Here's a couple of files. To keep it very simple I struck a single note...the C, 1st fret B string. I did this because over time I have narrowed the problem down to this note as the main offender. Not the only offender...but the main offender. For example, the C# note, 2nd fret B string has no such problem. The open B string has no such problem.
A word on the 2 examples (same guitar, same recording):
Guitar A - Only the note in question played, no EQ or manipulation
Guitar B - Only the note in question played but at the start of the clip I have a narrow Q at 796hz (note is G5) in place to reduce the problem by 15db. As the clip plays I gradually reintroduce the problem by slowly bring up the 15db back to 0 so the clip is back to normal. Later in the clip I reduce that 796hz again by -15db and then reintroduce it again.
So the problem I am hearing is at 796hz. There is an "overtone" (or whatever you want to call it) ringing a G5 note. This is 100% not the room or the microphone or anything else like that. It comes directly from the guitar. It is baked into the guitar. This is what the naked ear hears. As you can imagine...playing any chord with that 1st fret B string note involved creates complex problems. I hope and trust you can hear the problem just from striking the single note itself as in the examples. Since an acoustic guitar produces a very complex combination of sounds...when that C note is part of a chord it creates big problems. I can EQ the problem away to some extent at 796hz when striking the single note...but when the problem is part of chords...this complex combo of strings, notes and sounds it is not easy to get rid of.
I guess I'd recommend headphones for this with a suitable volume. But good speakers will show it too.
