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Freq question for cdennyb
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DanielB
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May 23, 2012 - 6:23 am
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Your charts are interesting, but I'm trying to get my head around the information they show. So I thought I'd ask a few questions.

I'm not sure what sort of an analysis you are doing.  Myself, I usually use a simple FFT chart that just plots amplitudes of the different frequencies.  Crude, but useful enough for the sort of tinkering I do.  

Is the frequency units actually in Hz?   That's what it is labeled, but that would mean the charts are showing just the frequency data below somewhere around the A note on the low G string.  I can see where that range could be very interesting considering the in-depth study of bridges you have been doing.  But wouldn't it be leaving off all the higher harmonic and sympathetic vibrations that make up what most people think of as the tone of the instrument?

I'll show the sort of chart I usually use, for comparison.

Screenshot.pngImage Enlarger

That is just a quick comparison of a single note, the low G on FM's violin (from his tutorial on how to draw a bow across the strings) and the same note on my electric.  It is really a lousy choice for a comparison, since comparing even a close miked acoustic violin with the same violin at even 5 ft away is like comparing apples and oranges.  And an e-violin with a piezo pickup is so far from either that it may as well be a banana.  But I can tell some things from it.

FM's chart (the top one) has considerably more harmonic content, because it has a more complex tone.  Mine is recorded direct, so the fundamental at about G 196 is louder, while his first harmonic (G 392) is actually louder in the recording than the fundamental.  That alone would give his instrument a higher timbre and a more "singing" tone.  If I look in the volume range down to about -48 db, FM's has considerably more octave and musically related intervals than mine, so it is pretty obvious why the tone will be more complex.  For example, note the little "bump" his chart has at about D 293?  That is his D string starting to "sing along" with the G.  If I didn't already know he was playing an acoustic instrument, that would be a clue to indicate it right there.  His soundpost may have been adjusted at some point to strengthen the D a little, or the body of his violin may favor D a bit just from the size and shape of the violin, I don't know enough about violins in general to know if that is unusual.  We do not see a bump at the other open strings around A 440 or E 659, though, so it appears to be an intentional characteristic.

Also he has a lot going on above 5000 Hz, which would make his overall tone with that violin much more "open" sounding than my electric.  Comparatively, the electric will sound "muffled" or dull without at least some adjustment to eq and etc.

That information would be at least a start for a sound engineer who wanted to make the sound of an e-violin more closely resemble FM's sound (or vice versa).  There is only so much one can tell from one note on an open string, of course. 

I made most of those observations on frequencies which are higher than what your charts seem to be set up to show, though.  It may be that I don't understand what your charts are showing, exactly, or maybe I don't know enough about reading frequency charts but it seemed unusual to me, so I thought I'd ask about the frequency range we're seeing as it is labeled on the charts you do.  

It is not that I don't appreciate the chart you did for me and don't find the assorted comparison charts interesting.  I do.  But I'm trying to understand what is being shown so I can maybe figure out how to get usable info from them.

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"This young wine may have a lot of tannins now, but in 5 or 10 years it is going to be spectacular, despite the fact that right now it tastes like crude oil. You know this is how it is supposed to taste at this stage of development." ~ Itzhak Perlman

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Oliver
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May 23, 2012 - 7:51 am
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Yeah, I'm also more used to the simple FFT chart.

You say "5 feet away" regarding the possible ways to record a violin (type) instrument.  Do you have any notion on how far away is needed to truly characterize a violin ? 

So far, I'm finding the sound is better off to my right .... call it 45 degrees.  Yet, most guys are playing right into a very close stage mic where my "under the chin" noise makes a horrible racket ?  (And I have no idea how the little clamp-on mics work?)

coffee2

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DanielB
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May 23, 2012 - 8:26 am
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Well, it would depend on that you mean by truly characterizing it, Oliver.

If you want it to sound on a recording like it sounds to you when you're playing it, you'd want to mic it very close.  Like take your little lapel mic and clip it to the brim of a hat and wear the hat, perhaps.   If you really wanted it to be like it sounds to you when you are playing, you'd also have to kick up the low and mid frequencies a little with some equalization, because part of what you hear when you play a violin you hear by bone conduction through the collarbone and jaw.   You could probably get at least close to it with that.

But to hear it like a listener would hear it is a bit more complicated.  You'd want at least stereo recording to catch some of the natural ambiance of the place where you are playing and to catch some of the complexity that makes a violin such an interesting instrument to listen to in person.  Assuming a listener would be nearby and in the same room, 5 to 8 ft away with 2 microphones could probably at least make a good start on it.  Put the microphones maybe 4 ft apart to make something that at least sort of imitates hearing it with two ears. 

The problem would be that it would pretty much take a mixing board or some recorder other than going direct into the computer, though.  Computer mic inputs are mono.  They look like the stereo plug for the headphones, but one of the conductors carries power to the condenser mic instead of sound.  On the good side, though, there's quite a lot of old tape recording decks going cheap used at yard sales and second hand store every day from the 70s and 80s that have a mic input for both right and left, often dual meters as well.  Record on one of those and then use a stereo cable to get it into the line input of your soundcard and it can be less expensive than setting up with even a small mixing board.

That's what I'd try for starters, anyway.

"This young wine may have a lot of tannins now, but in 5 or 10 years it is going to be spectacular, despite the fact that right now it tastes like crude oil. You know this is how it is supposed to taste at this stage of development." ~ Itzhak Perlman

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Oliver
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May 23, 2012 - 8:45 am
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That's helpful. 

I was amazed on a previous  occasion how much effect there was for vinyl floor vs. carpeted room !

I sometimes use Audacity for hi/low bandpass filtering but a close friend and dealer told me that I can only hear my violin if someone else is playing it !

coffee2

When you come to a fork in the road, take it.

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