrees, but its slightly narrower capsule spacing of 200mm gives a wider SRA of 102 degrees.

There are virtually limitless combinations of different capsule spacings, mutual angles and polar patterns, so not surprisingly there are other less well‑known named formats, such as RAI (cardioids, 210mm spacing, 100‑degree mutual angle) and EBS (cardioids, 250mm spacing, 90‑degree angle). I’ve skipped over these simply because they’re so similar to the arrays I’ve already described, but I will highlight one more option, since I plan on returning to it in the context of post‑production signal processing in a later article. The Gerzon array employs cardioid capsules with a mutual angle of 120 degrees and a spacing of just 50mm, giving an SRA of 130 degrees. This array was named after and promoted in the 1980s by Michael Gerzon, a genius who’s probably best known as the inventor of (first‑order) Ambisonics and the SoundField microphone, and who credited the array to award‑winning recording engineer and producer, Tony Faulkner....