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Wednesday, October 23, 2013

Retro Recording Review!
A Classic Benchmark in Microphone Accuracy:
The Shure SM81 Small-Diaphragm Condenser

Price: $436 retail
Likes: Accurate cardioid pickup
Dislikes: Omni capsule no longer made
More info: Shure SM81

by John Gatski

  If ever there was a gem of a recording microphone it has to be the SM81. Introduced in 1978, this compact cardioid has carved its reputation as a quality recording transducer for almost any instrument — from piano to drums, overheads to acoustic guitar and classical stringed instruments. Countless recordings have been done via the SM81, yet it often does not get the attention of more famous mics, like the Neumann U47 or even Shure’s ubiquitous SM57.
  The SM81’s main asset is that it has a very accurate frequency response. Unlike many of today’s instrument mics that have various boost curves in the treble, the SM81 is almost flat, varying but only a dB in the high midrange/low treble range. This response is perfect for those recording projects where you don’t want a boost, cut or any other response tailoring via the electronics. That is why numerous engineers have used the SM81 as drum cymbal overheads; the response is smooth and natural without the splashiness of mics that are hyped up a few dBs in the treble.

Delightfully simple...
  The small-diaphragm, cardioid-pattern, electret condenser SM81 has continually been in production since the late 1970s, when it originally sold for $200. Today, it sells for $436. Originally, made in the USA, the SM81, like many Shure mics, are assembled in its Juarez, Mexico plant. It is now  It has been refined over the years to lower its noise floor and once was available with an optional omni-directional capsule. The body dimensions also have been altered slightly — with the older versions tapered toward the termination end and the later versions symetrically round from one end to the other. The SM81  features a three-way bass roll-off switch (O dB, -6 dB or -18 dB per octave at 200 Hz) and an attenuation switch (O dB, -10 dB).)
  The mic is a bit longer than many smaller, modern instrument condensers, at more than 7.5 inches, but it comes with its own mount (and wind screen) that attaches easily to a T-bar stand or other typical mic mounting devices. BTW, the SM81s are so consistent in spec that Shure does not have to level match. They are usually very close in output right out of the box.

Amazingly flat frequency response with the bass roll-off disengaged

  As mentioned, the key to its sonic signature is the flat frequency response. If you look at the factory response graph, it varies only 1 dB at any point from 50 Hz to 16 kHz — an amazing spec. that many of today’s microphones don’t mimic. In that crucial 5 kHz to 10 kHz range, the response is almost ruler flat. If you have a neutral recording space and you like the sound of the instruments, this sonic accuracy makes for a truer recording that is especially appreciated when recording in high resolution formats. The defunct omni-directional capsule option retained the cardioid’s accuracy, but offered more of an open recording pattern to pick up more of the room. The omnis are highly sought after today.
  The knock on the SM81 has been its self-noise spec. In fact, over the years there have been modifications made through third parties to lower its noise. The original spec was 17 dB self noise, which was later lowered to 16 dB A-weighted. Most of today's small condensers are a few dB quieter, but in the real world, I really don’t notice any extra noise — even in 24-bit.

Presence enhancement, courtesy of the microphone, is not desired when I want an accurate portrayal of my guitars. The SM81 is truer to the guitar’s actual sound in a good-sounding room.

  When I asked longtime recording engineer Tom Jung about his extensive use of the SM81 during the 1980s and 1990s, he said its accuracy was paramount in the early days of digital recording where you did not want any added harshness through the microphone.
 Jung also noted that Shure used to supply him with modified versions (in omni and cardioid) that were several decibels quieter than the stock ones. (Per Shure this custom modification activity is no longer being done). Jung said the SM81 excelled on piano and drums, but he would often use it on all sorts of instruments, including bass and guitar. At one point, Jung remembers having a dozen SM81s in his arsenal.

A fresh take on the SM81
  I recently acquired an SM81 pair from Shure to reacquaint myself with the mic. Since I record mostly acoustic and electric guitar, I went to town, recording several six strings and amp combos. I recorded to 24-bit/192 via a TASCAM DVRA-1000-HD, which was fed by a stereo True P2 discrete mic preamplifier, using WireWorld XLR cables.
  On a custom Guild F47 rosewood edition with red spruce top, I recorded at 24 bit/192, using the True P2 discrete mic preamp. I immediately noticed how accurate the playback was. The Guild sounded like it did live! No enhanced strumming or picked-sound lift in the high midrange and low treble. No presence boost at all. Also, the bass proximity effect was typical of a small condenser in that you could easily control with distance placement. Thus, I did not have to apply any electronic roll-off. The recorded results were similar with my big Martin J-40 and my custom OO-28V finger-style guitar. They sounded exactly like what I hear when someone plays them.

A SM81 manual from the early 1980s

  In contrast, the Audio-Technica 4051B and Shure‘s more recent KSM141 instrument microphone added a gentle presence sheen to the guitar’s treble spectrum — a sound that can match up well with darker sounding guitars and/or rooms. But that presence enhancement is not desired when I want an accurate portrayal of my guitars. The SM81 is truer to the guitar’s actual sound in a good-sounding room.
  I also was quite happy with the SM81s on jazz guitar. My Gibson L5-CES, with twin humbuckers, played through my original Fender Deluxe Reverb, has a warm, bell-like strummed tone that is mostly upper bass/midrange/lower treble focused. In recording the combo with the SM81, its mellow character with a hint of top-end was true to the actual sound of amp and guitar. I also noticed how dynamic the sound was in 24-bit. With the noise of the old Fender (even with a fresh cap and resistor upgrade), any self-noise from the SM81 was not audible.

In the right key...
  I also mic’d up my electronic Nord Electro 3 keyboard, through the ultra accurate Lipinski L-505s loudspeakers, to hear how the Nord’s excellent Steinway mode sounded through the ‘81s. As expected, the sound was exactly like the played-live tone through the speakers: no low-treble tilt in the high register of the sampled piano, a characteristic I have noticed when recording with other modern instrument mics. Again, in my book accuracy is key.
  In light of the hyped character of many mics used today for recording various instruments, some engineers may say the SM81 tone is boring, lacks flair or any character. But that is exactly why I love it. I hope they keep making it forever.

Second Opinion!
Classical Music Recording Engineer
Likes His SM81s, Shure Product Support

  The Shure SM81 is a standard in the audio industry — if ever there was one! Everyone has an SM81 story; here's mine.
  A couple of summers ago, at a music camp in Vermont my daughter was attending, I was asked to check out their four hanging mics for which, it turned out, I had given the original advice about purchasing decades ago. They had a pair of Sony ECM 33Ps, and a pair of Shure SM81s. The Sony’s had been there since I gave my original advice — which was during the mid-seventies; the Shures came a few years after that.
  All four mics were incredibly dusty and had never been taken down from their originally suspended perches in the wooden rafters of this very rustic building. Oh, I should point out that this was a summer music camp, and that the building is vacant, locked up tight, but unheated, every Vermont winter!
The camp director had decided to buy new microphones, and he said I could keep these old "beat-up" mics, if they were worth keeping. Gee, thanks, I guess. So I listened to the Shures and they sounded "okay," but not as good as when they were new. Remember, these mics were over thirty years old, and electret capsules do have a finite life.

The full SM81 microphone kit

  So I sent them back to Shure for repair. A few weeks later, I got a repair estimate, which seemed reasonable, so I submitted my credit card info. A few days later, I received a brand new pair of SM81s from Shure! Now there's a company that stands behind their products!
  Later that year, I managed to pick up a pair of the rare, no-longer-made, omnidirectional capsules for SM81s, which made them that much more useful in my recording endeavors. The omni capsules allow me to record acoustic guitars close up without proximity effect — if that's the sound I want — and I also can record choirs (another standard use for SM81s) using spaced omnis, instead of crossed cardioids.
  The SM81 is a bit longer than your average "pencil," small-diaphragm condenser mic, but it's probably one of the flattest-sounding cardioids ever made. They're really flat down to around 200 Hz, where they start to roll off in the diffuse field; used close up, there's that proximity effect, so you usually don't hear the same thinness you'd hear when used for distant miking.
  In my recording experience, the most common uses for the SM81 is as a pair on an acoustic guitar, or hanging a duo in front of a choir. Their neutral character really shines a light on good vocals and guitar pickers who have quality instruments. Many mics have come out since Shure introduced the SM81, but this 35-year old design is pretty hard to beat for those applications.
—Dr. Frederick Bashour

  Dr. Fred Bashour has been a classical recording engineer for the past 45 years, with recordings released on over twenty labels, including Musical Heritage Society, Naxos and Dorian. His studio, Dufay Digital Music, is located in Western Massachusetts. He holds a Yale Ph.D. in Music Theory and is also an gigging keyboardist. He can be reached via the Everything Audio Network,

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