Terhardt, E., Zick, M. (1975). Evaluation of the tempered tone scale in normal, stretched, and contracted intonation. Acustica 32, 268-274
Six musical test sounds, each tuned in normal, stretched, and contracted tempered intonation, were subjectively evaluated by 25 musicians and 25 non-musicians in paired-comparison tests. The results indicate that none of the three intonations is optimal for every kind of musical sound. Rather, for tone sequences and for sounds of the type "high melody plus low accompaniment", stretched intonation was first-rate. In chords with medium spectral complexity, normal intonation was optimal, and in case of high spectral complexity even contracted intonation was evaluated as suitable. It is concluded that "ideal" intonation must be flexible, i.e., adapting to the sound's structure at each moment. The relationships of these findings to principles of pitch and roughness perception, musical performance, and intonation of conventional as well as electronic keyboard instruments are discussed.