Analysis of handling noises on wound strings

Analysis of handling noises on wound strings
Jyri Pakarinen, Henri Penttinen, and Balazs Bank Laboratory of Acoustics and Audio Signal Processing Helsinki University of Technology Espoo, Finland
This study analyzes the handling noises that take place when a finger is slided along a wound string. The resulting noise has a harmonic structure due to the periodic texture of the wound string. The frequency of the harmonics and the root-mean-square amplitude of the noise were found to be linearly proportional to the sliding speed. In addition, the sliding excites the longitudinal modes of the string, thus resulting in a set of static harmonics in the noise spectrum. The sliding excites different longitudinal modes depending on the sliding location.
Published in J. Acoust. Soc. Am. 122(6), pp. EL197-EL202, Dec. 2007
Sound samples
A spectrogram figure of the handling noise created by sliding a finger on a wound guitar string is presented below. A 12 ms Hamming analysis window was used with 75 % overlap. The noise clearly has a harmonic structure, where the frequency and amplitude of the harmonics increase with the sliding velocity. In addition to the moving harmonics, static harmonics (denoted by arrows) can be found in the spectrum. Click here to hear the sound (played three times).

Spectrograms of the scratch noise on the damped 6th string of an acoustic guitar are presented below. A 23 ms Hamming window with 75 % overlap was used in analysis. The string was scratched with a fingertip, while (a) it had an open length. In (b) and (c), a capo was applied (b) at the third and (c) at the fifth fret. In (a), the dotted white line illustrates the frequency of the 1st and 3rd static harmonics (1400 Hz and 4200 Hz, respectively). In (b) and (c) the white line denotes the frequency where the static harmonics should be located if they were a function of the length of the string. As can be seen, the static resonances coincide well with the dotted lines. Click here to hear examples (a) through (c) played one after another (with short gaps in between). The variation in the longitudinal mode frequencies between samples (a)-(c) can be heard as a timbral change.

The figure below illustrates the averaged power spectrum of the handling noise when the 6th string is scratched at 1/2 (top pane), at 1/3rd (middle pane), and at 1/4th (bottom pane) of the length of the string. A magnitude offset of 20 dB was applied to the spectra, for clarity. An averaging window of 23 ms was used. The k values and the vertical dotted lines denote the longitudinal mode numbers and locations, respectively. Click here to listen to the different scratch noises. In the sound example, the string is first scratched at its midpoint, then after a short break it is scratched at L/3, and finally after a break the scratching is done at L/4.
Author: Jyri Pakarinen
Modified: 3.4.2007, Jyri Pakarinen