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About ctanzio

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  1. ctanzio

    Tartini Tones

    A recent thread brought up the subject of Tartini tones. Some people thought they were an "illusion" due to some feature of the ear or brain. Actually, it is a response to an actual physical effect that is occurring in the sound wave. A Tartini tones can occur when two notes are played simultaneously. Due to periodic reinforcement and cancellation of the two sound waves with each other, additional pressure pulses may occur that the ear detects as additional tones. If the two notes have frequencies F1 and F2, then tones may be detected that have frequencies F2-F1 and F2+F1. If one generates two pure sine wave notes, say of 440Hz and 660Hz, then a very distinctive pulse can be seen with frequency 220Hz, the F2-F1 Tartini tone. As more overtones are added to the notes, it becomes increasingly difficult to distinguish the Tartini pulses from the note fundamentals and overtones. To illustrate the effect on a violin, I captured the sound of double stopped open A (440Hz) and E (660Hz) strings. The wave form appears as follows: You can see two distinct wave form shapes. The distance between similar shapes is the F2-F1 Tartini tone, or 220Hz. The distance between successive peaks is note F1, or 440Hz. The F2 note, 660Hz, is more difficult to pick out because of the periodic cancellation and reinforcement of the various overtones. An FFT analysis of the wave form detects both Tartini tones. The sound levels of the Tartini tones for the combination of complex sound patterns are much smaller than the note fundamentals and the first few overtones. This makes the Tartini tones difficult to detect unless the notes are being played very loudly. A more dramatic illustration can be done by combining pure sine waves.
  2. Fascinating to see it take shape. Thanks for posting a window into your workshop.
  3. The harmonic series is not a sequence of powers of two. It is a sequence of integers times the base frequency. Using an open A440 as an example: 1x440 = 440 The fundamental of the series 2x440 = 880 The first overtone of the series and also the first octave 3x440 = 1320 The second overtone of the series, but not an octave 4x440 = 1760 The third overtone of the series and also the second octave etc So there are many overtones of the harmonic series that are not octaves of the fundamental frequency. As Don spectral plot proves experimentally, the violin overtones, for all practical purposes, are integer multiples of the base frequency. So experiment and theory match. I would take technical exception with Michael Darnton's observations about "computed" FFT frequencies. FFT does not actually compute frequencies. Rather, it computes the contribution of each frequency across a large and detailed frequency spectrum that depends on the sampling rate (how many times per second the analog tone is captured as number) and the time span of the entire sample. If you convert a violin tone into a digital signal using a high sampling rate for several seconds, then the FFT algorithm can accurately compute the contribution to the signal of all frequencies in the spectrum range down to a very fine frequency resolution. Inharmonicity is the deviation of overtone frequencies from integer multiples of the fundamental. Effectively, this does not happen for a "well bowed" violin tone. If it does occur, a well sampled tone would display peaks at frequencies that are not integer multiples of the frequency of the first peak. It is possible that tones can sound "false" if the violin does a poor job of reproducing the fundamental and some of the lower octave overtones, or does a much better job reproducing the higher overtones than the lower ones. The overtone frequencies are accurate, they are just not very strong. I think what you are looking for is some general observation on what the strength of each overtone should be relative to the fundamental. Call this the overtone profile. I studied this a few years ago by sampling tones from various recordings of highly regarded violins. The note needs to be sustained for a second or so and played with no vibrato. Where the violin bow point was relative to the bridge affected the profile. The profiles of a good G string were quite different than that of a good E string. When comparing similar plots made of bad violins, I could usually tell why a bad violin sounded bad, but could not deduce any reliable rule as the why a good violin sounded good. Even if one could come up with a set of overtone profiles that many could agree gave a beautiful violin tone, it is not obvious to me how one can translate that into practical rules for making a violin.
  4. The refractive index is a bit high for use as a ground under common violin varnishes, and the crystals do not appear to be transparent. So the traditionally desirable values for these two important properties are missing. It is also highly soluble in water which may create other issues related to changes in humidity. Small amounts are deadly to swine and poisonous to humans. Trace amounts added to meats reacts with chemicals in the meat to give the food a pleasing pink color, and it also inhibits the growth of bacteria.
  5. ctanzio

    beware virus

    We should not be spreading false information about the vulnerability of MACs to viruses. There have been hundreds of thousands of MACs infected with malware. Since only about 10% of the personal computers in use are MACs, the brand has benefitted from being a less desirable target than a Windows machine because of the small market share. If you are a MAC user, use an anti-virus program. Keep your system software updated.
  6. If you are using the paste, you are probably putting it on way too thick and run the risk of including opaque contaminants on the wood. Gypsum has decent solubility in water. So just add a spoonful of PoP or gypsum at a time and shake vigorously until no more will dissolve and paste starts to rapidly precipitate out. Let it stand, then filter the "clear" liquid This clear liquid is a saturated solution of gypsum. Pad it on the wood and let it dry. As it dries, the gypsum will precipitate out as fine crystals and looks like a white, crusty haze on the wood. You can pad on additional layers until you get a consistent covering, especially on end grain. The refractive index (RI) of the crystal is around 1.53, about the same as most spirit and oil varnishes. Since a crystal is also transparent, once you cover the haze with a varnish with a similar RI, the full transparency of the crystals is restored.
  7. Adding tint to spirit varnish is a very tricky adventure. Unless the pigments are thoroughly dispersed, or in the case of a dye, fully miscible with the varnish, the tint gets pushed around or absorbed unevenly into unsealed wood. Additional layers will melt the previous layer and make the problem worse. A foolproof method is to apply clear, dewaxed shellac in a thin, diluted coat to the bare wood to seal it. Then apply naturally colored shellac. You can find deep amber shellacs from commercial suppliers, or order shellac flakes in a variety of colors and make your own varnish. Apply the colored shellac in successive thin coats until you have the depth of color you like.
  8. A brilliant yellow ground under a darker spirit amber or oil brown varnish can create a strong glowing effect. If one is looking for something more subtle, then a ground with a less intense yellow would do just fine.
  9. The yellow in saffron is due to water soluble carotenoids. It yields a brilliant yellow, highly transparent water-based dye. Sadly, long term light fastness on wood is poor. The experiments I tried included saffron dye over raw spruce and maple and also a PoP ground. The samples were finished with amber shellac and oil-based varnish that had some ultra-violet protection. Within 6 months the underlying color had faded from a golden yellow hue to a light brown. Light exposure was just whatever sunlight filtered through the windows. There has been some success in significantly increasing light fastness by using iron sulfate based/acidic mordants for cotton and wool fabrics. This would suggest a pre-treatment of the wood with a mordant solution before applying the dye might meet with more success. I do not know if this would be a suitable mordant for dyeing wood. I did this more as a curiosity. My current feeling is that modern synthetic water-based dyes specifically formulated for wood staining yield all the light fastness, clarity and brilliance one could possibly want.
  10. I first learned solfege (and chironomy) in 1959 at St. Alphonsus School from Sister Mary Hugh. She passed out books of Gregorian Chants and we mimicked her voice and hand gestures. Sixty years later I can still stumble through relative solfege by sight reading modern music notation, but chant notation and hand conducting are long forgotten. I guess I am saying find a teacher you can mimic and just do it. This seems to be a skill that is mostly acquired through practice rather than theory.
  11. True, but the end pin hole lets one see less than half the fit of the post. Also, if you want to make a large adjustment to a post location for a violin that is already strung up, do you take down the strings, bridge and tail piece before relocating the post?
  12. Frequently, people tend to do what they are taught, and then invent reasons to support the correctness of their approach. Combine this with the common misconception that there can only be one correct way to do a thing, and truly reasoned discussion finds itself homeless. Setting sound post before bridge works, but it is not the only method that works. Setting the bridge first and then holding it in place with light pressure from just the G and E strings, and then setting the sound post also works. Just as well. The idea that the bridge feet are more accurately fitted after the sound post is in assumes significant deformation of the top from the mere insertion of the sound post. Are people really jamming the post in so tight that it has that big an affect on the top's contour? Moreover, do they think the contour would not also change after the substantial load of fully tuned strings press the bridge into the top, further increasing the tightness of the sound post? After bridge and post are in, I monitor the bridge feet fit as I load the strings to see if any final adjustment is called for. Something that would account for plate deformation for both bridge first and post first installations.
  13. If you know someone who is a decent player, I suggest you ask them to go with you to some local shops and try out violins in your price range. You can then hear what other people will hear when you get some skills, and the experienced player can give you feedback on how playable the violin is. Alternately, if you know a player who bought something online and meets the main checkpoints I have listed below, you should be ok. For starting out, you should look for three things: 1. A violin that actually sounds somewhat like a violin. Many inexpensive violins have a weak, high pitched buzzing-like tone. 2. Pegs that turn smoothly and are not a huge hassle to turn and tune the violin. Pegs that bind or easily slip are very common with lower priced violins. Very frustrating. 3. Bridge with a proper contour to give adequate separation among the strings. This is a big problem with cheap violins. The string separation tends to be "flat", making bowing of one string at a time difficult. Finally, remember your budget has to include the purchase of a bow. Carbon fiber bows from about $80US and up should be OK for starting. Cheap, wooden bows tend to be warped or have such soft hairs that bowing becomes a huge challenge.
  14. If you are using a shellac with an intense color added, such as a dye or pigment, then a clear ground/sealer is a good idea for the reasons you mentioned; over absorption of color by the more porous areas of the wood. An additional challenge for such shellacs is consistency of color with added layers, especially for shellacs with pigments. Since successive coats partially melt the previous layer, the pigments in the underlying layers may become streaky.
  15. Thank you for the performance. You resurrected an ancient artifact and used it to provide a transcendent experience to us. Something others have, no doubt, been doing with that violin for centuries. In a sense, that fiddle, through your hands, has provided us with a personal connection to musicians from the past.. Sorry to wax so spiritual. As I age, my natural skepticism tends towards outright cynicism. This was a welcomed check to my decline. >grin<