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Recording Electric Guitar—The Science and the Myth

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[Feature] Electric guitar tone, you know it’s right when you hear it. How is it achieved? The typical starting approach at the guitar amp: Shure SM57 microphone, slightly off center of one of the cones of a driver, up close and almost touching the grille cloth. Oh, and angle the microphone a little. Ask veteran engineers why this microphone placement strategy is so common and a range of justifications follows, from seemingly scientific explanations, to vague guesses, to an honest, “I have no idea. I’ve always done it that way. Everyone does.”

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JAES Volume 58 Issue 1/2 pp. 80-83; January 2010
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Marshall Guerra
Comment posted February 16, 2010 @ 14:54:37 UTC (Comment permalink)

Great article. I can't wait for the results of the subjective evaluations. If this gets presented at a conference, it would be really helpful to have sound files in addition to the graphs. I work in diesel engine noise and vibration and a sound file is worth a thousand graphs. I assume that is even more true in the recording business.

In the section about the off-center placement of the mic, there was mention of the cardioid-like radiation pattern of the amp but I didn't see mention of the cardioid response of the mic. Maybe it was just obvious to the intended audience, but the response of the mic in conjunction with the response of the loudspeaker resulted in the attenuation of high frequency. Had the test been performed with an omni-directional (flat frequency respnse) micrphone, I believe the high frequency attenuation would have been less pronounced. I realize that would not be a real life recording situation and the room reflections would be an issue but it's something to think about.

Anyway, I really enjoyed the paper and I would love to see more work like this. There could be a whole series of "Science and Myth" articles. There I said it, I want to see more protractors in the recording studio.


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Timothy Burke
Comment posted February 16, 2010 @ 19:07:32 UTC (Comment permalink)

I liked the article as well, a good start. I have been starting to do some recording myself and the techniques described are ubiquitously recommended on the various recording boards on the net, and also by local engineers I have talked to about recording guitar. The article does tend to ignore the issue of linearity though. Loudspeakers are not linear, and neither are tube amps. The measurement techniques and graphs essentially make the assumption that the guitar amp is a linear time invariant system, which is not entirely true. I am wondering what the impact of the microphone placement is on the harmonic content added by the guitar amp and loudspeaker. Through experimentation and experience I have come to believe that the loudspeakers play a very significant role in guitar tone. I would also challenge the assertion that the higher frequency content is not perceptible. Very subtle changes in guitar tone that are hard to even put into words can definitely be heard by some players, myself included. Perceptibility also depends a lot on the type of guitar tone you are going for, clean, dirty, lots of effects, etc. At the end of the day, what is important is how easy it is to get the guitar to sit in the final mix correctly and be heard, without stepping on other instruments. An article addressing loudspeaker linearity, impact on tone, and how the raw tracks fit into the final mix would be the next step in my mind.


Alex Case
Author Response
Alex Case
Comment posted February 17, 2010 @ 19:22:34 UTC (Comment permalink)

Marshall,

I like the logic:
A picture is worth 1,000 words.
A sound file is worth 1,000 pictures.
Therefore
A sound file is worth 1,000,000 words. Audio wins.

Regarding the microphone pick-up pattern, you've got it exactly correct. Both the directionality of the microphone and the loudspeaker are in play here. While an omni microphone would rule out the SM57s cardioid-contribution to the measurements, it was a mission of this project to begin to quantify typical recording practice, based on the most common electric guitar starting point. So the measurement microphone was a 57, and the stated results are for the whole system, not just the amp.


Timothy,

You are exactly correct regarding non-linearity and time invariance. The piece tried to point out that a 'clean' guitar tone was used - very much to minimize the issue you raise. It's imperfect, of course, but the results may be viewed with a grain of (non-linear) salt. The whole system is wonderfully non-linear, the transducers and the electronics - the pick-ups, loudspeakers, and the tubes.

I should mention that the test was kept relatively tolerant of non-linearities by using a swept sine wave. So at least the harmonic components are minimized in the results.

Regarding perception, I welcome your comments and I share your point of view that there are many attributes of tone that guitarists and engineers seek out and savor that eek up above the upper middle frequencies. But the only way to know for sure is to do the subjective studies.
:-)


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Andrew Munro
Comment posted February 20, 2010 @ 23:03:37 UTC (Comment permalink)

This article reminds me of my time as an engineer with Shure Bothers UK. My job involved going out with bands such as the Rolling Stones and Led Zepplin just to help the crew get the best live sound possible. I have some great shots of Jimmy Page's set-up (4 mikes on one cab!) if they can be added to the site.

Keep up the good work.

Andy Munro

Munro Acoustics

London


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Andrew Munro
Comment posted February 22, 2010 @ 15:25:45 UTC (Comment permalink)

Woops- its Led Zeppelin! Is it possible to post pictures?


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Timothy Burke
Comment posted February 22, 2010 @ 19:00:41 UTC (Comment permalink)

Hey Andy,

WOW. Sounds like a pretty cool job! I would love to see the pics, even if you can't post them here. You could use one of the free image server sites like Photobucket or Image shack, make an album and post a link?

I read a drum book recently that was talking about 3 microphone techniques for micing the drums, and was talking about a method of micing the snare and kick and then placing the third mic that off to the side and behind ~6ft the floor tom. Allegedly this method was stumbled across when Zep was in the studio and a recording tech accidentally bumped the mic and it swung around, and everyone in the control room was shocked when a giant drum sound emerged from the monitors.

I know I have often wondered how Page got some of the guitar tones on the early albums, particularly when options were so limited compared to today. Perhaps this is more legend than fact, but from the stories it sounds like Zeppelin was really pushing recording techniques forward back in the day.


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Joe Hancock
Comment posted February 24, 2010 @ 19:00:21 UTC (Comment permalink)

Hey guys,This whole discussion has omitted the ART factor. Recording technics are going to change with the variation of any one or more of a set of variables.
A recording engineer should seek the particular tone that the artist wants to hear in the "sound pallette". Linearity is not a word I recall as used very ooften in tracking sessions. I believe Jimmy Page as an engineer was brilliant as an experimentalist, finding the optimal results in his given environment,for his client Jimmy Page. Mic placement IS premium EQ!!


Alex Case
Author Response
Alex Case
Comment posted February 25, 2010 @ 19:17:21 UTC (Comment permalink)

Hey Joe,

The whole point of the JAES article was to shed light on the ART factor. Mic selection and mic placement are indeed EQ, and the research published here quantifies the spectral impact of the most common placement variables. We are trying to bring order and intuition to a very creative and non-linear process - less guesswork and more deliberate action; less superstition and more science.


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Joe Hancock
Comment posted February 27, 2010 @ 15:37:30 UTC (Comment permalink)

Thank you Alex, for your reply.

I have often wondered how magnetics—flux fields, polarities, current induced field effect, ect.. of two electro magnetic systems( speaker and mic) interact.
In that a microphone and a speaker are virtually the same electrical device, does the positive pole of the permanent magnet present to the positive of the other device? I have often thought this might be why off axis mic'ing often proves to be a smoother sound IMO. The mechanical relationship of the two diaphrams is easy to comprehend, but should be optimal when squared up, dead center.(just seems to me) As soon as we drive a couple amps of current across the speaker coil we're confronted a whole new set of Phun Fizikz Phaktors. N.O.W--- Flip the polarity on 1(one) permanent magnet. What now??

Respectfully submitted with a headache
Joe Hancock


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Timothy Burke
Comment posted February 27, 2010 @ 13:45:57 UTC (Comment permalink)

Joe, I agree with you in the sense that when you are recording, you are going for a sound. I'll break any "rule" as long as the end results are what I'm looking for. But when you face a challenge such as instrument X just "isn't sitting in the mix right," and your looking for something else to try, having data can help reduce the time it takes to get what your looking for. There are so many variables, I appreciate knowing what moving a mic away or off axis of a driver is actually doing. I'm still going to listen to it when recording, but I feel it is helpful to me. Ultimately experimentation is the only way to go, that or experience, which is usually gained by lots of past experimentation.


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