Examples of admittance curves measured with the impulse hammer method: Antonio Stradivari’s violin “Ex Benvenuti 1727” and the viola “Dumas” by Giovanni Paolo Maggini (built between 1595 and 1610.).
The first peak at 270.3 Hz (Stradivari) and 229.8 Hz (Maggini) is the Helmholtz resonance, followed by the important top and body resonances. The curves show the strength of the vibrations of the body and thus the timbre and strength of the sound radiation for each individual frequency. They thus represent the “acoustic fingerprint” of the instrument.
With a mouse click on the “Sound” button, the sound is analyzed and graphically displayed (horizontal axis: frequency or tones, vertical axis: harmonics, color: level of the emitted frequency). There are 3 different display modes available: Line spectrum, area spectrum and intensity spectrum. In addition, the “Total Sound Level” (black curve) and the “Harmonic Centroid” (white curve) are displayed for each frequency (note). The Harmonic Centroid indicates where the center of gravity of a sound is located.
line spectrum
Area Spectrum
Intensity Spectrum
You can make the sound audible very easily: either you enter a frequency, or with a click on the note symbol simply the name of the note, or you select “Auto Sweep”, then you hear a glissando over the entire playing range.
You can determine the start and stop frequency, as well as the speed of the sweep. In addition, you can determine the number of harmonics with the “# Harm” arrow keys, and if you want, you can also select the strength of an (artificial) vibrato.
With a mouse click on the speaker symbol of an admittance curve in the “Plots” area you start the sound generator.
If you have loaded several curves (i.e. different instruments), you can simply jump from one instrument to another with a mouse click in the “Plots” area and thus directly compare the sound of different instruments by means of a listening test.
It is important to be aware that this is only about the timbre, because the generator processes the objectively measured characteristics of the instrument. The beginning of the tone, which is individually shaped by the human being with the help of the bow and typical for stringed instruments, and the end of this tone do not exist!
Only a small part of the VIAS software is used for stringed instrument diagnosis. VIAS provides a considerable number of tools from the field of “data processing”, such as measurement error corrections, curve smoothing functions, averaging, simulations and the like. Some of them (curve smoothing and averaging) can be quite useful for admittance measurements on stringed instruments.
