EQ Resonance

E

ecs113

New member
I recorded a friend playing acoustic guitar tonight. While editing the clip (for practice, learning and experience), I noticed a "ringing" (resonance?) at a certain frequency. I determined the frequency to be around 932Hz, which corresponds to B (note: he often played chords including the open B string). I notch cut at 932Hz and listened again; it sound MUCH better. I noticed another "ringing" frequency, and I made an educated guess that it was around 466Hz (another B), which it was. I notched that, and again, it sounded much better.

I used an MXL 2001 about a foot away from the sound hole (is that the problem, the fact that it was aimed at the sound hole, thus the resonance?).

I am new to recording and want to learn the nature of this discovery. What is the meaning of this octave resonance? Would I find that if I cut more octaves of B, it would sound even better? What is the source of this problem?

Thank you in advance. Yes, I did a search (for: octave + frequency) and could find nothing specific.
 
Comb

Oh yeah, I noticed that if I kept notching at the octaves, the result would resemble a comb filter. Is this correct?
 
Well, my understanding is that you're dealing with overtones of a powerful tone. The B is really strong on your friend's guitar.

Notching is fine if there's a bad problem sound, but let me share something with you. I learned how to sweep frequencies looking for unpleasant sounds at particular frequencies, and so I went to town and starting doing it with every track I recorded. Got some good results. Okay. One day, after I'd notched a number of frequencies on a number of tracks in a particular song, I happened by accident to play the orginal version of the song *before* I'd started mixing and notching. The original sounded *clearly* better.

I'm not saying don't notch. I'm saying don't notch if you don't absolutely have to. Every time you notch, it takes something away. It's cosmetic surgery, not enhancement.
 
It is not uncommon for a problem frequency to have another problem frequency at octave intervals. Sometimes, it could be an octave and fifth, or forth, or seventh, etc.

Look up the Overtone Series. That is what you are referring too. Stringed instruments display VERY strong overtones that usually follow the overtone series quite nicely if the guitar is well constructed.

Overtones are what give the instrument is Timbre. When you play the fundamental note (and on guitars, it is an octave lower than what you think it is usually...the low E on a guitar has a fundamental of 83Hz) you also have a very strong first octave (that same 83Hz fundamental will have a VERY strong 166Hz), and less stronger second octave (332Hz), then you start getting into the 4th's, 5th's, 7th's, still more octave, etc.

That mic isn't considered to be the tightest mic in the world, so it may be sympathetic to certain frequencies. Also, other electronics involved may be sympathetic to certain frequencies. Your ROOM may be sympathetic to certain frequecies too. It could be any number of things. But, it could just be that the guitar itself has a very strong B note!

Read up on the Overtone Series and also the Fletcher/Munson Relative Loudness curves. Both will give you an idea about WHAT you actually hear in relation to relative loudness.

Ed
 
I am familiar with harmonics, overtones, partials. Just wanted to know how to file this phenomenon in my mental recording filing cabinet.

I considered not notching, leaving the resonance in, but after multiple plays it seemed really distracting from the rest of the music. I guess that's what it's all about: weighing the advantages and disadvantages.

Thanks for you replies and tips.
 
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