Tips, Techniques, Examples about my favorite musical instrument, the Twelve-String Guitar.

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Wednesday, February 28, 2007

Hiding From the Whomp

The whomp never really left despite all my efforts. I managed to reduce it some by spreading the microphones far away from the sound hole, but it was still pretty obvious, particularly in the Lute prelude, BWV999 that I was working on. It dawned on me that maybe raising or lowering the tuning of the guitar would avoid the whomp, a sound that seemed to be pitched at 91 hertz. With the Taylor LKSM tuned down a minor third the open 5th course was right at this frequency. First I raised the pitch a semitone by capo-ing the first fret. This didn't help a lot. It was now emphasized on the fourth fret of the 6th course, but it was still in evidence on the open 5th. Next I tried lowering one semitone, so it is down a full third. This seemed to change it for the better. It made the notes on the open 5th course sound sharper and more defined...not so much a whomp.

Below are screen shots of the wave diagrams of the part of the prelude that has an A pedal. In the wave diagrams, the vertical axis is volume and the horizontal axis is time. The upper diagram is with the guitar tuned down a major third and the lower one is with it tuned down a minor third. You can easily see the pedal notes on the 5th course; they stand out about twice the volume of the other notes. The notes on the 5th course are the parts of the blue that stick out above and below - you can count about 12 in the top one and 11 in the bottom (apparently I played one of the bass notes softly in the second piece shown here).

If we zoom in on 3 of the notes you can see the sharper peaks and quicker roll-off in the top diagram; it is from the guitar tuned down a major third. The bottom one, with the rounded attack and slow release is the guitar tuned down a minor third.

I've posted both of these fragments on soundclick, and I think you can hear the difference.
The major third is here.
The minor third is here.

I'm still baffled by this problem. The LKSM is designed to be tuned down a minor third, but that is exactly when the problem is most noticeable. It may be that I need more room treatment. From what I have read, room reflections can occur at many more frequencies than just those produced by room dimension nodes. Before I spend hundreds more dollars on room treatment, I plan to test out this theory by
  1. recording in another room
  2. recording outdoors
For now I've moved the problem note from a much used open 5th course to a seldom used 4th fret of the 6th course, but this is avoiding the problem, not solving it. There should be a better solution.

Note: wave and spectrum diagrams are from Audacity.

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