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Audio-Technica AT835ST and AT815ST, April 2001
May 13, 2004 12:00 PM, By Ty Ford
STEREO SHOTGUN MICROPHONES
In the rapidly changing world of pro audio, taking things for granted may not be a good idea. If you think you know what to expect from a stereo shotgun mic, then you might accidentally dismiss Audio-Technica's 9-inch AT835ST ($899) and 15-inch AT815ST ($999). The most obvious thing about these two mics is that, in addition to being conventional shotgun mics, they offer both M/S (Mid/Side) and L/R stereo (with both narrow and wide L/R spreads).
Both mics come in a vinyl box with a mic clip, foam windscreen and a 5-pin XLR that plugs into the mic and splits into a pair of 3-pin XLRs. The diameter of each mic is slightly larger than a Sennheiser 416, but small enough to fit properly in a standard rubber, Rycote boom mount.
Both mics use the same two electret capsules; a front-facing line-cardioid “mid” capsule and a figure-8 “side” capsule mounted directly behind the mid capsule. Both mics require 11 to 52 VDC at 4mA phantom power. The longer AT815ST weighs less than five ounces and the AT835ST less than four ounces. This makes them well-targeted for the EFP/ENG video markets with their rapidly growing need for stereo ambient sound or any other stereo sound gathering application where weight is a factor.
Using the line-cardioid capsule only in M/S mode, I found the sensitivity of both A-T mics was 1 or 2 dB below my Sennheiser 416 and 816, and the A-T mics were heard a bit more off of the sides and to the rear. The level of self-noise was about the same, although the spectra of the self-noise was different. The Audio-Technica mics made sort of a “hiiiiiih” compared to the Sennheisers' “pfffffff.”
One very noticeable difference between these A-T mics and others I have used is in the design of the LF roll-off filters. The “flat” frequency response of the shorter AT835ST begins an LF roll-off at about 500 Hz and gently slopes down -3 dB at 70 Hz and remains there down to 30 Hz. Engaging the LF roll-off switch actually increases the LF response between 100 and 500 Hz. Below 100 Hz, it drops off more steeply at 12 dB/octave. This means you get more mid-bass and less low bass with the LF filter engaged.
The AT815ST “flat” response has a 3dB bump in the 30 to 50Hz range that returns to 0 dB at 100 Hz. Engaging the LF filter causes a 4dB increase between 100 and 400 Hz, which then drops off gently at about 10 dB/octave below 100 Hz. Again, engaging the LF filter causes an increase in upper bass and a decrease in low bass.
Both mics also have presence peaks slightly higher in frequency than that of the Sennheiser 416. The AT835ST begins a slow 2dB rise from 1 to about 2.5 kHz. It then achieves a +4dB plateau from 4 to 7 kHz, peaks at +5 dB between 8 and 9 kHz and slopes off moderately crossing 0 at 15 kHz before dropping down to -4 dB at 20 kHz.
The AT815ST begins a gentle rise at 1 kHz, hits +4 dB at 4 kHz, dips a decibel or two between 6 and 7 kHz, rises to +5 dB from 8 to 10 kHz, is back down to +3 dB at 15 kHz and slopes off to -1 dB at 20 kHz.
In their flat positions, both mics sound thinner than a 416 Sennheiser. With the LF filters engaged, the increase in upper bass makes them sound more similar. The 416 still has more beef in the upper bass and develops its presence peak a bit below that of the A-T mics, making them sound a bit “zippier” on top. In my short time with them, I found that I liked keeping them in the rolled off position to get that extra upper bass, while reducing the amount of low bass.
I did find that, in stereo operation, as a sound source works its way from front to rear, there's a point after the source gets past the side capsule where the mic gets a bit confused and throws the signal to the opposite side. As the sound source continues past the rear axis of the mic and heads back to the front on the other side, a similar “flip-flop” happens. This occurs in either L/R mode or in the M/S I matrixed in my Orban Audicy DAW. So if you're doing sound work at an automotive road rally, then it's probably not a good idea to set up in the middle of a couple of deep curves that result in the cars crossing the rear axis of the mic.
If you haven't considered M/S stereo, it's a handy format when you don't have a clue as to how wide you want the stereo image in the final mix. Although it's a bit difficult to listen to in the field unless you can convert it to L/R, being able to adjust the width in post-production is a definite advantage. If you're using zone mics, then you can use an M/S mic as a stereo center spot mic for soloists, using the matrixed mid-channel fader to adjust gain for the performer without upsetting the stereo balance of the side channels.
I took the AT835ST to “Open Stage” night at 8x10, a local music hot spot in Baltimore, where Craig Hopwood runs the house and mixes P.A. Through the 8x10 sound system, the AT835ST sounded a lot more open and clearer than the Shure Beta 58s. Adding a bit of EQ at the board around 3 to 4 kHz and 10 kHz made the Betas sound more similar.
Running the mic in L/R wide, I twisted it around 90° so it was aiming high and low, instead of L/R stereo. Pointing the mic at about the Adam's apple of a folk singer, I could get a split of more voice on one fader and more guitar on the other. In L/R, harmonized vocals with two singers each about a foot and a half away from the mic also worked well. When placed a foot away from an acoustic 12-string guitar, we got a nice image, but ran into feedback trouble when we added more instruments and had to crank up the stage monitors. Of course, in the studio or for on-location recording, feedback just isn't a problem.
WRAPPING IT UP
The AT835ST and AT815ST are lightweight mics with obvious EFP/ENG applications, especially with a tailored LF response that eliminates low end. Having an LF roll-off filter that increases the middle low frequencies and dumps the lower ones is a great idea that works out well in the real world. Having slightly “center-focused” stereo images means you'll get some stereo information, but nothing radical that could cause problems later. With their higher presence peaks and out of the way of blaring stage monitors, either mic might also find use as a stereo drum overhead.Audio-Technica U.S., www.audio-technica.com
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