In the comfortable confines of a studio, you can position microphones as you please. Want more detail? Just move the mic closer to the source. In the rough-and-tumble world of field recording, however, it's often impossible to position a microphone as close to the source as you'd like. Imagine, for example, trying to record the sound of a squirrel eating a walnut. It would be great if you could position the mic inches from the rodent's maw, but what wild creature is going to allow that?
A common solution for that type of challenge is to record with a shotgun microphone, a key item in the field recordist's handbag. Shotgun mics (also called interference tube or line cardioid microphones) use a highly focused polar pattern — tighter than hypercardioid — to capture distant sounds. They are especially useful in noisy or reverberant environments because of their ability to accurately home in on a particular sound while rejecting surrounding sounds.
Audio-Technica's AT835ST is not only a shotgun microphone but also a stereo mic. Single-point stereo mics (one microphone housing two capsules) are commonly used for field recording and for video- and film-production sound work. Single-point stereo mics usually have better mono compatibility than a spaced pair of microphones, and they also minimize the size and weight of the rig — important concerns in the field. (For more about shotgun mics, see the sidebar “I Said Shotgun.”)
WHERE IT'S AT
The build quality of the AT835ST inspires confidence. A little more than nine inches long, the microphone is made of sturdy yet lightweight metal with a gray-bronze finish and subtle black dapples (see Fig. 1). The connector end provides a balanced stereo output on a 5-pin XLR connector. The electret condenser capsules are near the connector and visible through the slots cut into the tube. (When mounting or holding the mic, don't obstruct that area, or performance will suffer.)
The mic has two switches recessed deep into the body and movable only with a narrow tool. The first provides access to a highpass filter at 80 Hz; the second is a three-position switch that allows control of the stereo image width. The first setting, marked MS, disables the mic's built-in M-S decoder, permitting variable-width processing (see the sidebar “Shotgun Wedding”). The other two positions, LR-W and LR-N, engage the decoding circuitry to create wide or narrow stereo images, respectively.
I rarely used the normal position; during mixdown, you can easily reduce a wide image to a narrower one, or even to mono, by simply panning the signal's left and right halves toward the center. In addition, collapsing the signal to mono won't create phase problems, as often occurs when using other stereo-miking techniques; rather, the side signals cancel out, and you're left with a recording of what the mid capsule alone heard.
The AT835ST comes in a well-padded snap-shut storage box (made of vinyl-covered cardboard), complete with a rigid mic clip, light-duty foam windscreen, and short stereo cable (5-pin female to dual 3-pin male). One small annoyance: the AT835ST's storage box is significantly larger than necessary. (That is because Audio-Technica uses the same box to accommodate its longer stereo shotgun mic, the AT815ST.)
I look at a number of characteristics when judging a mic's suitability for field recording. Sound quality is obviously critical, but there are other important factors to consider, such as electronic self-noise, size and weight, and handling noise. For a stereo mic, stereo-imaging quality is also important.
The AT835ST sounds good. On the provided spec sheet, the mic shows a broad boost in the highs between 2 and 10 kHz with a 4 to 5 dB bump around 7.5 kHz. That extra high end enhances dialog intelligibility and can help clarify distant sounds; however, it can also impart an edgy character to some sources. On the low end, the AT835ST dips about 4 dB at 80 Hz.
The main purpose of a shotgun mic is to accurately capture the target sound while minimizing off-axis noise. To that end, the AT835ST is a target-specific instrument. Note that the Narrow and Wide modes do not have an effect on the directionality of the shotgun capsule; instead, they raise the relative level of the figure-8 side mic. When using the AT835ST in Wide mode, therefore, you hear a fair amount of stereo ambience along with the sound at which you're aiming. Collapse the image to mono after the fact (or record in undecoded M-S mode), though, and you'll be impressed by the amount of rejected ambience and off-axis sound. (If you need even greater directionality, check out the aforementioned AT815ST, a physically longer and more focused version of essentially the same instrument.)
QUIET ON THE SET
Because field recordists may be called on to record very quiet sounds — for example, the murmur of a creek, leaves rustling across a lawn, or a clock ticking in a quiet house — mic self-noise is an important consideration. The mic preamp you use can contribute significantly to noise, so I tested the AT835ST using an outstanding and very quiet mic pre: a Grace Designs Lunatec V2.
The AT835ST uses electret condenser capsules — capsules that tend to be noisier than a true condenser (that is, one with an externally polarized capacitor). The AT835ST performed about as I expected for its reasonable price: it was somewhat noisy. Therefore, it would not be my first pick for recording really quiet sources; for louder applications, however, it is sufficiently quiet.
The first AT835ST I tested suffered from a tiny but noticeable sputtering sound coming from the figure-8 capsule. It turned out that the mic was defective, so Audio-Technica sent a replacement. Thankfully, the second microphone did not exhibit the sputtering noise.
The AT835ST showed typical amounts of handling and infrasonic noise. Also, though adequate on calm days, the slipover foam windscreen that comes with the AT835ST is insufficient in moderate or stiff winds. The solution to both problems is to budget for a combined shockmount and windscreen, such as those manufactured by Rycote (www.rycote.com).
Audio-Technica supplied a top-of-the-line Rycote Windshield and Windjammer. The Windshield comprises a tube made of flexible plastic netting with an adjustable suspension mount inside and a pistol-grip handle. The Windjammer is a faux-fur sock that slips over the Windjammer. I did my outdoor testing using the Windshield and Windjammer combination, and it worked beautifully. Even on the open observation coach of a speeding passenger train, wind noise remained under control. Rycotes aren't cheap, but they do the job well.
SLIM AND TRIM
Size and weight are obvious considerations for microphones meant for use in the field. The AT835ST is relatively compact and very lightweight. It's also comfortable to use for extended periods, either when handheld in a shock-mounted pistol grip or cradled at the end of a boom pole.
Power requirements for condenser mics are another important consideration for the field recordist. The AT835ST requires external phantom power (11 to 52 VDC); internal battery power is not an option. In the past, I have been willing to suffer the higher self-noise of an electret condenser mic because the internal battery provided easy interfacing with ultraportable consumer DAT and MiniDisc (MD) recorders (which rarely provide phantom power). The AT835ST offers no such trade-off. In addition, balanced line transformers are required when connecting the mic to an unbalanced mic input — a potentially cumbersome requirement in the field.
If your field recorder provides XLR mic inputs and phantom power, neither concern is an issue. As Audio-Technica points out, XLR jacks and phantom power have become commonplace on “prosumer” sound and video gear. However, given the AT835ST's competitive price, it will also appeal to many sound recordists using consumer-grade gear. If you're in that group, be aware that interfacing the mic to your rig will not be a trivial task.
Though the AT835ST delivers pleasant ambience, its stereo imaging reflects a compromise inherent to such directional microphones: it images strongly to the center and sides, with somewhat vague transitions in between. In addition, I encountered occasional left-right ambiguity with moving sound sources. That is no surprise, because the microphone is primarily designed with directionality rather than stereo imaging as its main goal.
What it comes down to is choosing the right tool for the job. If your primary goal is to capture realistic stereo environments, for instance, a nonshotgun stereo mic is a better choice. (I have had good success with the less-expensive Audio-Technica AT825 and my primary single-point stereo mic, the slightly pricier Shure VP88.)
AT PLAY IN THE FIELD
I took the AT835ST to New Zealand and returned with some memorable sounds. In a forest at the edge of a coastal marsh on the South Island, I was attempting to capture the sound of a bellbird in a high tree when a large gull-shaped bird flew overhead. Luckily for me, I was recording. The AT835ST captured the sound of the bird grunting with each flap of its wings as it swooped over the forest canopy. The sound would be right at home in the pod-racer sequence from Star Wars, Episode I: The Phantom Menace; it was that weird.
On the barren banks of a glacial lake at the foot of Mount Cook, I came upon a chunk of ice drifting 20 feet offshore. By positioning the mic at the water's edge, I captured the glassy lapping of the windblown lake against the distant melting ice block, all the while keeping my feet warm and dry (see Fig. 2).
Later that afternoon, I encountered a small rocky stream and “fished” for voices in the bubbling water. Although I was working at close range, the AT835ST's directionality was still helpful; it let me target minute areas of the stream's soundscape. As I moved the mic from rock to rock, listening for a good location, inspiration struck. I took the recorder out of pause and, holding the microphone, began a series of slow, sweeping gestures over the stream. My goal was to create a short piece in which the fades and transitions were created live at the microphone rather than by editing and crossfading back in the studio. It worked. A good tool should inspire new ways of working, and the AT835ST came through on that count.
The Audio-Technica AT835ST stereo shotgun microphone strikes a good balance between sound, features, and price. In fact, no other stereo shotgun mic comes even close to the low price of the AT835ST.
I recommend the AT835ST, but with a couple of caveats. The first relates to its self-noise. Although the mic is not loud enough to be a concern if you are recording a soccer match, for example, you may wish it were a bit quieter as you crouch behind a bush, trying to capture a distant birdcall. My other warning is relevant only to users of semipro gear, and that's simply to be aware that you need phantom power and balanced transformers to hook up the AT835ST to a portable DAT or MD recorder.
Rudy Trubitt is a writer and recordist from Oakland, California. His books Mackie Compact Mixers and Live Sound for Musicians are available through his Web site,www.trubitt.com.
stereo shotgun microphone
FEATURES4.0AUDIO QUALITY3.5EASE OF USE3.5VALUE4.0
RATING PRODUCTS FROM 1 TO 5
PROS: Lightweight. Good sound quality. Good value. Comes in storage box with cable, windscreen, and clipmount.
CONS: Somewhat noisy. No internal battery option (requires phantom power). Requires balanced-line transformers for connecting to unbalanced inputs.
Shotgun stereo mics typically employ a mid-side (M-S) stereo-pickup design with the requisite two capsules contained in a single compact housing. That is a much more elegant solution than, say, grafting together two interference tube mics to create an XY stereo pickup pattern (not to mention an unwieldy V-shaped monstrosity). In a dedicated M-S mic, the mid capsule (directional or omnidirectional) points straight at the sound source, and the “side” capsule (bidirectional or figure-8) is positioned directly behind the first cap, with its two diaphragms aimed to either side. By means of an M-S decoding circuit, the mid and side mics' signals combine to form a stereo image.
Typically, dedicated M-S mics have the necessary stereo-decoding circuitry built-in. On the AT835ST, you can also disable the decoder and record the shotgun signal on one channel and the figure-8 on the other. During post-production, that lets you create a variable-width stereo image by running the signals through a software- or hardware-based M-S decoder. A variable-width image offers creative advantages over a fixed-stereo image. For example, if you were mixing sound for video, you could widen the stereo image as the camera pulled back from a close-up, increasing ambience to match the broadening picture.
The quality of stereo imaging provided by an M-S microphone depends in large part on the directionality of the middle mic (or capsule). Whereas the omni or cardioid microphone typically used in an M-S setup provides natural imaging, the highly directional mid capsule of a shotgun mic makes for a noticeable compromise. Specifically, the resulting stereo image is weighted toward the center and sides with areas between those points difficult to pin down precisely. In addition, an M-S shotgun's mid mic leads to some left-right ambiguity when sounds move behind the mic. For example, a car approaching from your left and passing behind and to your right will generate some signal in the left as well as the right channel.
Elementfixed-charge backplate, permanently polarized condenser (electret)Diaphragm½" gold-sputtered MylarPolar Patternsline cardioid; figure-8 (for M-S)Frequency Response40 Hz-20 kHzDynamic Range101 dB (mid); 101 dB (side); 102 dB (L/R stereo)Sensitivity (@1 kHz)mV/Pa 31.6 (mid); 19.9 (side); 15.8 (L/R stereo)Signal-to-Noise Ratio (@ 1 kHz)72 dB (mid); 68 dB (side); 70 dB (L/R stereo)Self-Noise22 dBA (mid); 26 dBA (side); 24 dBA (L/R stereo)Maximum SPL (for 1% THD)123 dB (mid); 127 dB (side); 126 dB (L/R stereo)Highpass Filter80 Hz (12 dB/octave)Stereo Settings (switchable)M-S; L/R stereo-wide; L/R stereo-narrowPower11-52 VDC phantom powerDimensions9.29" (L) × 0.83" (D)Weight0.23 lbs.
I SAID SHOTGUN
A shotgun mic's pinpoint accuracy is achieved largely by physical design. The capsule is housed in a long tube with slots cut along its length. Those slots add acoustical delays to off-axis sounds. Sounds coming straight down the barrel combine with the time-delayed off-axis signals, resulting in acoustical phase cancellation at the microphone's diaphragm. The result is an extremely directional pickup — of higher frequencies, at least; the pattern naturally widens at lower frequencies.
Although some instances call for shotgun mics to be mounted on microphone stands, they're often handheld, mounted on the end of a boom pole, or clamped onto a video camera. In the last three cases, handling noise is an important concern. If the microphone is accidentally bumped or rubbed, some mechanical shock will reach the capsule and end up on the recording. The amount of that noise depends on the quality of the microphone's internal shockmounting.
Another type of handling noise is infrasonic noise, a powerful low-frequency shudder that happens when a mic is moved quickly, sometimes even when a shockmount is used. You can partially combat both types of handling noise and wind noise with a low-cut filter (assuming one is available). That approach is used at the expense of low frequencies in the recording. A better solution is to use a windscreen with an integrated suspension mount.