Audio-Technica AT4050ST
A side-address stereo condenser that hands you a finished left-right pair — or the raw mid-side signals, if you'd rather do the matrixing yourself.
Overview
The AT4050ST is one of those microphones that solves a problem you didn't know you had until you tried to record a choir, a drum kit, or a string section with two separate mics and spent an hour aligning them. It's a stereo side-address externally polarized (dc bias) condenser built around two independent elements — a cardioid capsule and a figure-of-eight capsule — arranged in a mid-side configuration. That arrangement is the whole point of the thing, and it's what separates it from the rest of Audio-Technica's 40 Series.
What makes the AT4050ST unusual is that it gives the engineer a choice at the microphone itself. Switch-selectable internal matrixing converts the mid-side pair into a conventional left-right stereo output, and the mic offers two widths for that matrixed signal — a wide 127-degree spread or a narrower 90-degree spread. Flip the switch the other way and the AT4050ST outputs discrete mid and side signals, leaving the matrixing to a console, a DAW plugin, or a outboard box. That's a genuinely useful bit of flexibility: capture once in mid-side, and you can adjust the stereo image in post rather than committing to a width at the session.
The design was, according to Audio-Technica's own materials, developed in direct response to feedback from end users — which is the kind of line that usually means nothing, but here it tracks with the feature set. Mid-side recording has long been a favorite of engineers who want mono compatibility and adjustable width, and a single-body stereo condenser that does the matrixing internally is a convenience item for anyone recording location sound, ensembles, or drum overheads without a matched pair of mics and a stand bar.
Audio-Technica positioned the AT4050ST as part of its flagship 40 Series, and when the company added four new microphones to that line around 2010, the AT4050ST was announced alongside the AT4080 and AT4081 ribbon mics and the AT4047MP multi-pattern condenser. Mix (2010, p.11) ran the launch copy describing the AT4050ST as offering "Mid-Side stereo realism" and noted that each microphone in the group was backed with a 5-year warranty — a detail worth remembering if you're buying used, since the original coverage won't transfer but it says something about how the company regarded the build.
The AT4050ST also turns up repeatedly in Audio-Technica's promotional material across the early-to-mid 2010s. Mix (2010, p.3) pictured it in a 40 Series lineup under the heading "Stereo Condenser Microphone," and the mic was included in the company's recurring rebate promotions — buy a select 40 Series mic, get a free pair of ATH-M50 or later ATH-M50x headphones. Pro Sound (October 2015, p.4) ran the ATH-M50x rebate offer listing the AT4050ST among the qualifying 40 Series models, and Mix (2013, p.87) ran a similar M50 promotion with the AT4050ST featured prominently. None of that tells you how the mic sounds, but it does confirm the AT4050ST stayed in the active 40 Series catalog for years rather than being a one-off.
As for how it actually behaves in a room: the AT4050ST is a side-address design, meaning you point the grille at the source and speak into the side of the body rather than the end. That's standard for large-diaphragm condensers and makes it easy to position in a shock mount or on a stand in front of an ensemble. The two-element mid-side arrangement is what does the stereo work, and the internal matrixing means you don't need a second mic, a stand bar, or a console with M-S decoding to get a stereo capture — though the option to bypass the matrixing and record discrete mid and side is there for anyone who wants it.
One thing to be clear about: the AT4050ST is a stereo microphone, not a multi-pattern mono mic. The cardioid and figure-of-eight elements are fixed in their roles and configured in mid-side; the switching is about how those two signals are combined or output, not about selecting polar patterns the way you would on a multi-pattern condenser. If you need a single-cardioid workhorse, that's a different tool. If you need a stereo pair in one body with adjustable width and the option to re-matrix in post, the AT4050ST is built for exactly that job.
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