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Frequency analysis violas

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15 hours ago, David Burgess said:

It will still highly depend on which notes were played.

When I want to do a "played" response graph, I mostly use glissandi, in an attempt to play all frenquecies equally.

Do you play the glissandi on all four strings?

Are they repeated or just one bowing?

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39 minutes ago, Marty Kasprzyk said:

1. Do you play the glissandi on all four strings?

2. Are they repeated or just one bowing?

1. Depends on what I'm looking for. When it comes to the frequencies over 4K, I like to set these aside, since I haven't run across evidence that anyone knows how to fine-tune these anyway.

2. My first choice would be to take multiple bowings, since so much can change from one bowing to another.

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On 12/27/2018 at 2:02 PM, David Burgess said:

1. Depends on what I'm looking for. When it comes to the frequencies over 4K, I like to set these aside, since I haven't run across evidence that anyone knows how to fine-tune these anyway.

>

I don't know how to control the frequencies over 4k either.  I suspect that the violin's roll off frequency is important.  It is often noted that at a "bridge hill" around 2500 to 3000Hz is desirable but my opinion (unsubstantiated of course) is that a steep cliff to the right of this hill is also important for avoiding unliked harshness.

Much of the violin research has concentrated on the low frequency end with the well known "signature modes" (A0, CBR, B1-, B1+ etc) looked at.  I think this is natural because we can easily recognize them and we have a tendency to work with things we can see.   

Conversely the high frequency resonances are a mess of overlapping identities and frequencies with no names.  Nobody wants to work with a bunch of no names.

 

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36 minutes ago, Marty Kasprzyk said:

Much of the violin research has concentrated on the low frequency end with the well known "signature modes" (A0, CBR, B1-, B1+ etc) looked at.  I think this is natural because we can easily recognize them and we have a tendency to work with things we can see.   

That has been one of my pet peeves for a long time, and it's even worse than "signature modes", but just the mode frequencies that seem to get the vast majority of the attention.  I grant that the frequencies matter, but the amplitudes have a huge impact on the tone, and I can't recall any substantial work on how to control that aspect.

37 minutes ago, Marty Kasprzyk said:

Conversely the high frequency resonances are a mess of overlapping identities and frequencies with no names.  Nobody wants to work with a bunch of no names.

I think it's pointless to try to look at individual modes in the higher ranges, but it is definitely a critical part of tone.  You don't have to work with names, but consider them to be sheep that might be herded in certain directions.

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18 hours ago, Don Noon said:

That has been one of my pet peeves for a long time, and it's even worse than "signature modes", but just the mode frequencies that seem to get the vast majority of the attention.  I grant that the frequencies matter, but the amplitudes have a huge impact on the tone, and I can't recall any substantial work on how to control that aspect.

I think it's pointless to try to look at individual modes in the higher ranges, but it is definitely a critical part of tone.  You don't have to work with names, but consider them to be sheep that might be herded in certain directions.

I am trying to get the higher frequencies - they depend a lot on the environment, one almost needs a sound isolated room - which I do not have. Any laptop fan in the background will add a signature. Higher frequencies from from frequency modulating power supplies (dimmable LEDs etc) all add to that sound spectrum. 

I work a lot with frequency analysis in science (I do something called NMR) and we would not accept a signal that does not have a signal to noise ratio of around 5 and is clearly reproducible.

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There is this article, www.jpschmidtviolins.com/Violin_Acoustics_2.pdf
which I think is by Don Noon, our fellow maestronetter. It refers to this average table in the Strad for the 'key modes' of Stradivarius violins (I attached a screen shot of the spread sheet). I wonder whether anything along these lines exists for violas. What viola sound are we looking for? I know what I like, they must not be 'nasal', I like a strong C-string, I like it if they also have an edge in the upper strings (whatever this means). I have hardly every seen a viola at an auction that I liked.1836963595_Screenshot2018-12-30at21_47_17.thumb.png.35e3b8d56a508121fe25ef4373e2f302.png

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One of the easiest ways I found to get a clear and fairly accurate response spectrum is to use an FFT app for your cell phone. These usually have the word "frequency" and "spectrum" in the title or description.

The app will have a clear, start and pause button. Clear the spectrum. Press start. The gently place the frog of the bow on a string and consistently draw it across the string with as little pressure as possible. With a finger, play glissando slowly up and down the string.

Do this repeatedly as many times as you wish and for each string. I find twice per string gives more than enough information.

Hit the pause button. Most have a feature to save the graph to a file.

I get clear peaks indicating the lower five or so prominent air and body modes, and a decently defined bridge hill.

Here is one from an average sounding but playable violin:

Spectrum_2018_12_31_14_03_00.thumb.jpg.d9576cef62414def1c2f25ad937ea096.jpg

 

 

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