AES Journal Forum

It is a puzzlement to me. With this work I sought only to offer some data to help people know what to listen for when they make these adjustments. The article never claims to provide the single correct answer. The article never suggests one shouldn't listen to the sound. For me, this data helps make the searching-while-listening process a little more focused, more linear, more productive, and a little less random. It is hoped at least some other readers experience a similar result.

The preamp was left in the system under test so that consistent measurements could be made (and were made, but not included here) across a broad range of guitar amps, some of which have no effects send. The tone was deliberately clean, so the preamp was not causing overdrive and was only minimally coloring the measurements. The intent is to keep the system under test as close to a real world use of the guitar amp as possible, while making it as close to linear and time invariant as possible. It is a compromise for sure, but it makes the right trade-off, in my opinion.

The impedance was changed with a Jensen transformer which measures pretty darn flat above and below the bandwidth of the guitar.

Regarding my missing the forest for the trees, I can only wonder what Dallas would have me do. The three orthogonal placement variables are measured one at a time to better inform the reader when they place a microphone anywhere in a session. The reader is expected to integrate the three observations when working in 3 dimensional space. I agree with Dallas that, "Off-axis mic positioning therefore can result in a wide variety of tonal color even if the mic's off-axis EQ response is ruler flat." The article tries to empower us to master the process, so that within 'the wide variety of tonal colors,' we can find the one the guitarist wants, the one the composer wants, the one that suits the mix.

An off-center microphone can of course be angled, and often is. It might be angled back toward center, away from center, up, down, or off at any angle - there are an infinite number of possibilities here. The intended thought process was that one could - in any order - work the microphone out along any radius away from center, listening carefully; angle the microphone, listening carefully; and pull it back, listening carefully . For an off-center placement where one angles the microphone so that it looks back toward center, one should find it informative to note that the directional microphone facing back toward center is 'looking' back at - oh, there it is - the data reported in the dead center measurement.

The intent wasn't to find the best microphone placement for electric guitar; no such placement exists. The intent was never to measure the 'typical' placement of a microphone on electric guitar; one person's 'typical' is another person's 'WTF?.' The point was to begin to quantify the three primary placement drivers of tone individually so that one could more effectively suss out the tonal impact of complex changes to microphone placement, and so that one might explore more unusual placements in search of tune-motivated unique tones on future projects.

It's messy. The variables overlap. But doesn't this shed some light on an otherwise mysterious ritual? And isn't some data, interpreted with care and recognition of its limits, better than no data?

When we discuss guitarist's perception of their guitar cab sound, I hope we remember that the cab is typically on the floor and the guitarist's ears are at standing or seated height somewhere between 90 degrees off-axis to the loudspeaker cone(s) but rarely if ever on-axis, and that the ears are a stereo pickup also receiving a portion of room reverberant field input. Make of that what you will when selecting mic type and location.

When recording acoustic guitar, historically, I have noted that performers never get to hear their own instrument as an audience (or microphone) hears it, because their ears are typically more than 75 degrees off-axis to the sound hole(s) and top of the instrument, and their reaction to recordings is as one might expect, that the sound is too bright.

Here again, experimentation or simply multiple miking of instruments can shorten the time needed to make a mix choice, but in the case of acoustic guitar miking, never would microphone data be helpful in any way, beyond the study and mental cataloging that should have been done by any engineer with regard to microphones they might employ, and the spec sheet frequency response curves and polar data they may offer, long before the engineer attempts setting up a recording session.

We may also quantify the time needed for miking when we see a veteran engineer set up a nine-piece bluegrass music group in ten minutes, contrasted with a novice engineer who might require 90 minutes to assess and address the same situation—an example from direct experience--or by watching a $10/hour sound tech spend 20 minutes placing microphones in a foot drum for a House Of Blues show, and waste an entire sound check, which is sadly, more typical than extraordinary.

With respect to live sound miking in particular, it is also worth noting that most of the $10/hour sound techs working today, even in noteworthy venues such as House Of Blues, Whiskey A Go Go, etc., are not even aware of an Audio Engineering Society's existence, or what the terms "cardioid" or "directional" refer to with respect to microphones, begging the question of what any revelatory measurements or data can provide them, unless of course we are in industry where educated audio engineers work for $10/hour in 130 dB long-term environments, for audiences who don't care about good sound.

Still we should all appreciate Alex's tilting at windmills simply because of the value and ethics of providing any education or enlightenment, even if only a few individuals benefit from it over time. I have several former students who among other things have taken such information and become leaders in their field, one, chief of recording production for KUSC radio at Disney Hall in Los Angeles, another chief of operations for concerts and events for the city of Arlington, Virginia.

One final note; I have experimented successfully with the inclusion of a miniature electret microphone (Panasonic WM-61A, 6 mm omni), secured directly to the rear frames of guitar amp loudspeakers, powered by a 0.5 mA pick-off from the amplifier and fed to an XL male mic connector provided for instant cab miking use. With a little experimentation, a suitable location can be found and consistent results achieved for that particular cab. Total cost of parts is less than $5 and takes only a few minutes to install.

Nice work Andrew!
And thank you, BBC.

-Alex