Study on double decay of individual partials of piano sound—Preliminary results on the ‘‘unison quality.’’

A characteristic of piano tones is their double decay (the initial sound followed by the ‘‘aftersound’’). The difference in mistuning between the three strings of a unison group, and also the adjustment of the regularity of the action of the hammer in the case of important irregularities in hammer striking, are parameters used by the tuner to adjust the temporal evolution of the sound. This study is a part of a more general study to explore what tuners call ‘‘unison quality,’’ which means finding objective and qualitative criteria to decide that the temporal evolution is well adjusted. The results of experiments are reported where the decay of the first 12 partials of real sounds recorded under different conditions is analyzed and then modified by signal processing. The results of informal listening tests indicate that experts (tuner, professional pianists, and composers) are sensitive to these modifications (removal of very brief amplitude falls observed for the different partials). The decay of the different partials seems to be more complex than the double decay observed for the global sound and for the fundamental frequency. Sound illustrations will be presented.