Is Inharmonicity Perceivable in the Acoustic Guitar

Plucked and struck string instrument sounds are known to exhibit inharmonicity due to stiffness of the strings. Especially in the low piano tones this is very prominent so that the higher partials have frequencies higher than integer multiple of the fundamental frequency. Järveläinen et al (2001) studied the perceivability of inharmonicity for generic string instrument sounds where each harmonic decays with the same rate. While being useful to roughly estimate the threshold where inharmonicity is just noticeable, the importance of this phenomenon in the acoustic guitar has remained unknown. In the present study we have explored this question by listening tests and careful manipulation of the inharmonicity of authentic guitar sounds. A high-resolution parametric modeling technique called FZ-ARMA was applied to estimate the partials of recorded sounds, and these partials were scaled in frequency so that inharmonicity was freely controllable. The results of the listening tests show that the inharmonicity is close to the JND threshold for the four lowest strings while for the two highest strings it is not perceivable. This result was obtained for generally experienced listeners, but it seems that for well trained experts the inharmonicity of low notes is more easily perceived. This implies also that for highest quality sound synthesis of the guitar the inharmonicity must be taken into account, while for an average listener it is questionable if it makes any difference.